New World vultures

(Cathartidae)

Class Aves

Order Ciconiiformes

Suborder Cathartae

Family Cathartidae

Thumbnail description
Medium large to very large, highly social birds that feed primarily on carrion with very few or no feathers on their heads; plumage color is generally black, gray, or brown with some portion of white in three of the largest species

Size
2.2–33.1 lb (1–15 kg)

Number of genera, species
5 genera; 7 species

Habitat
Forests, savannas, woodland, pastures, mountains, deserts, river ways, and seashores

Conservation status
Critically Endangered: 1 species; Near Threatened: 1 species

Distribution
Southern Canada to Tierra del Fuego

Evolution and systematics

The Cathartidae include seven species of vultures that range exclusively in North and South America. Also referred to as "Neotropical" or New World vultures, they were once thought to be closely related to Old World vultures, found in Europe, Asia, and Africa, but any similarities of the two groups can best be attributed to convergence or parallel evolution.

As recently as the last quarter of the twentieth century it was argued successfully on the basis of physiology, behavior, and genetics, that the cathartid vultures are not descended from the Accipitidiae as is accepted for the Old World vultures, but descended instead from a common ancestor with the Ciconidae, or storks. For instance, all of the cathartids and ciconids use "urohydrosis" or the method of cooling themselves by emitting liquid waste on the bare portion of their legs where densely packed blood vessels close to the skin are cooled by evaporation and, in turn, body core temperature is reduced. They also never rest on one foot as do birds of prey but instead lie down. While both New and Old World vultures express a distinct social hierarchy, that of Old World vultures is based more on the hunger level of a bird arriving at a carcass while the social status of New World vultures is based primarily on an individual's personal status that is determined by the individual's species, age, sex, and experience.

The evolutionary history of the Old and New World vultures is comparatively good. The earliest New World vulture was reported in England dating from late Paleocene deposits. Several "cathartid type" fossils are known from middle and late Eocene deposits in France and Germany but no remains after early Miocene have been located in the Old World. Fossil records show the New World vultures first appearing in America in the early Oligocene, flourishing along side Old World type vultures that became extinct toward the end of the Pleistocene, only 10,000–20,000 years ago. When the mass mammalian extinctions occurred, both Old and New World type vultures followed the fate of their prey.

The California condor appears to be the only large vulture to survive. Its Pleistocene range that spanned southern North America and included both coasts, was reduced to the west coast from British Columbia to northern Baja by modern times. Like the Andean condor today, it relied heavily on carrion found along the coast.

Physical characteristics

The family Cathartidae consists of five genera with seven species. The smallest species, by weight, is the 2.1 lb (0.94 kg) lesser yellow-headed vulture (Cathartes burrovianus). The other two species in the genus Cathartes, the turkey vulture (C. aura) weighing 3.3 lb (1.5 kg) and the greater yellow-headed vulture (C. melambrotus) at 2.6 lb (1.2 kg), are not much heavier yet all give the appearance of being much larger than their actual weight. The physical effect of their large flying surface area to weight ratio, called a "light wing loading," makes these three species comparatively more buoyant in air and able to take advantage of the slightest thermal to stay aloft close to the ground. The black vulture (Coragyps atratus) on the other hand has a relatively short wingspan, or flying surface, for its heavier weight of 4.4 lb (2.0 kg). These flight characteristics join with other behavioral and anatomical factors to help define niche separation in each species of this scavenger guild. The colorful king vulture (Sarcoramphus papa) is built more like a black vulture but larger, weighing about 7.5 lb (3.4 kg). The California condor (Gymnogyps californianus), like the smaller vultures, is sexually monomorphic in size and color, but is much heavier weighing 17–24 lb (7.7–10.9 kg) with a wingspan of 114 in (290 cm). The Andean condor (Vultur gryphus) is one of the largest flying birds in the world. It is sexually dimorphic in shape, color, and size. Females range in weight from 18 to 23 lb (8.3–10.5 kg), have dark gray skin on the head which has no caruncle, similar to the male. Their iris color in the adult is a deep red while that of the male is tan, plumages are the same. The larger male ranges from 24 to 33 lb (10.9–15 kg).

