Chapter 9
Birds

Birds belong to the class Aves, which contains dozens of orders. Birds are warm-blooded vertebrates with wings, feathers, and light hollow bones. The vast majority of birds are capable of flight. According to the U.S. Fish and Wildlife Service (FWS), more than 800 species of birds spend all or part of their lives in the United States; more than 9,000 species of birds have been identified around the world.

In addition to taxonomy, birds are broadly classified by their physical characteristics (such as feet or beak structure), eating habits, primary habitats, or migratory habits. For example, raptors or birds of prey have curved beaks and talons well suited for catching prey. This category includes the eagles, vultures, hawks, buzzards, and owls. Perching birds have a unique foot structure with three toes in front and one large flexible toe to the rear. Ducks and geese are known as open-water or swimming birds and have webbed feet. Habitat categories include the sea birds, shore birds, and arboreal (tree-dwelling) birds. Some birds migrate over long distances and others, like turkey and quail, do not migrate at all.

Scientists believe that more than 100 bird species have gone extinct during the course of human history. Bird species have died out because of habitat destruction, hunting and collection, pollution, and predation by nonnative species. The extinction rate of bird species is alarming not only because of the irrevocable loss of each species but also because of implications for the health of entire ecosystems.

ENDANGERED AND THREATENED U.S. SPECIES

As of March 2006 there were ninety bird species listed under the Endangered Species Act (ESA) as endangered or threatened in the United States. (See Table 9.1.) The vast majority have an endangered listing, meaning that they are at risk of extinction. Nearly all have recovery plans in place.

The imperiled birds come from many different genera (plural of genus) and represent a variety of habitats. Most are perching birds, sea birds, or shore birds. There are also a handful of other bird types, including woodpeckers and raptors, such as the bald eagle and northern spotted owl.

Just over $103 million was spent on U.S. bird species under the ESA during fiscal year 2004. Table 9.2 shows the ten species with the highest expenditures. The three most expensive species were the red-cockaded woodpecker ($14.1 million), the southwestern willow flycatcher (nearly $12 million), and the bald eagle in the lower forty-eight states ($9.8 million).

Categories of birds found on the list of endangered and threatened species are described below.

Woodpeckers

Woodpeckers belong to the order Piciformes and the family Picidae. They are characterized by their physiology. They have very hard, chisel-like beaks and a unique foot structure with two toes pointing forward and two toes pointing backward. This allows them to take a firm grip on tree trunks and extend horizontally from vertical surfaces. Woodpeckers prefer arboreal habitats, primarily dead trees in old-growth forests. The birds hammer away at the bark on the trees to dig out insects living there. They often form deep cavities in the tree to use as roosting and nesting holes.

RED-COCKADED WOODPECKERS

The red-cockaded woodpecker (Picoides borealis) is shown in Figure 9.1. The bird is named for the red patches, or cockades, of feathers found on the heads of the males. This species is found in old pine forests in the southeastern United States, where family groups—consisting of a breeding male and female as well as several helpers—nest within self-dug cavities in pine trees. Tree cavities serve as nesting sites in addition to providing protection from

predators. Because red-cockaded woodpeckers rarely nest in trees less than eighty years old, heavy logging has destroyed much of their former habitat. The red-cockaded woodpecker was first placed on the Endangered Species List in 1970. It is currently found in fragmented populations in the southeastern seaboard westward into Texas. Figure 9.2 shows the historical and current distribution of the species in 2002. In 2003 the U.S. Fish and Wildlife Service published an updated recovery plan for the red-cockaded woodpecker and estimated that approximately 14,000 of the birds were in existence at that time.

In March 2001 the Fish and Wildlife Service rescued several red-cockaded woodpeckers from habitat areas in Daniel Boone National Forest in Kentucky. Fifteen woodpeckers in six family groups were relocated to the Carolina Sandhills National Wildlife Refuge in South Carolina and the Ouachita National Forest in Arkansas. Daniel Boone National Forest had become uninhabitable for the woodpeckers after a 1999 infestation of southern pine beetles. The beetles quickly destroyed 90% of local woodpecker habitat despite efforts by Forest Service officials and volunteers to control the insect's spread. The removal of this red-cockaded woodpecker population from Kentucky means that the species is now absent from the state. The bird is also believed extirpated (wiped out) in Maryland, Missouri, New Jersey, and Tennessee.

In September 2005 the FWS initiated a five-year review of the red-cockaded woodpecker to ensure that the endangered status listing is still appropriate for the species.

IVORY-BILLED WOODPECKERS

The ivory-billed woodpecker (Campephilus principalis) is the largest woodpecker species in the United States, with a wingspan up to thirty inches and bodies nearly twenty inches long. The birds have a striking black and white pattern on their bodies and have ivory-colored beaks. The males have brilliant red crests. In the nineteenth century, the species was found throughout the southeastern United States as well as in Cuba. Intense logging and loss of habitat were believed to have driven the birds extinct sometime in the 1940s. Occasional unconfirmed sightings continued to occur over the following decades. John W. Fitzpatrick and his colleagues reported in "Ivory-Billed Woodpecker (Campephilus Principalis) Persists in Continental North America" (Science, June 3, 2005) that scientists at Cornell University had confirmed sightings and a videotape taken of ivory-billed woodpeckers in the Big Woods region of Arkansas. This area is home to the Cache River National Wildlife Refuge. Conservationists are excited that an apparently lost species has been rediscovered.

Passerines

Just over half of all bird species belong to the order Passeriformes and are called passerines. They are informally known as perching birds or songbirds, although not all passerines are truly songbirds. According to the U.S. Department of Agriculture there are more than sixty families in this order, and they include many well-known species, such as robins, bluebirds, larks, blue jays, mockingbirds, finches, wrens, sparrows, swallows, starlings, cardinals, blackbirds, and crows. More than a third of the U.S. species of endangered and threatened birds are passerine (perching) birds.

SOUTHWESTERN WILLOW FLYCATCHER

The southwestern willow flycatcher (Empidonax traillii extimus) is a subspecies of the willow flycatcher. This small bird has a grayish-green back and wings with a pale yellow belly and white-colored throat. It was first listed as endangered in 1995, when less than 600 individuals were believed to be in existence. The bird is found in portions of Arizona, California, Colorado, New Mexico, Nevada, Texas, and Utah. It migrates to Mexico and Central and South America for the winter. The bird feeds on insects and prefers riparian areas (dense vegetation near rivers or streams) for its habitat. It is endangered primarily due to loss of riparian vegetation. In ranching areas, this vegetation is often stripped by grazing livestock. Another factor in the decline is harm from "brood parasites"—bird species that lay their eggs in the nests of other species. Brown-headed cowbirds are brood parasites that threaten the southwestern willow flycatcher. They lay their eggs in the flycatchers nests, and the unsuspecting flycatchers raise the cowbirds' young as their own.

In 1997 the U.S. Fish and Wildlife Service designated critical habitat for the bird in compliance with a court order resulting from a lawsuit filed against the agency by the Southwest Center for Biological Diversity. The critical habitat covered nearly 600 miles of streams and rivers in California, Arizona, and New Mexico. A recovery plan for the bird was finalized in 2002 that includes six recovery units as shown in Figure 9.3. In 2005 the FWS designated new critical habitat for the southwestern willow flycatcher covering 737 miles of waterways in California, Arizona, Nevada, Utah, and New Mexico. The new designation was made in response to a court order.

THE BLACK-CAPPED VIREO AND GOLDEN-CHEEKED WARBLER

The black-capped vireo and golden-cheeked warbler are among the threatened songbirds listed under the Endangered Species Act. Both species nest in central Texas and other locations in the United States and winter in Mexico and Central America. Both species have declined largely due to loss of habitat caused by land clearing for development and invasion of brown-headed cowbirds. In certain areas, more than half the black-capped vireo nests contain eggs of brood parasites called brown-headed cowbirds. The black-capped vireo was placed on the Endangered Species List in 1987; the golden-cheeked warbler was listed in 1990.

Much of the critical nesting habitat for black-capped vireos and golden-cheeked warblers lies in the Hill Country of central Texas. The Texas Hill Country is characterized by diverse habitats and a high concentration of rare bird species. In the last decade, however, increased water demand by metropolitan areas has caused the local Edwards Aquifer to drop by thirty feet, resulting in a 15% to 45% decrease in available bird habitat. In an effort to balance development with wildlife preservation, the city of Austin, Texas, invited the Nature Conservancy to formulate a plan to protect Hill Country habitats while enabling some development. The result was the Balcones Canyonlands Conservation Plan, which includes a 75,000-acre preserve in the Texas Hill Country.

Fort Hood, Texas, a heavy artillery training site for the U.S. Army, was designated essential nesting habitat for the golden-cheeked warbler and black-capped vireo in 1993. With the help of the Nature Conservancy, the Army currently manages some 66,000 acres of habitat for these species. Control of brown-headed cowbird populations has been a major part of the conservation efforts. Brown-headed cowbirds parasitize the nests of over 200 species of songbirds, and have caused declines in many of these species. Nest parasitism rates for the black-capped vireo were as high as 90% before control measures were begun. They have been reduced to less than 10%. Many other bird species also use habitat at Fort Hood, including threatened and endangered species such as the bald eagle, peregrine falcon, and whooping crane.

THE COASTAL CALIFORNIA GNATCATCHER

The coastal California gnatcatcher (Polioptila californica californica) is a small, gray and black songbird known for its kitten-like mewing call. Gnatcatchers are nonmigratory, permanent residents of California coastal sage scrub communities, one of the most threatened vegetation types in the nation. In 1995 the U.S. Geological Survey estimated that more than 85% of coastal sage scrub had been destroyed or significantly degraded in Southern California since the time of European settlement.

The Fish and Wildlife Service estimated in 1993 that approximately 2,500 pairs of California gnatcatchers remained in the United States. The plight of the species has emphasized the importance of preserving coastal sage scrub habitat, which supports many other distinctive species as well. The California gnatcatcher was listed as threatened across its entire range in California and Mexico in 1993. In an effort to protect the birds, in 2003 the FWS proposed a critical habitat area of more than 495,000 acres of land covering portions of Ventura, Los Angeles, Orange, Riverside, San Bernardino and San Diego counties.

