Photo: Raul Vega.
This article is about the biology, ecology, natural history, and conservation of vultures in North, Central, and South America. These include Greater Yellow-headed Vulture, Lesser Yellow-headed Vulture, Turkey Vulture, American Black Vulture, King Vulture, Andean Condor, and California Condor.
Table of Content
Vultures are scavengers. In urban culture, “a vulture” is a person or business who hovers to prey on the misfortune of others. This derives from the fact that vultures are often seen hovering in the sky, seemingly searching for dead animals or congregating around a dead animal on roadsides.
Vultures in North, Central, and South America
The vultures that occur in North, Central, and South America (or vultures of the New World) are not related to vultures in the Old World (Africa, Asia, and Europe). Both groups of vultures may have a similar appearance, but they come from completely different ancestry.
The scope of this article is limited to the vultures of North, Central, and South America.
There are 15 species of Old World Vultures and 7 species of New World Vultures.
All vultures look alike and feed almost entirely on dead animals. The reason for this resemblance is the result of ecological convergence.
Let me explain.
Vultures in both worlds specialize in a similar feeding behavior doing basically the same things. As a result, both groups of carrion-eating birds developed similar morphology and behavior without having a common ancestor.
Both vulture groups have a strong hooked bill to tear meat, a bare head and neck to avoid soiling its feather while reaching for the meat inside carcasses, and long and broad wings to effortlessly cover extensive areas in search of food using thermal up currents without spending much energy.
Both groups of vultures have two key differences.
- New World vultures have a non-function hind toe. While the hind toe is there, vultures are unable to grab and carry anything with their feet.
- Another difference is that the New World vultures do not have a separation between the nostrils. The nostrils have only a bridge on top and one can see through.
Ecological Function of Vultures
Because vultures are associated with dead animals and garbage, their reputation is not the best. However, vultures play an essential role in nature. They quickly and efficiently consume dead animals that might have died from a disease-preventing such disease from spreading and affecting other animals.
Vultures have developed immunity to many diseases and are not affected by diseases that kill other animals.
In Amazonian cities in Latin America, the role of vultures is crucial. With hot temperatures and high humidity, the smell of dead animals and the risk of disease spreading are real threats to humans and wild and domestic animals. A large number of vultures in the region consume tons of not only dead animals but also spoiled food and meat scraps.
New World Vultures
They are different in appearance, body size, foraging behavior, and the type and manner they consume meat.
Turkey Vulture
- Length: ~72 cm (~28.3 in)
- Wingspan: ~171 cm (~67 in)
- Weight: 1.4 kg (~3.1 lb)
- Clutch Size: 2 white eggs
- Incubation period: 40 days
- Sexual Maturity: 3 years
Brian Ralphs/Flickr/CC by 2.0
Greater Yellow-headed Vulture
- Length: ~70 cm (~28 in)
- Wingspan: 122 cm (~48 in)
- Weight: ~1.4 kg (~3.1 lb)
- Clutch Size: 2 white eggs
- Incubation period: Unknown
- Sexual Maturity: Likely 3 years
Bradley Hacker/Flickr/CC by 2.0
Lesser Yellow-headed Vulture
- Length: ~59 cm (23.2 in)
- Wingspan: ~157 cm (62 in)
- Weight: male 1.2 kg (2.6 lb), female 1.3 kg (2.8 lb)
- Clutch Size: 2 white eggs
- Incubation period: 40 days
- Sexual Maturity: Likely 3 years
Photo: Randall Jiménez Borbón.
Black Vulture
- Length: ~65 cm (~26 in)
- Wingspan: ~147 cm (~58 in)
- Weight: ~1.5 kg (~3.3 lb)
- Clutch Size: 2 pale blue eggs
- Incubation period: 42 days
- Sexual Maturity: Likely 3 years
Photo: Alejandro Tabini
King Vulture
- Length: ~76 cm (30 in)
- Wingspan: ~185 cm (73 in)
- Weight: ~3.3 kg (7.3 lb)
- Clutch Size: 1 white egg
- Incubation period: 56 days
- Sexual Maturity: 4 years
Photo: Raul Vega.
California Condor
- Length: ~122 cm (48 in)
- Wingspan: ~275 cm (108 in)
- Weight: ~11 Kg (24 lb)
- Clutch Size: 1 white egg
- Incubation period: 58 days
- Sexual Maturity: 6 years
Photo: Stacy/Flickr/CC by 2.0
Andean Condor
- Length: ~115 cm (45.3 in)
- Wingspan: 260-320 cm (102-126 in)
- Weight: Males ~13 kg (29 lb), Females: 9.5 kg (21 Lb)
- Clutch Size: 1 eggs
- Incubation period: 55 days
- Sexual Maturity: 6 years
Photo: Walter Baliero Carluccio.
Who are Vultures’ Closest Relatives?
It was long thought that vultures were closely related to hawks and eagles.
Despite vultures’ appearance and anatomical similarities to hawks and eagles, studies have found that vultures share similar skeletal and skull structures only with storks.