While the Cathartidae have only a rudimentary syrinx and cannot call or sing as other birds can they are able to communicate with a suprising array of grunts, growls, and hisses.

Distribution

The most widely distributed cathartid species is the turkey vulture, ranging from the Canadian border to the southern end of South America. There are also four subspecies of turkey vultures usually recognized based on slight differences in head color and distribution. The most migratory appears to be C. aura aura which has been extending its summer breeding range over the last few decades north though New England. It spends winters from the southern United States to northern South America competing with the more sedentary subspecies of that region. The movement patterns of the other cathartid species appear to be less latitudinally migratory but are more regional, associated with weather patterns, food supply, and breeding season.

Roosting areas are particularly important in influencing the distribution pattern in these vultures particularly for the rarer, larger condors where roosting conditions are more specific. Where hundreds of black and turkey vultures may roost in particular groves of trees or on the supports of man-made towers, it is more difficult for condors to find appropriate cliff roosts with the right climatic conditions. Dozens of condors may use a network of these traditional roosts as secure bases from which to forage in a particular area and they are as important

as adequate nesting sites in delineating the distribution of these vultures.

Habitat

From the northern to southern portions of where cathartid vultures range they are found in every habitat where their carrion food supply can be effectively exploited, including but not limited to deserts, coastlines, water ways, open grasslands and savannas, forests, cities, and mountain and canyon regions.

Unlike Old World vultures that do not forage in closed forests, three cathartid species in the New World are well adapted to successfully exploit forest as well as open habitat. They accomplish this through a sense of smell that is so acute they can find even small bird, reptile, and mammal carcasses in a forest shortly after they begin to decompose. Both condor species use winds generated off mountain slopes and thermal activity to move distances of hundreds of kilometers at thousands of meters of altitude within a few days covering several habitat types.

Behavior

New World vultures are highly gregarious roosting nightly and foraging communally by day. Unless there is already wind, in which case they can and will fly before dawn, vultures and condors typically wait until later in the morning when rising thermals can assist soaring flight to where the most recent carcass is located. When the first rays of sun hit the roost or throughout the day when it peaks from behind a cloud, vultures will spread their wings and orient themselves at right angles to the sun. Seen also after bathing, this pose, called sunning, dries and straightens flight feathers and functions to assist with preening in reducing ectoparasites.

Like the accipitrid vultures in Africa, the Cathartidae partition the food resources of the available carrion in an area through timing, anatomical differences, and a relatively ordered hierarchy. Black vultures, with a heavier wing loading, are most efficient at foraging when flying at higher altitudes where they can best observe the behavior and activities of their own and other species. Lacking the ability to use olfaction, like the three smaller Carthartes species, they rely on vision to hunt. When flying conditions allow, a foraging flock of black vultures will disperse over miles, where they can effectively scan for resource opportunities to exploit over a large area. When activity of interest is noted by one or more individuals, the adjusted flying pattern appears to signal the attention of other flock mates. As more and more birds gather over a carcass, the inadvertent signal produced by the mass of large black birds at varying altitudes can persist over many days attracting the larger, less common species of scavengers such as king vultures and Andean condors. The same scenario is carried out on the west coast of North America involving turkey vultures, ravens, and California condors.

Where black vultures occur, their population levels can get quite large, even into the thousands sustained by some type of consistent and predictable food source like a city dump. So behaviorally astute are black vultures that they will adjust their flight distance to humans depending on the circumstances. The same marked bird feeding without fear within a few feet of people at the Panama City market place one day will flush away the next day when approached within 164 ft (50 m) in the countryside. When black vultures first arrive at a natural carcass, not part of the usual system, they have usually followed one of the Cathartes species. At low, equal numbers, black vultures generally cannot dominate turkey vultures, but as their group size increases, the Cathartes species often move to the side of the main feeding activity or leave altogether.