Hawaiian Honeycreepers

The Hawaiian honeycreepers are a group of songbirds endemic to Hawaii—that is, species in this group are found there and nowhere else on Earth. Hawaiian honeycreepers are believed to have radiated—formed many separate species, each adapted to a particular life-style—from a single species that colonized the Hawaiian Islands thousands of years ago. The honeycreepers are named for the characteristic "creeping" behavior some species exhibit as they search for nectar. The Hawaiian honeycreepers are extremely diverse in their diet—different species are seed-eaters, insect-eaters, or nectar-eaters. Species also differ in the shapes of the beaks and in plumage coloration. Hawaiian honeycreepers are found in forest habitats at high elevations. According to Abso-luteastronomy.com (http://www.absoluteastronomy.com/reference/hawaiian_honeycreeper) there were some fifty or sixty Hawaiian honeycreeper species originally, but a third of them are already extinct.

Ten species of Hawaiian honeycreepers are currently listed as endangered. Some honeycreeper species are among the most endangered animals on earth, with only a few individuals left. One of the primary factors involved in honeycreeper endangerment is loss of habitat. The Hawaiian Islands are estimated to retain a mere 20% to 30% of their original forest cover. In addition, the introduction of predators that hunt birds or eat their eggs, such as rats, cats, and mongooses, have contributed to the decline of numerous species. The introduction of bird diseases, particularly those spread by introduced mosquitoes, has also decimated honeycreeper populations. The success of mosquitoes in Hawaii has been dependent on another introduced species—pigs. The rooting activity of pigs creates pools of water where mosquitoes lay their eggs. In fact, the greater the number of pigs in a habitat, the more bird disease will be prevalent. Finally, competition with introduced bird species for food and habitat has also been a significant cause of decline.

The Po'ouli is the most endangered Hawaiian honeycreeper and may already be extinct. Along with many other endangered native species, it occupies the Hanawi Natural Reserve Area in Maui, which has been aggressively rehabilitated and cleared of invasive species. The bird was only discovered during the 1970s. At that time less than 200 individuals existed in the wild. By 2004 there were only three Po'ouli birds left. Scientists captured one of the birds, but he died a few months later, apparently of avian malaria. As of March 2006 the remaining two individuals have not been located and may already have died.

In 2003 the U.S. Fish and Wildlife Service published a recovery plan for nineteen endangered Hawaiian forest birds. The agency reports that ten of these species have not been definitely observed in at least a decade and may well be extinct already. Most of these species are native to rain forests at elevations above 4,000 feet on the islands of Hawaii (Big Island), Maui, and Kauai. Major threats to endangered forest species include habitat loss and modification, other human activity, disease, and predation. Of particular importance are nonnative plants, which have converted native plant communities to alien ecosystems unsuitable as habitat.

It is estimated that two-thirds of Hawaii's original bird fauna is already extinct. Of the remaining one-third, a large majority are imperiled. Habitat destruction in Hawaii has been so extensive that all the lowland species now present are nonnative species introduced by humans.

Migratory Songbirds

There are more than 200 species of songbirds known as neotropical migraters. Every year these birds migrate between the United States and tropical areas in Mexico, the Caribbean, and Central and South America. Although some songbirds are appreciated by humans for their beautiful songs and colorful plumage, migratory songbirds also play a vital role in many ecosystems. During spring migration in the Ozarks, for example, dozens of migratory bird species arrive and feed on the insects that inhabit oak trees, thereby helping to control insect populations.

Migratory species are particularly vulnerable because they are dependent on suitable habitat in both their winter and spring ranges. In North America, real estate development has eliminated many forest habitats. Migratory songbird habitats are also jeopardized in Central and South America, where farmers and ranchers have been burning and clearing tropical forests to plant crops and graze livestock. Some countries, including Belize, Costa Rica, Guatemala, and Mexico, have set up preserves for songbirds, but improved forest management is needed to save them.

Raptors (Birds of Prey)

The term raptor is derived from the Latin word raptores, which was once the order on the taxonomy table to which birds of prey were assigned. Eventually scientists split the birds into three orders as follows:

• Accipitriformes—includes hawks, eagles, and buzzards
• Falconiformes—falcons
• Strigiformes—owls

As shown in Table 9.1 there were less than a dozen raptors listed as endangered or threatened in the United States as of March 2006. Species of note include the bald eagle, northern spotted owl, and California condor.

THE BALD EAGLE

The bald eagle (Haliaeetus leucocephalus) is a raptor with special status in the United States. (See Figure 9.4.) A symbol of honor, courage, nobility, and independence (eagles do not fly in flocks), the bald eagle is found only in North America, and its image is engraved on the official seal of the United States of America. There were an estimated 100,000 bald eagles in the country in the late eighteenth century when the nation was founded.

The bald eagle nests over most of the United States and Canada, building its aerie, or nest, in mature conifer forests or on top of rocks or cliffs. Its nest is of such a grand size—sometimes as large as a small car—that a huge rock or tree is necessary to secure it. The birds use the same nest year after year, adding to it each nesting season. It is believed that eagles mate for life. Bald eagles prey primarily on fish, water birds, and turtles.

Bald eagles came dangerously close to extinction in the twentieth century, largely due to the pesticide DDT, which was introduced in 1947. Like other carnivorous species, bald eagles ingested large amounts of DDT by eating prey that had been exposed to it. DDT either prevents birds from laying eggs or causes the eggshells to be so thin they are unable to protect eggs until they hatch. The Bald Eagle Protection Act of 1940, which made it a federal offense to kill bald eagles, helped protect the species. However, numbers continued to dwindle and the bald eagle was listed as endangered in 1967.

Bald eagle populations started to recover with the banning of DDT in 1972. The species also benefited from habitat protection and attempts to clean up water pollution. In 1995 the bald eagle was moved from endangered to threatened status on the Endangered Species List. In 1999 the species was proposed for delisting. A year later all delisting criteria contained in species recovery plans were achieved. However, the FWS has been slow to carry through with the delisting process. In February 2006 the agency reopened the public comment period on the delisting proposal. Public comments were to be accepted until May 2006. The FWS news release announcing the reopening (February 16 2006, http://www.fws.gov/migratorybirds/issues/BaldEagle/Reopening.Comments.06.pdf) notes that there were an estimated 7,066 nesting pairs of bald eagles in the United States at that time.

NORTHERN SPOTTED OWL

The northern spotted owl (Strix occidentalis caurina) occupies old-growth forests in the Pacific Northwest, where it nests in the cavities of trees 200 years old or older. It does not seem afraid of humans and in fact appears to be curious about humans and human activity. Its primary prey includes the nocturnal northern flying squirrel, mice, and other rodents and reptiles. According to the Sierra Club, owl pairs may forage across areas as large as 2,200 acres.

Northern spotted owl populations have declined primarily due to habitat loss. Most of the private lands in its range have been heavily logged, leaving only public lands, such as national forests and national parks, for habitat. Because logging has also been permitted in many old-growth national forest areas, the species has lost approximately 90% of its original habitat. In 1990 the U.S. Fish and Wildlife Service placed the northern spotted owl on its list of threatened species. Court battles began over continued logging in national forest habitats. In 1991 a U.S. federal district court ruled in favor of the Seattle Audubon Society and against the U.S. Forest Service, declaring that the Forest Service was not meeting its obligation to "maintain viable populations." The Forest Service had argued that the FWS was responsible for the management and recovery of this species. However, the court pointed out that the Forest Service had its own distinct obligations to protect species under the Endangered Species Act, and that courts had already reprimanded the FWS for failing to designate critical habitat for the northern spotted owl.

In 1992 the FWS set aside seven million acres as critical habitat for the species and published a recovery plan. A year later the Northwest Forest Plan was established. It reduced logging in thirteen national forests by about 85% to protect northern spotted owl habitats. However, populations of the northern spotted owl continued to decline—this despite the unanticipated discovery of fifty pairs of nesting adults in California's Marin County, just north of the Golden Gate Bridge.

In 2004 the U.S. Fish and Wildlife Service completed a five-year status review of the northern spotted owl. The review was conducted in response to a lawsuit filed by the Western Council of Industrial Workers. The agency concluded that the bird should continue to have a threatened listing under the Endangered Species Act. The FWS found that habitat loss on federal lands has been minimized since the species was originally listed. This success is attributed to the Northwest Forest Plan. However, the agency found that the population of northern spotted owls in Washington, Oregon, and California has continued to decline, and the species faces emerging threats from forest fires, West Nile virus, sudden oak death (a plant disease that has killed hundreds of thousands of trees in California and Oregon), and competition for habitat from barred owls.

In January 2006 the FWS announced its intention to develop a final recovery plan for the northern spotted owl. A draft recovery plan, issued in 1992, was never finalized by the agency. The new recovery plan is expected to address recovery and conservation on non-federal lands and establish delisting criteria. New final designation of critical habit for the species is expected by the end of 2007.

THE CALIFORNIA CONDOR

The California condor (Gymnogyps californianus) has a wingspan in excess of nine feet, and is among the continent's most impressive birds. Ten thousand years ago, this species soared over most of North America. However, its range contracted at the end of the Ice Age, and eventually individuals were found only along the Pacific Coast. Like other vulture species, the California condor is a carrion eater, and feeds on the carcasses of deer, sheep, and smaller species such as rodents. Random shooting, egg collection, poisoning, and loss of habitat devastated the condor population. The spe-cies was listed as endangered in 1967. Oliver H. Pattee and Robert Mesta in "California Condors" (http://biology. usgs.gov/s+t/noframe/b162.htm#9944) show that by 1984 only eleven condors remained in the wild. After five of these birds died, the FWS decided to capture the remaining population.

An intense captive breeding program for the California condor was initiated in 1987. (See Figure 9.5.) The first chick hatched in 1988. The breeding program was successful enough that California condors were released into the wild beginning in 1992. Four years later a release took place near the Grand Canyon, providing spectacular opportunities to view the largest bird in North America. The introduced birds in parts of Arizona, Nevada, and Utah were designated a nonessential experimental population. The California condor is listed as endangered in the remainder of Arizona and all of California and Oregon.