Vultures and storks also share a unique behavior. Both groups of birds squirt urine and feces onto their legs as a cooling mechanism. The liquid or runny urine on their legs absorbs heat during the process of evaporation, producing a cooling effect.
No other group of birds exhibits this behavior, further supporting the idea that storks and vultures are closer relatives than vultures are of eagles and hawks.
How are Vultures in North, Central, and South America Related?
Relatedness among New World vultures is actually poorly understood. The genus Cathartes, also referred to as Cathartid, includes the Greater Yellow-headed Vulture, Lesser Yellow-headed Vulture, and the Turkey Vulture; these species are closely related.
The American Black Vulture appears to be the odd relative. It has such a different morphology and behavior that it is difficult to ascertain which other new world vulture it is closely associated with.
The Andean Condor and the California Condor are among the largest flying birds and show superficial similarities. Both species are restricted to mountain ranges, but those are basically similarities. A more comprehensive look reveals that these two condors have very few physiological and structural similarities.
Although related, they separated from common ancestors millions of years ago. The two species of condors are in their own monotypic genera. The Andean Condor has a very marked sexual dimorphism, while the California Condor is more like other vultures with little or no sexual dimorphism.
The function of Bald and colorful heads in Vultures
It is broadly accepted that the featherless head of vultures keeps it free from soiling as they poke their heads inside carcasses.
Keeping the head clean may not be the only function. It is only the California Condor and the Black Vulture that poke their heads into carcasses. Other vultures exhibit this behavior.
There appear that the bald and colorful heads of vultures may have other functions.
The bright colors and folded skin in the head of vultures also appear to be used as social indicators of dominance and a mechanism to regulate body temperature.
The regulation of body temperature may be important, particularly in vultures of black or dark plumages. The bare skin of vultures has a high density of blood vessels. Birds appear to be able to increase and decrease blood circulation and change the color of their heads as they release or maintain heat.
The color and brightness of the vultures’ heads can also be used as social signals in courtship and confrontational displays.
Birds with bright colors may be older and in better physical form. These birds appear to rank higher in the hierarchy and have a higher priority when it comes to accessing meat at a carcass. A brightly colored head also gives clues about the health status of a bird, which may enable such a bird to obtain suitable mating partners.
Photo: Zweer de Bruin/Flickr/CC by 2.0
What is Vulture Habitat?
Vultures use a remarkable array of habitats. The two species of condors are large and heavy and need strong winds and up currents, as well as, cliffs to take off and soar without spending much energy. This appears to limit the range of condors to tall mountains such as those of the Andes of South America and the Sierra Nevada in the Western United States.
- The turkey vulture is perhaps the most successful of all vultures. It favors habitats ranging from very dense tropical forests to open country and sandy beaches.
- The Greater Yellow-headed Vulture is largely restricted to mature, undisturbed, and dense tropical forests.
- The Lesser Yellow-headed Vulture favors grasslands and Savannah habitats, as well as similar habitats along large Amazonian rivers. They do not enter dense forests.
- The American Black Vulture uses a variety of habitats but is largely associated with humans. Before the human expansion, this vulture was perhaps restricted to river edges and other open and semi-open habitats. As human settlements expanded, so did the habitat for the Black Vulture.
- The Andean Condor is largely restricted to the High Andes. They also descend to the Argentinian grasslands and coast of Peru and Chile, where strong and persistent winds allow them to glide and soar effortlessly.
- The King Vulture is largely restricted to mature and undisturbed tropical forests. It also uses semi-open woodland and savannah habitats that have pockets of forests.
- The California Condor is now restricted to the Sierra Nevada Mountain Range from its more extensive former range.
Do Vultures Migrate?
Little is known about the movements of the vultures in the Amazon basin. It is likely that birds move regionally within the region.
The Andean Condor is known to cover long distances within what could be a home range in a cyclical manner. Field observations suggest that birds that roost at known sites disappear for weeks and later reappear.
A study that used radio telemetry in sub-adult condors indicated that birds covered home ranges of hundreds of kilometers. Birds appeared to retrace the same routes continuously.
In Peru, the Andean Condor descends from the high Andes to coastal sites to consume the afterbirth of sea lions giving birth. After the sea lions were no longer giving birth and no longer cubs were dying, the number of Andean Condors in at coastal sites diminished considerably.
Perhaps the best-documented movement of any vulture is that of the sub-species of Turkey vulture (Cathartes aura aura). Birds leave North America in large flocks flying overland to the wintering grounds in Central and Northern South America and vice versa.
Energy Balance
Vultures live a life of uncertainty and must budget their energy expenditure. Because they feed largely on dead animals, food is distributed over large areas and is difficult to obtain.
Vultures have developed ways to cope with uncertainty. Studies have shown that Turkey Vultures have a slower metabolism than birds its size.
When food is available, vultures will consume as much food as they can handle and store body fat for times when food is scarce and must go through periods without food.
To reduce spending on energy, vultures have become masters of flight. They are very skillful at using thermal up currents that allow them to cover large areas soaring and gliding without spending unnecessary energy beating their wings.
Photo: Alvaro Castro.