Feeding ecology and diet

King vultures, and especially condors, can go longer periods between meals than the smaller vultures as long as water is available. Reintroduced California condors re-trapped after 26 days of unsuccessful foraging showed no behavioral or clinical signs of stress. They generally fly higher, faster, and over larger areas, foraging away from roost site and nesting territories. When they arrive at a carcass, they dominate any of the smaller species. Observations of marked wild Andean condors indicate that birds with high status are less reluctant to approach the carcass. The smaller bills of the Cathartes and Coragyps vultures are not sufficient to tear through the hide of large carcasses and usually are confined to natural openings of the mouth, eyes, ears, and anus. Three to five of the most dominant individuals of the 100 member black vulture flock can defend the few holes in a fresh, large carcass. Sometimes hundreds of birds wait off to one side for the social dynamics to change. When condors or even king vultures arrive, the waiting, lower status vultures become alert and begin to crowd the carcass as the first condor approaches. With a bill every bit as powerful as the largest Old World vulture, one or more condors soon open several access points in the tough hide, making it difficult or impossible for a few dominant black vultures to successfully defend the carcass. With a breakdown in the hierarchy, a feeding frenzy ensues and even young, normally submissive birds can race into the confusion and successfully dash out with food.

Reproductive biology

The black vulture and the three Cathartes species all lay three eggs on a yearly basis. Although sexually mature by age two they may take several more years to acquire a mate and successfully breed. The king vulture and the two condors lay only one egg per season. Condors have a very slow reproductive rate and may take two or more years to produce one young. Parental dependence is months long in the larger species but short to non-existent in the genus Cathartes possibly due to their almost immediate success at finding food through olfaction. Monogamy is typical, with pair bonds that are life long, but shifts in mates may occur if the pair is unproductive over several years. Territory defense in condors is males against intruding males and females against females.

Conservation status

Where turkey vultures and black vultures are gradually expanding their range in some areas, the king vulture and condors have had significant declines. The California condor that narrowly escaped extinction at the end of the Pleistocene had been declining since the early 1800s when the growing human population reduced its coastal food supply and directly shot and poisoned the species. By the early 1980s, only 21 had survived and by 1987 all of the wild flock had to be brought into captivity to insure the species survival. Captive breeding programs at the Los Angeles Zoo and the San Diego Wild Animal Park and later, the World Center for Birds of Prey in Idaho have been highly successful in producing numbers of birds while preserving the remaining founding genetic lines. The reintroduction of the species into its former habitat began in 1992 and by the close of 2001 there were 183 birds with nearly 60 of those in the wild at three release sites; two in California and one in Arizona. Attempts to breed in the wild began in 2002. Andean condors have also been reintroduced into parts of their former range where they had been extirpated. North American Zoos, through their Species Survival Plan for Andean Condors, raised and released over 80 Andean condors in Venezuela and Colombia where they now breed in the wild.

Significance to humans

Condors were important in the mythology and featured in the rituals of the pre-Columbian cultures in the Andes. Their image is found incorporated in the textile designs, pottery, and carvings of these peoples. Even today the Andean condor appears on the coats of arms of Colombia, Bolivia, Ecuador, and Chile. Native North American groups greatly respected the California condor. It was buried with the dead, and its image was incorporated into their artistic motifs.

Many early human cultures associated vultures with death and these birds became important symbols in burial rituals. Today vultures are not respected as they were by earlier cultures, but they are tolerated for the valuable environmental service they provide. Vultures have suffered in recent years from human-generated pollution. Positioned as they are at the end of the food chain, vultures are likely to accumulate toxins and contaminants, which can kill them outright or damage their reproductive success. Other human-made hazards, such as power lines, can also pose a danger to flying birds.