In April 2002, for the first time in eighteen years, a condor egg laid in the wild hatched in the wild. The parents of this chick had been captive-bred at the Los Angeles Zoo and the San Diego Wild Animal Park respectively and released into the wild in 1995 at the age of one. Between 2001 and 2005 three wild-born condor chicks died, one from West Nile virus and two from eating trash (fragments of plastic, metal, glass, and fabric). During the summer of 2005 biologists removed a sickly chick from its nest and performed surgery to remove trash from the bird's stomach. The surgery was successful and the chick was expected to be released back to the wild in the spring of 2006.

In September 2005 the U.S. Fish and Wildlife Service announced that 125 condors were known to be living in the wild and 151 were in captivity at the Los Angeles Zoo, San Diego Wild Animal Park, the Oregon Zoo, and the Peregrine Fund's World Center for Birds of Prey in Boise, Idaho.

Water Birds

Water birds live in and around bodies of water. Some prefer marine (ocean) habitats and others are found only near freshwater. Many species inhabit swamps and wetlands. These areas may be inland or intertidal (along the sea coast).

There were more than two dozen water birds listed as endangered or threatened in the United States as of March 2006. They include a variety of species from many different taxonomic orders.

MIGRATORY SHORE BIRDS

Migratory shore birds are found most often in marshes, mudflats, estuaries, and other wetland areas where the sea meets freshwater. This category includes plovers, stilts, snipes, oystercatchers, avocets, shearwaters, and sandpipers. These birds vary greatly in size and color, but nearly all migrate over very long distances. Most of them breed near the North Pole in the spring and spend their winters anywhere from the southern United States to South America. During their annual migrations, the birds stop to rest and feed at specific locations, known as staging areas, in the United States. Major staging areas include Delaware Bay, the Copper River Delta in Alaska, Cheyenne Bottoms in Kansas, San Francisco Bay, and the Great Salt Lake in Utah.

SEA BIRDS

Sea birds spend most of their time out at sea, but nest on land. They are also known as pelagic birds, because pelagic means oceanic (associated with the open seas). Sea bird species include gulls, terns, albatrosses, puffins and penguins, kittiwakes, petrels, murres and murrelets, auks and auklets, and cormorants.

The marbled murrelet (Brachyramphus marmoratus) is one of a handful of sea birds listed under the Endangered Species Act. The bird was first listed in 1992 and is designated as threatened in California, Oregon, and Washington. The marbled murrelet is about nine inches long and has a distinctive two-tone pattern of dark and light markings. The species prefers to nest in the trees of old-growth forests along the Pacific Northwest coastline. Logging and other causes of habitat degradation have resulted in population declines.

In 2004 the U.S. Fish and Wildlife Service completed a five-year status review for the marbled murrelet. The agency concluded that the population living in Oregon, Washington, and California did not quality for a listing as a distinct population segment under the Endangered Species Act and that the species should retain its listing as threatened. However, the agency has decided to conduct a species-wide review to determine if the listed range of the bird needs to be modified. The status review was performed in response to a lawsuit filed by the American Forest Resources Council and other parties.

WADING BIRDS

Wading birds are unusual birds characterized by long, skinny legs and extended necks and beaks. They wade in the shallow waters of swamps, wetlands, and bays where they feed on aquatic life forms. Wading birds include species of egret, crane, stork, and ibis. As of March 2006 there were two wading birds of note listed under the ESA: the wood stork (Mycteria americana) and the whooping crane (Grus americana).

The wood stork (see Figure 9.6) weighs only about five pounds, but stands up to three feet tall with a five-foot wing span. At one time tens of thousands of the birds inhabited the southeast coastline. In 1984 the species was listed under the ESA as endangered in Alabama, Florida, Georgia, and South Carolina. A recovery plan for the bird was published in 1999. At that time about 5,000 breeding pairs lived in the wild. Populations have declined in the Everglades in southern Florida, but increased in coastal areas farther north. In a 2005 report the FWS estimated the number of adult wood storks to be 16,000 (http://www.fws.gov/northflorida/Species-Accounts/Wood-stork-2005.htm).

Standing five feet tall, the whooping crane (see Figure 9.7) is North America's tallest bird and among the best known endangered species in the United States. Its name comes from its loud and distinctive call, which can be heard for miles. Historically whooping cranes lived across the Great Plains and southeast coast of the United States. The birds were once heavily hunted, for meat as well as for their beautiful, long white feathers. In addition, the heavy loss of wetland areas in the United States deprived whooping cranes of much of their original habitat. In 1937 it was discovered that fewer than twenty whooping cranes were left in the wild in two small populations—a migratory population that nested in Canada and wintered on the Texas coast and a nonmigratory population living in Louisiana.

Each year, the migratory whooping cranes fly 2,500 miles from nesting grounds in Wood Buffalo, Canada, to Aransas, Texas, for the winter before returning north in March to breed. Whooping cranes return to the same nesting site each year with the same mate. In 1937 the Aransas Wildlife Refuge was established in south Texas to protect the species' wintering habitat. Conservation efforts for the whooping crane are coordinated with the Canadian government, which manages the birds' breeding areas.

The whooping crane is listed under the ESA as endangered in Colorado, Kansas, Montana, North Dakota, Nebraska, Okalahoma, South Dakota, and Texas. Nonessential experimental populations were designated in 1993 and 2001 in dozens of states from Wyoming to Florida. In 2001 the first introduced cranes in Wisconsin were led to their Florida wintering grounds along the migration route by ultralight aircraft. The birds successfully made the return trip on their own in following years.

In September 2005 the U.S. Geological Survey reported 340 whooping cranes living in the wild and 135 individuals in captive populations.

OTHER BIRDS

Other birds listed under the Endangered Species Act include nonmigratory shore birds, such as the clapper rail and the Guam rail (a flightless bird); swimming birds, including coots, ducks, eiders, and geese; ground-dwelling birds, such as the prairie chicken; and coastal dwellers, such as the brown pelican.

GENERAL THREATS TO U.S. BIRD SPECIES

The U.S. government has long recognized the importance of bird biodiversity and promoted habitat conservation under the Migratory Bird Conservation Act, passed by Congress in 1929. This law established the Migratory Bird Conservation Commission, which works with the Secretary of the Interior to designate and fund avian wildlife refuge areas. The U.S. Fish and Wildlife Service is responsible for acquiring necessary lands through direct purchase, lease, or easement (agreement with landowners). The agency has procured over four million acres of land for bird refuges. Other domestic laws and international conventions from 1990–2001 concerning migratory birds are listed in Table 9.3.

Habitat Loss and Environmental Decline

The driving force behind current declines in many bird species is the destruction, degradation, and fragmentation of habitat due to increasing human population size and the wasteful consumption of resources. The leading cause of habitat destruction in the United States is agricultural development. Large corporate farms cause environmental damage by clearing out native plant species, planting only one or a few crops, and draining wetlands. Natural habitats are also lost to urban sprawl, logging, mining, and road building.

Pesticides

During the latter half of the twentieth century, pesticides and other toxic chemicals were recognized as a major cause of avian mortality and a primary factor in the endangerment of several species, including the bald eagle and peregrine falcon. While the U.S. Environmental Protection Agency regulates the manufacture and use of toxic chemicals nationwide, the Fish and Wildlife Service (under the Federal Insecticide, Fungicide, and Rodenticide Act) is responsible for preventing and punishing the misuse of chemicals that affect wildlife.

Many chemicals harmful to birds, such as DDT and toxaphene, have been banned. Other chemicals, such as endrin, the most toxic of the chlorinated hydrocarbon pesticides, are still legal for some uses. Endrin was responsible for the disappearance of the brown pelican from Louisiana, a population that once numbered 50,000 individuals.

Oil Spills

Oil spills constitute a major threat to birds. (See Figure 9.8.) One of the worst and most infamous spills in history occurred on March 24, 1989, when the Exxon Valdez tanker released eleven million tons of crude oil into Alaska's Prince William Sound. To many Americans, it still exemplifies the disastrous effects oil spills have on wildlife. Thousands of birds died immediately after coming in contact with the oil, either from losing the insulation of their feathers or by ingesting lethal amounts of oil when they tried to clean themselves. Exxon personnel burned untold piles of birds; others were saved in cold storage under orders from the U.S. Fish and Wildlife Service. A complete count was never obtained, but FWS biologists estimated that between 250,000 and 400,000 sea birds died as a result of the accident.

Approximately 40% of the region's entire population of common murres—estimated at 91,000—was eliminated. The yellow-billed loon population was also seriously depleted, as was the population of Kittlitz's murrelet, a species found almost exclusively in Prince William Sound. Other affected bird species included the bald eagle, black oystercatcher, common loon, harlequin duck, marbled mur-relet, pigeon guillemot, and the pelagic, red-faced, and double-crested cormorants. Of these, according to the Alaska Center for the Environment ("Lingering Effects of the Exxon Valdez Oil Spill," http://www.akcenter.org/oceans/exxon_spill.html), the common loon, the harlequin duck, the pigeon guillemot, and the three species of cormorants had not increased in population size since the spill and were still considered "not recovered" in 2005. In addition, the Kittlitz's murrelet appears to be suffering from continued population decline, and its future prospects appear bleak.

The detergents used to clean up oil spills can also be deadly to waterfowl—detergents destroy feathers, which leads to fatal chills or trauma. Research has shown that even after careful rehabilitation, birds that have been returned to nature after a spill often die in a matter of months. In 1996 Dr. Daniel Anderson, a biologist at the University of California at Davis, found that only 12% to 15% of rehabilitated pelicans survived for two years, compared to the 80% to 90% of pelicans not exposed to oil (Verne G. Kopytoff, "Birds Rescued in Spills Do Poorly, Study Finds," New York Times, November 12, 1996). For many ornithologists, these dismal results raise the issue of whether avian rescue efforts are worthwhile. Could money spent on rehabilitation be better used for spill prevention and habitat restoration? Oregon ornithologist Dr. Brian Sharp argued in the same New York Times article that the cleanup effort might ease the conscience of the public and of politicians, but in reality, does very little to benefit birds. However, new methods of treating oiled birds and of controlling spills have increased the bird survival rate from 5% to between 60% and 80% for some species. Under the Clean Water Act, the oil industry pays a tax that helps fund cleanups after spills.

