GULLS, TERNS, PLOVERS, AND OTHER SHOREBIRDS: Charadriiformes

PHYSICAL CHARACTERISTICS

Birds of the order Charadriiformes range in size from 0.06 to 4.4 pounds (25 grams to 2 kilograms). They vary greatly in body length, body shape, leg length, and bill shape, making generalizations about their physical characteristics difficult.

GEOGRAPHIC RANGE

Charadriiforms are found worldwide, including all seven continents.

HABITAT

Species in the order Charadriiformes occupy diverse habitats. They are generally found near water, whether coastal, inland, or on the ocean. Many charadriiforms inhabit wetland areas, both marine and freshwater. Others spend large amounts of time in or near the ocean.

DIET

As a group, charadriiforms range greatly in their diet and feeding strategies. Because of their use of aquatic habitats, many Charadriiformes species eat primarily fish. Among the fish-eaters, there are various methods for pursuing prey. The terns, for example, dive from the air into water to catch fish near the surface of the ocean. Alcids (auks, puffins, and murres) are good swimmers and swim underwater after their prey. Skimmers fly low over the water and scoop up fish from near the surface.

Other Charadriiformes have a diet formed primarily of insects and other invertebrates. Plovers search for insects and other prey using their eyes, and then pick them from the ground with their short bills. Most sandpipers, on the other hand, rely largely on the sense of touch, using their long, sensitive bills to locate prey hidden in mud.

Plants and other vegetable matter form an important part of the diet of some Charadriiformes species as well. Sheathbills, for example, eat large amounts of algae (AL-jee). Plains-wanderers eat primarily seeds. Seed-snipes, despite their name, eat primarily buds, leaf tips, and small green leaves.

BEHAVIOR AND REPRODUCTION

Some species of Charadriiformes do not migrate, remaining instead in the same area throughout the year. Other charadriiforms, however, do migrate, traveling from one area to another and back during the course of the year. Migrations generally occur between breeding grounds in the spring or summer and wintering grounds. Among the charadriiforms, shorebirds and terns are particularly well-known for their long, difficult migrations. The Arctic tern travels more than 18,000 miles each year (28,960 kilometers) between its breeding areas in the Arctic and its wintering areas in the Southern Hemisphere. The Pacific golden plover migrates between Alaska and Hawaii, a distance of 2,200 miles (3,540 kilometers), in less than two days.

Many species of charadriiforms can be found in large flocks, either during the breeding or winter season. Gulls, terns, and alcids are regularly found in groups as large as a hundred thousand individuals during the breeding season. Even larger collections of charadriiforms are found during migrations, or during the winter. In the Copper River Delta in Alaska, as many as five million shorebirds may be seen during their spring migration.

COLONIAL NESTERS

Colonial nesters are species in which large numbers of individuals build their nests and raise their young in a single location. Among the Charadriiformes, the gulls, terns, and alcids are particularly known for their colonial nesting habits. During the breeding season, colonies can range in size from several hundred individuals to as many as hundreds of thousands of birds. Charadriiformes are able to gather in such large numbers because the habitats they prefer tend to be extremely rich with food resources.

The majority of Charadriiformes species are monogamous (muh-NAH-guh-mus), meaning that a single male mates with a single female during the breeding season. In some species, individuals keep the same mate from one breeding season to the next. In monogamous Charadriiformes, both male and female help defend the nest and take care of young chicks once they hatch. Other charadriiforms have more unusual breeding systems. The jacanas are polyandrous (pah-lee-AN-drus), with a single female mating with multiple males. Still other charadriiforms, such as many species of sandpipers, are polygamous (puh-LIH-guh-mus), with a single male mating with multiple females.

Charadriiformes tend to build fairly simple nests, often just a hollow in the ground lined with a few pebbles or pieces of vegetation. Some charadriiform seabirds nest in rocky cliff areas, and lay their eggs directly on rock ledges without building any nest at all. The other end of the spectrum, some murrelets and sandpipers build nests in trees or use nests that have been built and abandoned by other bird species. Generally, females lay between one and four eggs at a time. Eggs hatch after a period of three weeks or longer. Some Charadriiformes, including most shorebirds species, have precocial chicks. These hatch at a fairly advanced stage of development, covered with down and able to move. Precocial chicks are usually able to leave the nest soon after they hatch. Others, such as most seabirds, have altricial chicks, which hatch at a less developed state. These hatch blind and without feathers, and usually stay in the nest for a longer period of time.

GULLS, TERNS, PLOVERS, OTHER SHOREBIRDS, AND PEOPLE

Humans have hunted many species of charadriiform birds for meat, feathers, oil, and eggs. Because Charadriiformes are often found in large flocks during breeding, migration, or the winter season, they have frequently made easy targets for hunters. For example, between 1988 and 1989 alone, some 300,000 to 400,000 thick-billed murres were killed in Greenland.

HUNTERS AND CHARADRIIFORMES

Because different species of Charadriiformes gather in large numbers during breeding, migration, or wintering seasons, they are frequently attractive targets for hunters. Many species have been hunted for their meat, feathers, oil, and eggs. Hunting by humans is believed to have resulted in the extinction of at least two Charadriiformes, the Eskimo curlew and the great auk. Hunting continues to contribute to the threatened state of many other charadriiform species.

CONSERVATION STATUS

Of the 343 species of Charadriiformes, thirty-four are currently considered Threatened, in danger of extinction, by the World Conservation Union (IUCN). Threatened species have been affected by habitat destruction and damage (particularly in wetland areas as well as rivers and streams), pollution, hunting, and other factors. Some species have declined as over-fishing by humans eliminates important seabird prey populations. Finally, certain Charadriiformes species are periodically devastated by large oil spills.

FOR MORE INFORMATION

Books:

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.

Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.

Web sites:

The Internet Bird Collection. http://www.hbw.com/ibc/phtml/families.phtml (accessed on April 15, 2004).

"Order Charadriiformes (Shorebirds and Relatives)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/classification/Charadriiformes.html (accessed on April 15, 2004).

"Birds of the World." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/families.htm (accessed on April 15, 2004).