Species accounts

List of Species

Turkey vulture

Cathartes aura

subfamily

Catharnae

taxonomy

Vultur aura Linnaeus, 1758, Veracruz, Mexico. Four sup-species.

other common names

French: Urubu à tête rouge; German: Truthahngeier; Spanish: Aura Gallipavo.

physical characteristics

Depending on race 1.9–4.4 lb (0.85–2 kg); 25.2–31.9 in (64–81 cm); sexually monomorphic. Brownish black plumage with bare head and neck; skin color varies from pink to bright red.

distribution

Southern border of Canada in North America to Tierra del Fuego, Chile, winter migration from northern portions of

United States to Central America and north and central South America. Has been expanding its range north over the last three decades.

habitat

Woodland, savanna, desert, and seashore.

behavior

Roosts socially and hunts for carrion in small groups or singly using olfaction. Lowest status at large carcasses generally sub-ordinate to larger vultures. When caught will regurgitate and feign death.

feeding ecology and diet

Will feed on dead animals of any size but specializes on smaller carcasses found by relying on olfaction. Has been seen to feed on rotten fruit and vegetables.

reproductive biology

Two eggs are brown blotched over a cream base; nests in shallow cave, on the ground in dense vegetation, or in hollow log; 38–41 days of incubation. Both parents tend eggs and young. Chick "down" color white gradually changing overall to dark brown as contour feathers emerge. Fledging from nest area at about 67 days with a relatively short parental dependency period of a few weeks.

conservation status

Not threatened. Populations seem stable in most areas unless roost trees are destroyed. Expanded use of road kills and laws against shooting large birds are possible reasons for recent northward expansion.

significance to humans

Never used as food.

Lesser yellow-headed vulture

Cathartes burrovianus

subfamily

Catharnae

taxonomy

Cathartes burrovianus Cassin, 1845, near Veracruz City, Mexico. Two subspecies sometimes recognized.

other common names

English: Savanna vulture; French: Urubu à tête jaune; German: Kleiner Gelbkopfgeier; Spanish: Aura Sabanera.

physical characteristics

Smallest of the Cathartes on average, 23–26 in (58–66 cm),2.1–3.3 lb (0.94–1.5 kg); sexually monomorphic. Black plumage; bare skin on head and neck varies from bright yellow to orange and blue tones.

distribution

South Central America to Uruguay, east of the Andes Mountains.

habitat

Open savanna and water courses, open flat grasslands to the edge of forest but generally not over forest.

behavior

Uses olfaction as other members of its genus.

feeding ecology and diet

Will feed on dead animals of any size but specializes on smaller carcasses found by relying on olfaction.

reproductive biology

Very little known but that in general it is similar to C. aura.

conservation status

Status and distribution poorly known but not threatened.

significance to humans

Never considered food. Like other small vultures generally tolerated because of feeding habits that reduce the presence of animal carcasses decreasing the likelihood of disease transmission to humans.

Greater yellow-headed vulture

Cathartes melambrotus

subfamily

Catharnae

taxonomy

Cathartes melambrotus Wetmore, 1964, Kartabo, Guyana. Monotypic.

other common names

English: Forest vulture; French: Grand urubu; German: Großer Gelbkopfgeier; Spanish: Aura Selvática.

physical characteristics

29–32 in (74–81 cm), 2.6–3.6 lb (1.2–1.65 kg) but with larger wings than the heavier C. aura. Similar head color to C. burrovianus.

distribution

Not well known. Southern Venezuela and the Guianas and other parts of Amazonia.

habitat

Typically low tropical forest and less inclined to use open or disturbed forest.

behavior

Uses olfaction as other members of its genus.

feeding ecology and diet

Specializes on smaller carcasses found in forested areas by relying on olfaction.

reproductive biology

Not known, but probably similar to C. avra in most respects.

conservation status

Status and distribution poorly known but in undisturbed forests can be common.

significance to humans

None known.