Domestic Cats

Studies in the United States and Britain have shown that house cats kill millions of small birds and mammals every year, a death toll that contributes to declines of rare species in some areas. Many cat victims are plentiful urban species, but studies by the U.S. Fish and Wildlife Service have shown that cats also kill hundreds of millions of migratory songbirds annually (http://www.fws.gov/birds/mortality-fact-sheet.pdf). In addition, cats have devastated bird fauna on some islands and are believed to have contributed to the declines of several grassland species in the United States.

Trade in Exotic Birds

Birds are among the most popular pets in American homes. According to the American Pet Products Manufacturers Association in 2005/2006 National Pet Owners Survey (http://www.appma.org/press_industrytrends.asp), more than 16.6 million birds are kept as pets in the United States. Many of these are common finches, canaries, or parakeets, all of which are raised in captivity in the United States. However, wild birds are owned and traded as well, including numerous species of passerines (song birds) and psittacines (parrots and their relatives).

The most commonly traded passerines include warblers, buntings, weavers, finches, starlings, flycatchers, and sparrows. Passerines are regarded as low-value birds, and few passerines are endangered due to trade.

The 333 species of psittacines, however, are generally rarer, and thus much more valuable, than passerines. The most commonly traded psittacines are macaws, Amazons, cockatoos, lovebirds, lories, and parakeets. In addition to their vivid colors and pleasant songs, many of these birds possess the ability to "talk," which makes them particularly appealing to some owners. Bird dealers have created demand for an ever-increasing variety of birds, including parrots, macaws, cockatoos, parakeets, mynahs, toucans, tanagers, and other tropical species.

Invasive Species—The Case of Guam

Invasive species have damaged bird populations in some parts of the world, particularly those that occupy islands. Guam's unique bird fauna has been all but wiped out by the brown tree snake, an invasive species. According to Earl William Campbell III in "Brown Treesnake Fact Sheet" (U.S. Fish and Wildlife Service, May 3, 2004), the brown tree snake was probably introduced from New Guinea via ship cargo in the late 1940s. The snake population thrived on the island because of the absence of natural enemies and the presence of plentiful prey in the form of forest birds. There are now believed to be as many as fourteen thousand snakes in a single square mile in some forest habitats. Nine bird species have already gone extinct on Guam, including the Guam flycatcher, the Rufus fantail, the white-throated ground dove, and the cardinal honey-eater. Several other Guam bird species are close to extinction. Many of these birds are or were unique to Guam. Measures have been implemented to try to keep this destructive snake from invading other islands, including careful inspection of all cargo arriving from Guam. The removal of the brown tree snake in select habitat areas on Guam (which is a high effort project, requiring the constant trapping of snakes) allowed the reintroduction of one bird, the flightless Guam rail, in 1998. The Guam rail had gone extinct in the wild, but a population is maintained in captivity.

Other particularly destructive invasive species include several associated with humans, including cats, dogs, and rats, which often prey on birds and their eggs.

BACK FROM THE BRINK—SUCCESS STORIES

The Peregrine Falcon

Many falcon species have declined with the spread of humans. Like other predatory species, falcons were often hunted, either for sport or because they were considered a threat to chickens or livestock.

The peregrine falcon is the fastest bird on Earth. It can achieve diving speeds of over 200 miles per hour. Like the bald eagle, much of the species' decline was due to the pesticide DDT. Populations sank to approximately 325 nesting pairs during the 1930s and 1940s. The recovery of this species was made possible by the banning of DDT as well as the establishment of special captive breeding centers on several continents. Between 1974 and 1999 more than 6,000 peregrine falcons were released into the wild. Federal and state agencies contributed to the conservation effort, as did private organizations such as the Peregrine Fund, Santa Cruz Predatory Bird Research Group, and Midwestern Peregrine Falcon Restoration Project.

In 1996 the U.S. Fish and Wildlife Service declared the peregrine falcon officially recovered and began the process to remove the species from the Endangered Species List. The American peregrine falcon was delisted in 1999 across its entire range. In 2003 the FWS conducted a postdelisting survey to monitor the ongoing condition of the species. At that time 3,000 breeding pairs were counted in the United States, Canada, and Mexico. Another survey will be completed in 2006.

Aleutian Canada Goose

The Aleutian Canada goose was first placed on the Endangered Species List in 1966, when there were an estimated 800 individuals. The species had been thought extinct for several decades until a remnant population was discovered in 1962 by FWS biologists on a remote Aleutian island. Deterioration of habitat and the introduction of predators such as Arctic foxes and red foxes were blamed for the animal's decline. According to the Alaska Department of Fish and Game, in April 2006 the goose population had rebounded to 15,000. Conservation efforts included captive breeding, removal of foxes, and relocation and reintroduction of geese to unoccupied islands. The Aleutian Canada goose was officially delisted in 2001.

FOREIGN SPECIES OF ENDANGERED AND THREATENED BIRDS

As of March 2006 there were 181 foreign species of birds listed under the Endangered Species Act as shown in Table 9.4. Categories including several endangered species are the cranes, eagles, owls, parakeets, parrots, pheasants, pigeons, and warblers.

In the World Conservation Union's 2004 Red List of Threatened Species (2004, http://www.redlist.org) a total of 1,213 bird species were considered threatened out of 9,917 species known and evaluated. Certain groups of birds have declined particularly. All albatross species are considered threatened due largely to deaths from long-line fishing. Many Arctic bird species are threatened by habitat loss due to global warming. Tropical bird species are threatened by large-scale deforestation worldwide. Rapid deforestation in Southeast Asian rainforests has increased the number of threatened doves, parrots, and perching birds. The illegal bird trade has severely harmed many threatened species, particularly in Central and South America.

The largest numbers of endangered birds are found in Indonesia, the Philippines, Brazil, Colombia, China, Peru, India, and Tanzania. Island species are particularly vulnerable to habitat destruction because their ranges are usually very small. In addition, because many island birds evolved in the absence of predators, there are a large number of flightless species—these are highly vulnerable to hunting or predation by introduced species, including humans, cats, dogs, and rats. In fact, the IUCN reports that invasive species represent the single most frequent cause of bird extinctions since 1800.

BIRDS

BIRDS are primarily the epiphanies of the gods and spirits, but they also appear as messengers of the heavenly divine beings. They announce new situations in advance and serve as guides. Moreover, birds symbolize man's soul or spirit as it is released from the body in ecstasy or in death; the bird is a symbol of absolute freedom and transcendence of the soul from the body, of the spiritual from the earthly. Hence, a bird is often associated with divinity, immortality, power, victory, and royalty.

Birds and bird-masked figures are clearly attested as early as the Paleolithic period. In the cave painting at Lascaux in the Dordogne, dating from approximately 15,000 bce, a bird-masked person is depicted as falling backward before a bison confronting him. At his feet lies his spear-thrower, and the spear that he has discharged has pierced the bison's body. Quite close to them is a bird perched on a pole. Most scholars interpret this scene as depicting a hunting tragedy: wearing a bird mask, the hunter has been killed by the bison. The mask may have been used as a device to enable the hunter to approach his prey without being noticed. The bird on a pole may represent the soul of the dead man or the totem and mythical ancestor of the tribe to which he belongs. For other scholars, the scene presents the shamanic trance. The man wearing a bird mask is a shaman; he lies unconscious while his soul has departed for the ecstatic journey to the world beyond. A companion on this spiritual journey is his helping spirit, here symbolized by the bird on a pole. The bison is possibly a sacrificial animal.

Although it is still uncertain whether shamanism originated in the Paleolithic period, birds undoubtedly occupy a very important place in the spiritual world of hunters generally and of northern Eurasia in particular, where shamanism has been a dominant magico-religious force. In fact, the shaman of Inner Asia and Siberia receives help from the spirits of wild animals and birds when undertaking an ecstatic journey. Bird spirits (especially those of geese, eagles, owls, and crows) descend from heaven and enter the shaman's body to inspire him as he beats his drum, wearing the shamanic costume of the bird type. Otherwise, they move into his drum or sit on his shamanic costume. This is precisely when shamanic ecstasy occurs; the shaman is transformed into a spiritual being, a bird in his inner experience. He moves, sings, and flies like a bird; his soul leaves the body and rises toward the heavens, accompanied by bird spirits. This motif of the ascending bird spirit has been revalorized by Daoism on a new spiritual plane: in the Zhuangzi, dating from the third century bce, for example, a huge bird named Peng appears as the symbol of the soaring spirit that enjoys absolute freedom and is emancipated from mundane values and concerns. When a shaman dies among the Yakuts, the Tunguz, and the Dolgans, it is customary to erect on his tomb poles or sticks with a wooden bird at each tip. The bird symbolizes the soul of the departed shaman.

Birds appear in the myths of creation that center on the theme of the cosmogonic dive or the earth diver. In the beginning, when only the waters exist, aquatic birds (ducks, swans, geese, or swallows) dive to the bottom of the primeval ocean to fetch a particle of soil. Birds dive sometimes by God's order and sometimes by their own initiative, but in some variants God transforms himself into a bird and dives. This motif of the diving bird, common among such Altaic peoples as the Buriats and the Yakuts, is also found among the Russians and such Uralic peoples as the Samoyeds, the Mansi, the Yenisei, and the Mari. Earth divers also appear in a certain number of Indian cosmogonic myths of North America. The result of the courageous dive is always the same: a small particle of soil that has been brought up grows miraculously until it becomes the world as it is today. In Finnish and Estonian cosmogonic myths, God flies down as a bird onto the primeval ocean and lays on it the cosmic eggs from which the world emerges. This motif is also found in Indonesia and Polynesia.

Myths of kingship in northern Eurasia are often imbued with the symbolism of birds. According to the Mongolians, a golden-winged eagle gave them the yasa, or basic rules of life on the steppes, and helped them to establish the foundation of the Mongol empire by installing Chinggis Khan on the royal throne. Japanese myths tell how a crow (or raven) and a golden kite flew down as messengers of the heavenly gods and served Jimmu, the first mythical emperor of Japan, as guides in his march through the mountains to Yamato, where he established his imperial dynasty. The Hungarians have the tradition that the Magyars were guided by a giant turul (falcon, eagle, or hawk) into the land where Árpád founded the Hungarian nation. The turul is known as the mythical ancestor of the Árpáds.