American black vulture

Coragyps atratus

subfamily

Catharnae

taxonomy

Vultur atratus Bechstein, 1793, St. John's River, Florida. Three subspecies.

other common names

English: Black vulture; French: Urubu noir; German: Rabengeier; Spanish: Zopilote Negro.

physical characteristics

22–27 in (56–69 cm), 2.4–4.2 lb (1.1–1.9 kg). Entirely black with light gray ventral wing patches at the base of the primary feathers. Sexes alike. Smooth dark gray head skin of young birds becomes fleshy and warty with age.

distribution

Southern North America to southern South America.

habitat

Open areas and water ways.

behavior

Roosts, forages and feeds more socially than other species of Cathartidae except for the condors. Flocks at roosts can number several hundred. Heavy wingloading causes tendency to fly at higher altitudes and flap more compared to Cathartes species. Most gregarious of the species.

feeding ecology and diet

Will feed on dead animals of any size. Have been known to kill injured or highly compromised animals on rare occasions. Finds carcasses by observing the behavior of other species and checking areas where food was historically more predictable. Cannot use olfaction as can members of the genus Cathartes, relies primarily on sight.

reproductive biology

Two brown mottled eggs laid in darkened sheltered cave, thick vegetation, or abandon buildings. No nest material used. Incubation takes 38–45 days. Chicks covered with reddish brown down; fledging at about 90 days. Extended parental dependency of several months.

conservation status

Not threatened. Common in most areas of its range.

significance to humans

Never considered food. Like other small vultures generally tolerated because of feeding habits that reduce the presence of animal carcasses decreasing the likelihood of disease transmission to humans.

King vulture

Sarcoramphus papa

subfamily

Catharnae

taxonomy

Vultur papa Linnaeus, 1758, Suriname. Monotypic.

other common names

French: Sarcoramphe roi; German: Königsgeier; Spanish: Zopilote Rey.

physical characteristics

28–32 in (71–81 cm), 6.6–8.3 lb (3–3.8 kg). Most brilliantly colored of the New World vultures with varying hues ranging from purple and blue to red and orange on its head. Its contrasting black and white plumage is opposite that of condors, with a white body and black primary and secondary wing feathers.

distribution

Southern Mexico to northern Argentina.

habitat

Usually associated with lowland tropical forests but can also be found in savannas, grasslands, and desert margins.

behavior

Seldom seen in large groups, usually visits carcasses as a pair with their single offspring where they easily dominate the smaller vultures. Forages for food at high altitudes. They are less gregarious and roost in pairs or family threesomes.

feeding ecology and diet

Has no apparent sense of smell and finds carcasses through the activities of other vultures. Its bill, which is more powerful than the bills of the smaller cathartids, enables it to feed more easily on large carcasses.

reproductive biology

Territorial pairs lay a single white egg in hollow trees, sometimes high off the ground. As with other carthatids, no nesting material was used in the few nests that have been found. The 53–58 day incubation is shared equally by both sexes, as regularly seen in captivity. Down of young chick is white. Fledging is at three months with an extended parental dependency period of several more months.

conservation status

CITES III status in Honduras, but not globally threatened. Relatively rare compared to smaller vultures, but appear to be naturally uncommon even in undisturbed forests.

significance to humans

Indigenous cultures depicted this striking species in artwork.

California condor

Gymnogyps californianus

subfamily

Catharnae

taxonomy

Vultur californianus Shaw, 1798, Monterey, California. Monotypic.

other common names

French: Condor de Californie; German: Kalifornischer Kondor; Spanish: Cóndor Californiano.

physical characteristics

46–53 in (117–134 cm) 17–24 lb (7.7–10.9 kg). Wingspan of nearly 10 ft (3 m). Entirely black plumage except for conspicuous triangle of white feathers in the ventral portion of both wings in the adult. The grayish triangle of juvenile birds gradually becomes whiter by five years of age. The grayish head color of the juveniles also gradually changes to reddish orange as they mature.

distribution

While the species once ranged from British Columbia to northern Baja in the early 1800s, it became extinct in the wild in 1987. As a result of reintroduction efforts, its 2002 range includes the coastal mountains in California from Monterey to just north of Los Angeles, and a disjunct population north of the Grand Canyon in Arizona.