These myths of creation and kingship reveal the prominent role played by birds in the formation of the cosmic order. As an epiphany of a god, demiurge, or mythical ancestor, a bird appears in the beginning of the world, and its appearance serves as an announcement of the creation of the universe, of the alteration of the cosmic structure, or of the founding of a people, a dynasty, or a nation. The eagle in Siberia, as well as the raven and thunderbird in North America, is especially invested with the features of the culture hero. Often described as the creator of the world, the bird is the divine being who familiarizes the people with knowledge and techniques, endows them with important cultural inventions, and presents them with the rules of life and social institutions.

In the ancient Near East and the Greco-Mediterranean world, birds are charged with a complex of symbolic meanings. Here, as elsewhere, the bird is essentially an epiphany of deity. In the Near East the dove usually symbolizes the goddess of fertility by whatever name she is known, and in Greece it is especially an epiphany of Aphrodite, the goddess of love. The eagle is a manifestation of the solar deity, as is clearly illustrated by the winged sun disks of Mesopotamia and later of Persia. The eagle is often represented as engaged in fighting with the snake or dragon. This archaic motif, attested in the Near East, India, and the southern Pacific, shows the tension that exists between the celestial solar principle and that of the maternal chthonic forces, but it also reveals man's inextinguishable aspiration for universal oneness or wholeness, which can be achieved by the cooperation and synthesis of conflicting powers.

The bird, and particularly the dove, often symbolizes love as an attribute of the goddess of fertility. In the cults of Dumuzi and Adonis, the goddess appears as a mother who laments over her son's captivity in the underworld and descends there to rescue him, to raise him from the dead. It is possible that the dove's moaning contributed to making it the special symbol of the goddess of love in the ancient Near East. In Greece the dove is an epiphany of divinity, but divinity in its amorous aspect, as can be seen from the dove's association with Aphrodite. In the Greco-Mediterranean world the dove has never lost this erotic connotation.

The eagle, the king of birds, is inseparably associated with royalty as well as with the solar deity. Indeed, royalty has never severed its symbolic ties with the sun and the eagle. In the Near East certain coins depict Hellenistic kings wearing a tiara with a pair of eagles on it facing the sun between them. In utilizing these symbols, the kings declare that they are divine by nature or deified. The divinity of the Roman emperor is expressed through the symbolism of Sol Invictus ("the invincible sun") and the eagle.

More generally, birds in the ancient Near East also signify the immortal souls of the dead. This celebrated image seems to have survived in Islam, where it is believed that the souls of the dead will remain as birds until the Day of Judgment. In Greece, images of the dove on graves may symbolize the soul of the departed, the divinity coming to help the departed, or the soul now in divine form. In Syria, the eagle depicted on tombs is the psychopomp, who leads the soul of the deceased to heaven. On Egyptian tombs the soul of the dead is represented as an androcephalic bird. However, soul birds (hawks, ducks, or geese) in Egypt have more than one function, usually in connection with the mummy. Certainly they are immortal souls, but they also symbolize divine presence and protection; birds bring all sorts of nourishment to the corpse to revive it. Thus in Egypt as elsewhere, the bird is both the soul of the departed and the divinity, regardless of what bird is depicted. The peacock, which in the Greco-Roman world may have symbolized man's hope for immortality, is of Indian origin. In Buddhism not only the peacock but also the owl and many other birds appear as epiphanies of the Buddhas and bodhisattvas, preaching the message of enlightenment and compassion. The bodhisattva Mayūrā-sana, for example, is usually portrayed riding on a peacock.

In Judaism the dove and the eagle, the two most important birds, seem to have kept much the same symbolic values intact although they have been given specific Jewish colorings. The dove depicted on Jewish tombstones, in the wall paintings of Jewish catacombs, and on the ceilings of synagogues signifies Israel the beloved of God, the individual Israelite, or the salvation and immortality given to the faithful by God. In rabbinic tradition, too, the dove symbolizes not only the soul departing at death, but especially Israel the beloved. Moreover, the dove serves as the psychopomp. The eagle is equally multivalent; it is an epiphany of God of the power of God, but it is symbolic also of man's hope for eternal life and immortality.

The Christian symbolism of the dove and the eagle has also undergone a process of revalorization. The dove signifies the Holy Spirit in the baptism of Jesus, but is also becomes the erotic and impregnating force in the Annunciation. The motif of soul birds is well attested in early Christian literature and iconography. The soul becomes a dove at baptism; it identifies thereby with the Holy Spirit, the dove of Jesus' baptism. As a dove, the soul of the departed becomes immortal, soaring up to heaven at death, especially at martyrdom. The eagle as a Christian symbol is bound up with a complex of ideas and images. For early Christians the eagle was symbolic of John the Evangelist because at the beginning of his gospel it is implied that John has risen to the heights of the genealogy of the Logos. But the eagle also symbolizes Jesus Christ himself, and it is believed that as an eagle Christ has accompanied John on his flight in quest of visions. Moreover, the eagle represents the Logos itself, just as in Judaism it signifies God or his power. Finally, the eagle depicted on Christian sarcophagi is inseparably associated with the hope for eternal life, light, and resurrection; it serves as the escort of the souls of departed Christians into immortal life with God.

In Islamic literature and folklore, the symbolism of birds abounds. Farīd al-Dīn ʿAṭṭar's famous epic Manṭiq al-ṭayr (Conversation of the birds) uses the imagery of birds as human souls that journey through the seven valleys and, at the end of the road, discover their identity with the Simurgh, the divine bird that "has a name but no body," a perfectly spiritual being. The Turkish saying "Can kuşu uçtu" ("His soul bird has flown away"), uttered when someone dies, expresses the same concept. And throughout Persian and Persianate poetry and literature, one finds repeatedly the image of the nightingale (bulbul) in love with the radiant rose (gul), representing the soul longing for divine beauty.

Birds are not yet deprived of symbolic meanings. Dreams of flying birds still haunt us. In his masterpiece Demian, Hermann Hesse has given new life to bird symbolism when he speaks of the "bird struggling out of the egg." Modern man's aspiration for freedom and transcendence has also been admirably expressed by the sculptor Constantin Brancusi through images of birds.

See Also

Cocks; Eagles and Hawks; Owls; Swans.

Bibliography

The supreme importance of ornithomorphic symbolism and shamanism in the religious life of Paleolithic hunters has been stressed by Horst Kirchner in his article "Ein archäologischer Beitrag zur Urgeschichte des Schamanismus," Anthropos 47 (1952): 244–286. On the shaman's ecstasy and his transformation into a bird, there is much useful material in Mircea Eliade's Shamanism: Archaic Techniques of Ecstasy (New York, 1964). The bird type of the shamanic costume is illustrated in two works by Uno Harva (formerly Holmberg): The Mythology of All Races, vol. 4, Finno-Ugric, Siberian (Boston, 1927), and Die religiösen Vorstellungen der altaischen Völker (Helsinki, 1938). On the cosmogonic myths of the earth-diver type in which birds play a prominent role, see Mircea Eliade's "The Devil and God," in his Zalmoxis, the Vanishing God: Comparative Studies in the Religions and Folklore of Dacia and Eastern Europe (Chicago, 1972), pp. 76–130. On birds and kingship in Inner Asia and North Asia, see my article "Birds in the Mythology of Sacred Kingship," East and West, n.s. 28 (1978): 283–289. The symbolism of birds in Judaism has been admirably studied by Erwin R. Goodenough in Pagan Symbols in Judaism (New York, 1958), volume 8 of his Jewish Symbols in the Greco-Roman Period. The best single book by a folklorist on folk beliefs and customs concerning birds is Edward A. Armstrong's The Folklore of Birds: An Enquiry into the Origin and Distribution of Some Magico-Religious Traditions, 2d ed., rev. & enl. (New York, 1970).

New Sources

Estela Núñez, Carmen. "Asai, a Mythic Personage of the Ayoreo." Latin American Indian Literatures 5 (Fall 1981): 64–67.

Luxton, Richard N. "Language of the Birds: Tales, Texts and Poems of the Interspecies Communication." Latin American Indian Literatures Journal 3, no. 1 (Spring 1987): 61–62.

Seligmann, Linda J. "The Chicken in Andean History and Myth: The Quechua Concept of Wallpa." Ethnohistory 34 (Spring 1987): 139–170.

Waida, Manabu. "Problems of Central Asian and Siberian Shamanism." Numen 30 (December 1983): 215–239.

Manabu Waida (1987)

Revised Bibliography

Birds

Characterization

Resources

Birds are vertebrate animals in the class Aves. There are approximately 8, 800 species of birds, divided among 28 living orders. Of these, slightly more than 900 species are found in North America. There has been considerable disagreement among ornithologists about the appropriate level for differentiating species, leading to multiple classification schemes. But however one distinguishes between species, each species belongs to a larger group, called a genus; each genus belongs to a family; and each family belongs to an order. One order, the Passeriformes or perching birds, accounts for more than half of the living species of birds.

Birds are believed to have evolved from saurischian dinosaurs about 150 million years ago. The first truly birdlike animal was Archaeopteryx lithographica, which lived during the Jurassic period, about 130 million years ago. This 3-foot (1 m) long animal is considered to be an evolutionary link between the birds and the dinosaurs. Archaeopteryx had teeth and other dinosaurian characters, but it also had a feathered body and could fly.

Characterization

Birds can often be characterized by their habitats. Species are more likely to be found in a single habitat in the tropics, than in more temperate regions, with variable climates, where they may have to accommodate several environments. During times of migration, birds may show up in very nontraditional places. Major habitats that serve as homes to birds include polar regions; tundra; alpine regions; coniferous forests; deciduous forests; tropical rainforests; grasslands;

deserts; freshwater lakes, ponds, and streams; shore and marshes; and seas.

Most species of birds will defend their territories, particularly in nesting season, against other birds that happen to stray into the area, and are perceived to be a threat to the nest. Territories generally fall into the following categories: mating, nesting and feeding; mating and nesting; mating; narrowly restricted nesting; feeding; wintering; roosting; and group territory.