habitat

Roosting and nesting occur in mountainous areas where winds allow the birds to range widely. Foraging occurs in open areas of savanna, grasslands, and coastal beaches where food is located through the activities of other scavenger species.

behavior

Highly curious and intelligent, it finds food through observing the behaviors and activities of other species. Condors can travel hundreds of miles in a single day, foraging alone or in well dispersed groups at high altitudes. Strict hierarchy at a carcass reduces aggression to a minimum.

feeding ecology and diet

Scavenger of large carcasses that include marine mammals as well as wild and domestic ungulates. Their large and powerful bill enables them to tear open thick hide.

reproductive biology

Courtship displays generally begin in October with egg laying beginning in mid-January to late April. The single white egg is incubated equally by both parents through its 57 day incubation period. The chick takes about six months to fledge, with a lengthy parental dependency period that appears to vary with food availability. Sexual maturity is at five to six years of age. Pair bonds are for life as long as the pair remains productive.

conservation status

Critically Endangered. Wild population was as low as 19 birds. In 1987 the remaining birds were brought into captivity to re-build the population. Through strict out-breeding of pairs within the 14 family lines and multiple clutching techniques, the species has rebounded to 183 birds by the end of 2001.

significance to humans

Native American cultures along the California and Oregon coasts have had a long and intimate history with this species. They have used feathers and bones for ceremonies, depicted the birds in artwork, and incorporated them in their legends.

Andean condor

Vultur gryphus

subfamily

Catharnae

taxonomy

Vultur gryphus Linneaus, 1758, Chile. Monotypic.

other common names

French: Condor des Andes; German: Andenkondor; Spanish: Cóndor Andino.

physical characteristics

39–51 in (100–130 cm) 18.1–23.1 lb (8.2–10.5 kg). with a wingspan of as much as 10 ft (3 m). Black plumage with large white patches on the dorsal portion of the wings. Neck ruff of short white feathers. Sexually dimorphic with males exhibiting a large fleshy crest, tan-colored irises, and head skin ranging from dark gray to yellow. Females have red irises, grayish skin on their head, and can be 2.2–11 lb (1–5 kg) lighter.

distribution

Andes Mountains from Venezuela to Tierra del Fuego, ranging to the coast from northern Peru to southern Chile and Argentina.

habitat

Roosting and nesting occur in mountainous areas where winds allow the birds to range widely. Foraging occurs in open areas of savanna, grasslands, deserts, and beaches along the coast.

behavior

Highly curious and intelligent, it finds food through observing the behaviors and activities of other species. Condors can travel hundreds of miles in a single day, foraging alone or in well dispersed groups at high altitudes. Strict hierarchy at a carcass reduces aggression to a minimum. At Andean condor roosts in South America, groups consisting of several immature birds seem to gain the same information advantage as in the black vulture system. In areas where large roosts are not convenient, however, juvenile bands move between territory pairs led by the older more experienced individuals of the group. Their brown, immature stage plumages, which gradually change to black and white by seven years of age, afford them safe passage between nesting cliffs defended against adults and gain them the advantages of associating with knowledgeable adult birds.

feeding ecology and diet

Scavenger of large carcasses that include marine mammals as well as wild and domestic ungulates. Have been known to feed on sea bird nestlings on offshore guano islands. Their large and powerful bills enable them to tear open thick hide.

reproductive biology

Courtship displays have been seen throughout the year near the equator. To the far south nesting occurs from May through August. Incubation from 58 to 62 days (captive) and fledging takes about six months. While pairs may hold territories, nesting may occur every other year and may be postponed for several years if food availability is low. Parental dependency period is lengthy and may vary with food supply.

conservation status

Listed as Near Threatened but still abundant in the Chile/Argentina Andes where thousands of birds exist. Fewer birds as one progresses north along the Andes until Colombia and Venezuela where the population consists of mostly reintroduced birds.

significance to humans

Pictographs and legends found throughout native cultures. "The sun rose and set by the wings of the condor," according to an Inca belief. Festivals and rituals involving this species still exist. A modern Andean festival involves tying a condor to a bull's back and sending the bull running through the town. If the condor survives, it symbolizes the successful resistance of the native South Americans against the Spanish conquistadors, and it is released back to the wild.