Some birds prefer to live apart from other birds, while others are more social. Certain mated woodpeckers, for example, seem to constantly resent each other, and go out of their way to avoid each other’s presence. Australian wood swallows, on the other hand, feed, bathe, roost, attack predators, breed, preen, perform aerial acrobatics, and feed each other in a communal fashion. Assembly into a flock (consisting of either a single species or several different species) offers the advantage of more eyes and ears for spotting predators and finding new food sources.

Most birds have distinctive calls. Males may sing to warn off rivals, or to attract a mate. Some species have separate calls for courtship and for communication. Bird calls serve several functions including: reproductive functions (to proclaim the sex of an individual, advertise for a mate, or establish territorial sovereignty); social functions (space out birds in a given environment, teach the young their species’ song, or convey information about food and enemies); or individual functions (provide emotional release, identify individuals to each other, or simply to perfect a song).

All birds have feathers, and in this way are unlike any other type of animals. Most birds lose their old feathers each year, and have them replaced by new ones in a process called molting. Usually, molting occurs when the bird is neither nesting nor migrating. Some birds will undergo a complete molt in the summer or fall, and then a partial molt in the spring (replacing feathers of the body and head). The chief functions of feathers are to protect the body and to promote flight.

Because birds have four limbs, they are referred to as tetrapods. However, the forelimbs are highly modified into structures known as wings, which are used primarily for flying or gliding. The hind limbs are used mostly for walking or hopping, so these animals are bipedal when moving on the ground. Some species of birds are flightless, but most can fly or soar well.

The bones of all flying birds are modified for flight, and are relatively light with many hollow regions. The flying birds have a strongly keeled breastbone, or sternum, to which the flight muscles are attached. The pelvic bones are fused into a structure known as a synsacrum. Birds have a relatively long neck and their mandibles are modified into a keratinous beak. They do not have teeth. Birds have a four-chambered heart and a double circulation of the blood, with complete separation of oxygenated and de-oxygenated blood.

Approximately 90% of all birds are monogamous, which is to say that one male bonds with one female. Bonds may last for one nesting period (e.g., house wrens), an entire breeding season (most species), several seasons (e.g., American robins), or life (e.g., geese, swans, hawks, albatrosses, and loons). Current thinking is that most monogamous birds probably mate outside of the primary pair bond, but the pair contributes substantially only to the raising of young in their own nest. Most birds whose young are reared in a nest form monogamous pairs. But monogamous versus polygamous relationships are not rigidly fixed in some species. Swans, hawks, doves, finches, and thrushes, for example, normally show monogamous behavior but occasionally form polygamous bonds.

Situations in which one male mates with more than one female, while each female mates with only one male, are referred to as polygyny. Scientists have noted that when male birds hold territories that vary greatly in the quality of resources, females tend to choose males with high-quality territories as mates. Given the choice between a poor nesting territory and becoming the second mate of a male with a high quality territory, many females will opt for the latter course. In other cases, where territoriality does not appear to be a factor, an over-abundance of resources may also lead to polygyny. In North America, red-winged blackbirds and yellow-headed blackbirds sometimes form polygynous relationships.

There are also rare mating systems in which one female mates with more than one male, while each male mates with only one female (known as polyandry). Two forms of polyandry are known. In one case, the female holds a large territory that includes the nesting territories of two or more males who care for the eggs and the young, such as the spotted sandpipers and red phalaropes of North America. In an even rarer type of polyandry, more than one male may mate with a single female with the resultant offspring reared collectively by the female and her mates. The North American acorn woodpecker occasionally exhibits this type of cooperative polyandry.

Courtship behavior may include dances, feeding rituals, flights, posturing, and cries. Frequently, courtship displays highlight some distinctive feature of the male bird’s plumage. In addition to singing, male birds may vibrate their wings, fluff their body feathers, raise their bills, thrust their head forwards, or run by taking short steps. But other birds may advertise their skills rather than their coloring to attract a mate. In its courtship behavior, for example, the male tern finds it sufficient to display a freshly caught fish to a potential mate.

Female birds are fertilized internally. They are oviparous, laying relatively large, hard-shelled eggs, with a discrete yolk. The eggs are incubated by one or both parents. The young of almost all species of birds are cared for by their parents.

Birds tend to build nests to cradle their eggs, rather than residences. (Compared to nesting behavior, nighttime roosting behavior is poorly understood.) The construction of nests can range from very basic to highly complex. Some birds will use a nest repeatedly, while others will build a new nest for each new brood. Although each type of bird has a preferred site for its nest, some birds may be very adaptable in their choice of sites. The female usually builds the nest, though the males of some species may assist. Materials used in building may be of animal, vegetable, or mineral origin, but plant materials are most commonly used.

The number of eggs laid varies widely from species to species. This number may depend on the temperature of the environment, the time in the season, or the size of the food supply. Birds incubate eggs by sitting on them and keeping them warm. During the brooding period, some birds may develop a brooding patch on their bellies where feathers and extra blood vessels develop to provide warmth. The number of broods raised in a single year depends on the length of the available season, and the time it takes for one brood to reach independence. There is some evidence that birds living under crowded conditions are less likely to lay extra clutches in a given year.

Upon hatching, young birds may be active and wide-eyed (precocial), or blind and immobile (altricial). Some precocial birds are able to find their own food immediately after being hatched. Most altricial young remain in the nest for several weeks after they learn to leave it. Among precocial species, young birds may be completely independent of their parents, as in the megapodes; or they may follow their parents but find their own food (e.g., ducks and shorebirds). Others may follow their parents, who point out food to them, for example, quail and chickens. Still others, like grebes and rails, may follow their parents and be fed by them.

The young of semiprecocial species are active and wide-eyed at birth. They remain in the nest even though they are able to walk, so they can be fed by their parents (e.g., gulls and terns). Semi-altricial young are unable to leave the nest, and may be born with their eyes open (e.g., herons and hawks), or with their eyes closed (e.g., owls). Passerines are examples of altricial species.

Although few birds are completely vegetarian, most eat plant material. Some birds are seed-eaters, others feed on fruit and berries, and still others feed on buds and green shoots of plants. Waterfowl may eat various parts of aquatic plants and aquatic creatures such as marine worms. But, without insects and other arthropods such as spiders, most birds would starve. Some birds employ a variety of foraging methods to find their food, while others have a much narrower range of techniques. In addition to food, birds must have water, which they either drink or obtain from the foods they eat.

Birds require large and dependable sources of rich food to sustain their high metabolisms. Although some birds are able to sustain themselves by only moving a few miles from where they were hatched, most birds, at least in the temperate zones, move from place to place with the change in seasons. Geese and cranes appear to learn their migration routes by accompanying their elders, but other birds, including many songbirds, seem to reach their wintering grounds by pure instinct. Clues to migratory routes may be provided by the position of the sun, the positions of the stars, the earth’s magnetic field, and the sound of the ocean crashing against the shore.

Man’s fascination with birds dates back thousands of years. Old World cave drawings show ostriches, auks, grouse, passerines, snowy owls, swans, ducks, eagles, and others. Men were even painted with birds’ heads. Ancient myths suggest that early humans viewed birds not only as food sources, but as colorful mystical creatures capable of flight and disappearance, with the gift of song.

Although there is little doubt that most birds are beneficial, or at least not harmful, to human interests, they are frequently perceived as pests. While birds have wreaked economic havoc on some agricultural activities, they also feed on insects, rodents, and other species that destroy crops.

Both intentionally and unintentionally, humans has destroyed many bird species. Two hundred years ago, birds were considered such an inexhaustible resource that the wholesale slaughter of a species, leading to its extinction, hardly raised an eyebrow.

KEY TERMS

Brood— To sit on or hatch eggs.

Molt— To periodically shed all or part of a bird’s feathers.

Monogamy— The practice of having only one mate.

Ornithology— The branch of zoology concerned with the study of birds.

Oviparous— Producing eggs that hatch outside of the body.

Passeriformes— Perching birds, an order whose members have four toes, three directed forward and one backward, and all joining the foot at the same level.

Passerines— Members of the order Passeriformes, which includes perching birds and songbirds such as jays, blackbirds, warblers, and sparrows.

Polyandry— A mating pattern in which a female mates with more than one male in a single breeding season.

Polygyny— A mating pattern in which a male mates with more than one female in a single breeding season.

But the greatest impact man has had on birds occurred through expansion into their natural habitats with the construction of farms, cities, roads, and industrial buildings. A by-product of industrial development has been widespread environmental pollution, including pesticides and other noxious species. Intended to rid fields of such insects as the fire ant, pesticides have accumulated in many places traditionally frequented by birds, where they have been subsequently ingested by them. Oil spills have also taken their toll on bird populations. Not surprisingly, many species have disappeared as a result of encroachment into their natural environment. According to one estimate, 85 species of birds, representing 27 families, have become extinct since 1600.

The best approach to limiting human impact on birds is the simplest: if people would limit destruction of the natural environment, many threatened species’ habitats could be preserved. Other interventions that could protect bird populations include checks on unbridled commercial and residential development, and the dumping of environmental pollutants. But for man to adopt these measures would require a fundamental change in attitude toward the environment, which is paradoxically only likely to occur through gaining greater first-hand knowledge of nature in its unspoiled state.

See also Birds of prey;Chordates; Shore birds; Song birds.

Resources

BOOKS

Ehrlich, Paul R., David S. Dobkin, and Darryl Wheye. The Birder’s Handbook. New York: Simon & Schuster Inc., 1988.

Forshaw, Joseph. Encyclopedia of Birds. New York: Academic Press, 1998.

Mitchell, A. The Guide to Trees of Canada and North America. Surrey, U.K.: Dragon’s World Ltd., 1987.

Peterson, Roger Tory. North American Birds. Houghton Mifflin Interactive (CD-ROM), Somerville, MA: Houghton Miflin, 1995.

Sibley, David Allen. The Sibley Guide to Birds. New York: Knopf, 2000.

OTHER

Public Broadcasting Service (PBS). “The Life of Birds” <http://www.pbs.org/lifeofbirds> (accessed November 2, 2006).

University of California Museum of Paleontology. “Introduction to the Aves” <http://www.ucmp.berkeley.edu/diapsids/birds/birdintro.html> (accessed November 2, 2006).

Birds

Birds are vertebrate animals in the class Aves. There are approximately 8,800 species of birds, divided among 28 living orders. Of these, slightly more than 900 species are found in North America . There has been considerable disagreement among ornithologists about the appropriate level for differentiating species, leading to multiple classification schemes. But however one distinguishes between species, each species belongs to a larger group, called a genus; each genus belongs to a family; and each family belongs to an order. One order, the Passeriformes or perching birds, accounts for more than one-half of the living species of birds.

Birds are believed to have evolved from saurischian dinosaurs, about 150 million years ago. The first truly bird-like animal was Archaeopteryx lithographica, which lived during the Jurassic period, about 130 million years ago. This 3 ft (1 m) long animal is considered to be an evolutionary link between the birds and the dinosaurs. Archaeopteryx had teeth and other dinosaurian characters, but it also had a feathered body and could fly.

Characterization

Birds can often be characterized by their habitats. Species are more likely to be found in a single habitat in the tropics, than in more temperate regions (with variable climates) where they may have to accommodate several environments. During times of migration , birds may show up in very non-traditional places. Major habitats that serve as homes to birds include polar regions; tundra ; alpine regions; coniferous forests ; deciduous forests; tropical rainforests; grasslands ; deserts; freshwater lakes, ponds, and streams; shore and marshes; and seas.

Most species of birds will defend their territories, particularly in nesting season, against other birds that happen to stray into the area, and are perceived to be a threat to the nest. Territories generally fall into the following categories: mating, nesting, and feeding; mating and nesting; mating; narrowly restricted nesting; feeding; wintering; roosting; and group territory.

Some birds prefer to live apart from other birds, while others are more social. Certain mated woodpeckers , for example, seem to constantly resent each other, and go out of their way to avoid each other's presence. The Australian wood swallows, on the other hand, feed, bathe, roost, attack predators, breed, preen, perform aerial acrobatics, and feed each other in a communal fashion. Assembly into a flock (consisting of either a single species or several different species) offers the advantage of more eyes and ears for spotting predators and finding new food sources.

Most birds have distinctive calls. Males may sing to warn off rivals, or to attract a mate. Some species have separate calls for courtship and for communication. Bird calls serve several functions including: reproductive functions (to proclaim the sex of an individual , advertise for a mate, or establish territorial sovereignty); social functions (space out birds in a given environment, teach the young their species' song, or convey information about food and enemies); or individual functions (provide emotional release, identify individuals to each other, or simply to perfect a song).

All birds have feathers, and in this way are unlike all other types of animals. Most birds loose their old feathers each year, these being replaced by new ones (molting). Usually, molting occurs when the bird is neither nesting nor migrating. Some birds will undergo a complete molt in the summer or fall, and then a partial molt in the spring (replacing feathers of the body and head). The chief functions of feathers are to protect the body and to promote flight.

Because birds have four limbs, they are referred to as tetrapods. However, the fore limbs are highly modified into structures known as wings, which are primarily used for flying or gliding. The hind limbs are mostly used for walking or hopping, so these animals are bipedal when moving on the ground. Some species of birds are flightless, but most can fly or soar well.

The bones of all flying birds are modified for flight, and are relatively light with many hollow regions. The flying birds have a strongly keeled breastbone or sternum, to which the flight muscles are attached. Their pelvic bones are fused into a structure known as a synsacrum. Birds have a relatively long neck and their mandibles are modified into a keratinous beak. They do not have teeth. Birds have a four-chambered heart and a double circulation of the blood , with complete separation of oxygenated and de-oxygenated blood.

Approximately 90% of all birds are monogamous, which is to say that one male bonds with one female. Bonds may last for one nesting period (e.g., house wrens ), an entire breeding season (most species), several seasons (e.g., American robins ), or life (e.g., geese , swans , hawks , albatrosses , and loons ). Current thinking is that most monogamous birds probably mate outside of the primary pair bond, but the pair contributes substantially only to the raising of young in their own nest. Most birds whose young are reared in a nest form monogamous pairs. But monogamous versus polygamous relationships are not rigidly fixed in some species. Swans, hawks, doves, finches , and thrushes , for example, normally show monogamous behavior but occasionally form polygamous bonds.

Situations in which one male mates with more than one female, while each female mates with only one male, are referred to as polygyny. Scientists have noted that when male birds hold territories that vary greatly in the quality of resources, females tend to choose males with high-quality territories as mates. Given the choice between a poor nesting territory and becoming the second mate of a male with a high quality territory, many females will opt for the latter course. In other cases, where territoriality does not appear to be a factor, an overabundance of resources may also lead to polygyny. In North America, red-winged blackbirds and yellow-headed blackbirds sometimes form polygynous relationships.

There are also rare mating systems in which one female mates with more than one male, while each male mates with only one female (known as polyandry). Two forms of polyandry are known. In one case, the female holds a large territory that includes the nesting territories of two or more males who care for the eggs and the young, such as the spotted sandpipers and red phalaropes of North America. In an even rarer type of polyandry, more than one male may mate with a single female with the resultant offspring reared collectively by the female and her mates. The North American acorn woodpecker occasionally exhibits this type of cooperative polyandry.

Courtship behavior may include dances, feeding rituals, flights, posturing, and cries. Frequently, courtship displays highlight some distinctive feature of the male bird's plumage. In addition to singing, male birds may vibrate their wings, fluff their body feathers, raise their bills, thrust their head forwards, or run by taking short steps. But other birds may advertise their skills rather than their coloring to attract a mate. In its courtship behavior, for example, the male tern finds it sufficient to display a freshly caught fish to a potential mate.

Female birds are fertilized internally. They are oviparous , laying relatively large, hard-shelled eggs, with a discrete yolk. The eggs are incubated by one or both parents. The young of almost all species of birds are cared for by their parents.

Birds tend to build nests to cradle their eggs, rather than as residences. (Compared with nesting behavior, the night-time roosting behavior of most birds is poorly understood.) The construction of nests can range from very basic to highly complex. Some birds will use a nest repeatedly, while others will build a new nest for each new brood. Although each type of bird typically has a preferred site for building its nest, some birds may be very accommodating in their choice of nesting sites. It is usually the female that builds the nest, though the males of some species may assist. The materials used in the building of a nest may be of animal, vegetable, or mineral origin, but plant materials are most commonly used.

The number of eggs laid by the female varies widely from species to species. This number may depend on the temperature of the environment, the time in the season, or the size of the food supply. For the most part, only birds incubate eggs by sitting on them and keeping them warm. During the brooding period, some birds may develop a brooding patch on their bellies where feathers and extra blood vessels develop to keep the eggs warm. The number of broods raised in a single year depends on the length of the available season, and the time it takes for one brood to reach independence. There is some evidence that birds living under crowded conditions are less likely to lay extra clutches in a given year.

Upon hatching, young birds may be active and wide-eyed (precocial), or blind and immobile (altricial). Some precocial birds are able to find their own food immediately after being hatched. Most altricial young remain in the nest for several weeks after they learn to leave it. Among precocial species, young birds may be completely independent of their parents, as in the megapodes; or they may follow their parents but find their own food (e.g., ducks and shorebirds). Others may follow their parents, who point out food to them, for example, quail and chickens. Still others, like grebes and rails , may follow their parents and be fed by them.

The young of semi-precocial species are active and wide-eyed at birth . They remain in the nest even though they are able to walk, so they can be fed by their parents (e.g., gulls and terns ). Semi-altricial young are unable to leave the nest, and may be born with their eyes open (e.g., herons and hawks), or with their eyes closed (e.g., owls ). The passerines are examples of altricial species.

Although few birds are completely vegetarian, most eat plant material. Some birds are seed-eaters, others feed on fruit and berries, and still others feed on buds and green shoots of plants. Waterfowl may eat various parts of aquatic plants and aquatic creatures such as marine worms. But, without insects and other arthropods such as spiders, most birds would starve. Some birds may employ a variety of foraging methods to find their food, while others may have a much narrower range of techniques. In addition to food, birds must have water , which they either drink or obtain from the foods they eat.

Birds require large and dependable sources of rich food to sustain their high metabolisms. Although some birds are able to sustain themselves by only moving a few miles from where they were hatched, most birds, at least in the temperate zones, move from place to place with the change in seasons. Geese and cranes appear to learn their migration routes by accompanying their elders, but other birds, including many songbirds, seem to reach their wintering grounds by pure instinct . Clues to migratory routes may be provided by the position of the sun , the positions of the stars, the earth's magnetic field , and the sound of the ocean crashing against the shore.

Man's fascination with birds dates back thousands of years. Old World cave drawings show ostriches, auks , grouse , passerines, snowy owls, swans, ducks, eagles , and others. Men were even painted with birds' heads. Ancient myths suggest that early man viewed birds not only as food sources, but as colorful mystical creatures capable of flight and disappearance, and the gift of song.

Although there is little doubt that most birds are beneficial, or at least not harmful, to the interests of man, they are frequently perceived as pests . While it is true, birds have wreaked economic havoc on some of man's agricultural activities, it should not be forgotten that birds also feed on insects, rodents , and other life forms that destroy crops .

Both intentionally and unintentionally, man has destroyed many bird species. Two hundred years ago, birds were considered such an inexhaustible resource that the wholesale slaughter of a species, leading to its extinction , hardly raised an eyebrow. But the greatest impact man has had on birds occurred through his expansion into their natural habitats with the construction of farms, cities, roads, and industrial buildings. A by-product of industrial development has been widespread environmental pollution , including pesticides and other noxious species. Intended to rid fields of such insects as the fire ant, pesticides have accumulated in many places traditionally frequented by birds, where they have been subsequently ingested by them. Oil spills have also taken their toll on bird populations. It is not surprising, therefore, that many species have disappeared as a result of man's encroachment on the natural environment. According to one estimate, 85 species of birds, representing 27 families, have become extinct since 1600.

The best approach to limiting man's impact on birds is the simplest one: if man would limit his destruction of the natural environment, many of the habitats of threatened species could be preserved. Interventions that could protect bird populations include checks on unbridled commercial and residential development, and the dumping of environmental pollutants. But for man to adopt these measures would require a fundamental change in his attitude toward the environment, which is paradoxically only likely to occur through his gaining greater first-hand knowledge of nature in its unspoiled state.