Resources

Books

Blake, E.R. Manual of Neotropical Birds. Vol. 1: Spheniscidae (Penguins) to Laridae (Gulls and Allies). Chicago & London: University of Chicago Press, 1977.

Snyder, N.F.R., and H.A. Snyder. Birds of Prey: Natural History and Conservation of North American Raptors. Stillwater, Minnesota: Voyageur Press, 1991.

Wallace, M.P., and W. Toone. "Captive Management for the Long Term Survival of the California Condor." In Wildlife 2001: Populations, edited by D. R. McCullough and R.H. Barrett. Elsevier Applied, 1992.

Wilbur, S.R., and J.A. Jackson, eds. Vulture Biology and Management. University of California Press, 1983.

Periodicals

Audubon, J.J. "Account of the Habits of the Turkey Buzzard Vultur aura Particularly with the View of Exploding the Opinion Generally Entertained of Its Extraordinary Powers of Smelling." Edinb. New Phil. Journal 2(1826):172–184.

Bang, B.G. "The Nasal Organs of the Black and Turkey Vultures: A Comparative Study of the Cathartid Species Coragyps atratus atratus and Cathartes aura septentrionalis (With Notes on Cathartes aura falklandica, Pseudogyps bengalensis and Neophron percnopterus)." Journal of Morphology 115(1972): 153–184.

Bernal, L.G., D.C. Houston, and P. Cotton. "The Role of Greater Yellow-headed Vultures as Scavengers in Neotropical Forests." Ibis 136(1994).

Clinton-Eitniear, J. "King Vulture Research Report." Vulture News 6(1981):7–8.

Cox, C.R., V.I. Goldsmith, and H.R. Engelhardt. "Pair Formation in California Condors." Amer. Zool. 33(1993): 126–138.

Davis, D. "Morning and Evening Roosts of Turkey Vultures at Malheur Refuge, Oregon." Western Birds 10(1979): 125–130.

Gailey, J., and N. Bolwig. "Observations on the Behaviour of the Andean Condor Vultur gryphus." Condor 75(1973):60–68.

Graves, G.R. "Greater Yellow-headed Vulture (Cathartes melambrotus) Locates Food by Olfaction." Journal of Raptor Research 26(1992): 38–39.

Houston, D.C. "Competition for Food Between Neotropical Vultures in Forest." Ibis 130(1988): 402–417.

Kiff, L.F. "An Historical Perspective on the Condor." Outdoor California 44(1983): 5–6, 34–37.

Kiff, L.F. "To the Brink and Back: The Battle to Save the California Condor." Terra 28(1990): 6–18.

Meretsky, V., and N.F.R. Snyder. "Range Use and Movements of California Condors." Condor 94(1992): 313–335.

Pattee, O.H "The Role of Lead in Condor Mortality." Endangered Species Bulletin Vol. 12, No. 9 (1987): 6–7.

Rabenold, P.P. "Family Associations in Communally Roosting Black Vultures." Auk 103(1986): 32–41.

Snyder, N.F.R., R.R. Ramey, and F.C. Sibley. "Nest Site Biology of the California Condor. " Condor 88(1986): 228–241.

Snyder, N.F.R., and H.A. Snyder. "Biology and Conservation of the California Condor." Current Ornithology 6(1989): 175–267.

Stewart, P.A. "The Biology and Communal Behaviour of American Black Vultures." Vulture News 9/10(1983): 14–36.

Toone, W., and A.C. Risser. "Captive Management of the California Condor Gymnogyps californianus." International Zoology Yearbook 27(1988): 50–58.

Michael Phillip Wallace, PhD