See also Birds of prey; Chordates; Shore birds; Song birds.

Resources

books

Ehrlich, Paul R., David S. Dobkin, and Darryl Wheye. The Birder's Handbook. New York: Simon & Schuster Inc., 1988.

Forshaw, Joseph. Encyclopedia of Birds. New York: Academic Press, 1998.

Mitchell, A. The Guide to Trees of Canada and North America. Surrey, U.K.: Dragon's World Ltd., 1987.

Peterson, Roger Tory. North American Birds. Houghton Mifflin Interactive (CD-ROM). Somerville, MA: Houghton Miflin, 1995.

Sibley, David Allen. The Sibley Guide to Birds. New York: Knopf, 2000.

KEY TERMS

Brood

—To sit or hatch eggs.

Molt

—To periodically shed all or part of a bird's feathers.

Monogamy

—The practice of having only one mate.

Ornithology

—The branch of zoology concerned with the study of birds.

Oviparous

—Producing eggs that hatch outside of the body.

Passeriformes

—An order of birds whose members have four toes, three directed forward and one backward, and all joining the foot at the same level.

Passerines

—Members of the order Passeriformes, which includes perching birds and songbirds such as jays, blackbirds, warblers, and sparrows.

Polyandry

—A mating pattern in which a female mates with more than one male in a single breeding season.

Polygyny

—A mating pattern in which a male mates with more than one female in a single breeding season.

Birds

A bird is a warm-blooded vertebrate (an animal with a backbone) that has feathers, a beak, and two wings. Its most unique feature is the ability to fly, although not every bird is able to fly. All birds hatch from eggs and their bodies have evolved a wide range of adaptations that enable them to fly. Birds are found in nearly all parts of the world.

JOHN JAMES AUDUBON

American ornithologist (a person specializing in the study of birds) John James Audubon (1785–1851) was the most famous artist and naturalist in nineteenth-century America. He not only kept finely detailed studies of birds, but produced the first modern atlas of ornithology. This atlas is also considered to be one of the most beautiful natural history books ever made.

John James Audubon was born in what is now Haiti, the son of a French sea captain who owned a plantation on that island. After spending his first few years there, he moved to Paris, France, and studied painting for a short time. Audubon was eventually sent to America when he was eighteen years old in order to avoid being inducted into the army of Napoleon. Throughout his boyhood, he continuously collected and sketched birds, plants, and insects. He also developed the habit of keeping detailed notes of whatever he observed. At his father's estate at Mill Grove, near Philadelphia, Pennsylvania, he conducted what appear to be the first known bird-banding experiments in North America. In order to learn more about the movements and habits of a bird called the Eastern Phoebe, he caught them, tied bits of colored string on their legs, and was able to prove that they returned to the same nesting sites the following year.

After Audubon married Lucy Blakewell in 1808, he tried to become a storekeeper, but found himself unable to stay indoors long enough to run a store. As a natural-born outdoorsman, he was unable to make himself stay away from studying the things he loved. After his business failed, and he went bankrupt (and even spent some time in jail), he decided to pursue what he really loved and dedicated himself to what he now called his "great idea." He would travel throughout America and draw, in life-size scale, every bird on the continent. Thus, at the age of thirty-five, Audubon set off, with his wife's blessing, to pursue his ornithological dream. Audubon's wife worked as a governess and teacher to help support him, although he would sometimes paint portraits and street signs when they needed money. For five years Audubon traveled the American wilderness painting its bird life. Where most bird painters before him had worked from long-dead, stuffed specimens and drew them in a not very true-to-life way, Audubon pioneered the use of fresh models. He would shoot a bird and wire into a life-like pose in order to try and capture it accurately. It must be remembered that in the early nineteenth century, little thought was ever given to the conservation of birds or any other animals, and it was common for Audubon to shoot several of the same species until he found one that he considered perfect for painting. From the beginning, Audubon's "great idea" ambitiously included the goal of painting every bird in its real, life-size dimensions. He was able to do this for most birds by having a single book page measure more than 3.5 feet (1.07 meters) by 2.5 feet (0.76 meters). This was larger than any book published to that time. For the very large birds like the whooping crane, he would paint them life-size but have their heads bending toward the ground, so that the drawing would fit on a page.

By 1825, Audubon had compiled a spectacular set of bird paintings, but when he could interest no American publisher in his work, he went to England. There his work was recognized, and he began to enlist "subscribers," either individuals or institutions, who agreed to buy the book when published. The actual production of his great work took many years since the plates (a full-page book illustration) were all hand-colored. The first volume of Birds of Americaappeared in 1827, and the fourth and last volume was published in 1838. Altogether, the books contain 435 hand-colored pictures. Later, Audubon published a five-volume work of bird descriptions to accompany the illustrated work. The production of Birds of Americawas extremely expensive, and a subscriber paid approximately $1,000 for the set, an extremely high price in the early nineteenth century.

Despite the fact that Audubon probably killed more birds than most anyone of his time, he had dedicated his life to capturing their beauty and the essence of their liveliness, and he truly must have also loved birds more than anyone of his time. Today, his name is linked to that of a modern conservation organization, the National Audubon Society, and there are many local Audubon societies throughout America dedicated to learning about and conserving birds.

CHARACTERISTICS OF BIRDS

From the soaring eagle to the flightless penguin, from the clumsy loon to the graceful swan, birds come in the widest variety imaginable. All have several characteristic features that distinguish them from other animals Only birds have feathers. While other types of animals may have hair or scales or a shell covering their bodies, feathers are unique to birds. As with just about everything in the way they have evolved, a bird's over-lapping feathers give it the ability to fly. The most important factor in flight, whether it is a bird or an airplane, is weight. The heavier something weighs, the more energy is required to get it off the ground and keep it in the air. Feathers are therefore, by design, a lightweight covering for a bird. Like human hair or a bull's horn, feathers are made of a protein called keratin. Although feathers vary in size, shape, and texture, they share a basic frame or structure: a base like a tube that goes up into a central shaft that itself branches into vanes. A bird actually has several different types of feathers. Short, fluffy, down feathers that are closest to the skin serve as insulation. Powder feathers produce a type of powder that makes a bird waterproof. Contour feathers give the bird a streamlined shape. Flight feathers are strong and provide lift much like an airplane wing. Tail feathers are stiff and provide steering, balance, and control. Altogether, a bird's feathers are the perfect covering for its wings. Birds are able to fly because when air passes over their wings, they receive an upward push or lift. Feathers also act as a good insulator and keep a bird warm by helping it retain its body heat.

All birds have two feet and one beak, although there can be some very dramatic differences. The shape and structure of both beaks and feet give a good indication of what a bird eats and what type of habitat it lives in. The long, tubelike beak of a hummingbird is adapted for sucking nectar from a flower, while a bird of prey like an eagle has a sharp, hooked beak for holding and tearing its meal. Finches have short beaks that are thick and strong for cracking open seeds, and a typical marsh bird has an upward-curved, spoonlike bill for sifting water. Ducks have webbed feet for swimming atop water, while hunters and meat-eaters like hawks have sharp talons that grip and kill their prey. Other birds simply have toes that enable them to perch on branches. Most birds have four toes—three in front and one in back.

Finally, all birds are endothermic or warm-blooded and hatch from eggs. Since birds are warm-blooded, meaning that they maintain a constant internal body temperature despite the temperature of their environment, they are able to live in a wide variety of climates and environments. Unlike cold-blooded animals, they do not have to slow down their activity when the temperature drops. Compared to almost any other animal, birds use up an enormous amount of energy and have a very high rate of metabolism (which could be described as the rate at which their internal motor is running). This is because flying is such a high-energy activity. Since they have a high-energy lifestyle, birds have a high-energy diet (such as seeds, worms, fruit, meat, fish) and do not eat many low-energy foods like grasses or leaves.

Birds reproduce sexually and lay eggs (one at a time) from which their young hatch. Birds don't give birth to live young since weight is so critical, and flying while carrying a developing embryo inside would probably be impossible for a female. Bird eggs contain a yolk that feeds the embryo. They are covered by a hard shell, and one or both parents must keep them warm with their own bodies for them to develop and hatch. At birth, many birds are helpless and must be fed and cared for. While they may learn certain things from the behavior of their parents, important activities like flying and migrating are instinctive.

BIRDS BODIES ADAPTED TO FLIGHT

As a bird's feathers are perfectly adapted to flight, so too is the rest of its body built to give it the two things it needs to fly: low weight and high power. Compared to almost any other animal, a bird's skeleton makes up only a small percentage of its total weight. This is because its bones are hollow, or in fact, filled with tiny air spaces. Despite this, the bird has a very strong frame since many bones that are separate in other animals are fused in birds. Other systems conserve weight as well. A bird has no separate bladder (which would fill and add weight), but rather passes its nitrogenous waste along with its intestinal waste in a single pastelike form called bird droppings. Birds get their flying power from powerful breast muscles, and are able to feed these important muscles all the oxygen they need because of their highly efficient respiratory systems (which can also store air). Birds, like mammals, also have a four-chambered heart which keeps oxygen-rich blood from the lungs separate from the blood that is returning from the rest of its body. This guarantees that the muscles get as much oxygen as they need. Birds also have an above-average nervous system since they must perform highly coordinated movements in order to fly. They also have very sharp eyesight and good hearing.

As with insects, flight provides birds with a competitive advantage. They are able to escape quickly from an earthbound predator who cannot pursue them. Birds are also able to move to another habitat if food becomes scarce. Many birds do this annually as a regular part of their life cycle in a process called migration. Some birds make this an entire way of life, migrating as much as 25,000 miles (40,225 kilometers) in one year.

THE IMPORTANCE OF BIRDS

Birds play an important role in the ecosystem (an area in which living things interact with each other and the environment). They not only provide people with food (like chicken), but they consume an enormous quantity of insects and play a major role in pollination (the transfer of male pollen to the female part of a flower). Finally, birds make sounds that people find pleasant. Bird sounds are both calls and song, with the former used to communicate with others, and the latter used mainly to attract a mate.