Social Behavior
In general, vultures and condors are solitary birds except for the times they congregate around carcasses and during the breeding season as a mated pair. The exception to this is the American Black vulture, which often moves in loose flocks and roosts together in large numbers.
Studies have suggested that congregations of vultures at a roost site act as an information center.
Birds that were not able to find food one day will follow the successful birds as these leave the roost in the morning to a carcass or other feeding spot.
The California and Andean Condor are known to do the same in much smaller roosting flocks.
Vultures are known to stay together as a family group. Parents and juveniles may forage together for a year or so.
The King Vulture is often seen in pairs with one juvenile of the year on a carcass. Family groups often act together to protect a carcass from other vultures.
Care of the Plumage
Vultures must take care of their plumage as their livelihood depends on it. In particular, their flight feathers must be kept in good condition as they spend hours in the air searching for food.
They spend hours preening the contour or body feathers, rearranging them, and eliminating pieces of food that attach to the body.
Birds spend a considerable amount of time grooming their flight or wing feathers. Vultures open and maintain their wings open for some time in what is known as sunning behavior. They also open their wing during rainfall as a way of bathing. Then, they spend time combing and grooming each feather.
Keeping their wings open may have other purposes. It has been suggested that vultures spread their wings as a means to regulate body temperature by losing or preserving heat. But there is more.
It has also been suggested that opening their wings allows the flight feathers to recover and regain their shape and function after hours of enduring the demands of flight.
Food and Feeding
All species of vultures are largely scavengers. This means that they feed on dead animals.
Generally, vultures do not kill the animals they eat. However, Black Vultures are known to kill small animals; particularly those that are wounded, about to die, and defenseless. These include sick or wounded animals, hatching turtles, and chicks of ground-nesting birds.
Black vultures are accused of killing newborn calves and lambs. This is partly true. Vultures congregate near cattle or other livestock to eat the afterbirth and end up killing newborns.
A flock of hungry vultures confuse the fresh umbilical cord of a newborn calf and pull on it, causing damage and the eventual calf’s death. The intent, however, was not to kill the newborn but eating the afterbirth that results in the newborn’s death.
The Andean Condor has a similar reputation and is known to perform a similar behavior. The Andean Condor is even accused of driving livestock onto cliffs to kill them and later consume it after they are dead.
There is no evidence of such claim.
The group of Cathartic Vultures (Greater and Lesser Yellow-headed Vultures and Turkey Vulture) have an amazing sense of smell and can find their own food even in dense woodlands.
The Cathartid Vultures are the least aggressive and are not known to attack defenseless animals. Cathartid Vultures have been seen next to dying animals, but they are just waiting for the animal to die without actively killing the animal.
Carcass Preference
The Andean and California Condors and King Vulture search for large carcasses but will consume small carcasses when these are available.
The Black Vulture will consume any small or large dead animal. They will also consume spoiled food, discarded meat, guts, and any other scrap of all sizes. The Black Vulture is the only vulture closely associated with humans and will forage for food right at places where food is being discarded.
The Cathartid vultures are great at finding carcasses of all sizes. They are nearly always the first to arrive at a carcass. When the carcass is small, they will proceed to eat it. When the carcass is large, they need to wait for a king vulture or a condor to tear holes in the carcass and then wait for their turn to eat.
The diet of the Lesser Yellow-headed Vulture is largely composed of large invertebrates, small mammals, snails, dead fish, and small snakes. Birds fly low over grasslands, marshes, and other similar open habitats, smelling for the presence of their prey.
The Lesser Yellow-headed Vulture will congregate at large carcasses found in the habitat types they favor. It has also been observed following tractors for insects flushed, exposed, or killed during agricultural activities.
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Are Vultures Affected by Eating Decayed Meat?
Vultures eat decaying meat. In fact, meat has to be in some state of decomposition for vultures to use their sense of smell and find it.
Decaying meat has a high content of bacterial toxins. Vultures have adapted to detoxify bacterial toxins using strong and neutralizing stomach acids.
Unlike other birds, vultures are immune to botulism, which is food poisoning by a high content of harmful bacteria.
Finding Food
Only the Cathartid vultures, Turkey, and Greater and Lesser Yellow-headed vultures have a superb sense of smell. These vultures are able to smell out carcasses lying on the floor of the dense Amazonian forest.
The Cathartid vultures find virtually every animal that dies in the forest. Even tiny mice carcasses buried in the leaf litter of the forest floor are readily found by these vultures.
Cathartid vultures are very successful birds and occur in large numbers in the ecosystems they live in.
The Cathartid vultures are almost always the first to arrive at a carcass. If it is a large carcass, they rely on large vultures such as the Andean Condor or King Vulture to “break the carcass open.”
The Cathartid vultures are displaced by the larger vultures and the more numerous and aggressive black vultures. They will remain on the sidelines and return to the carcass after other vultures have finished eating.
Vulture Hierarchy at a Carcass
All seven species of vulture, large and small, congregate around large carcasses. Access to the carcass is dictated by the size of each species; larger vultures eat first.
Black Vultures are often the most numerous and most aggressive species on a carcass. They have been known to act collectively to chase away vultures of larger sizes than them.
The smaller cathartid vultures are unable to access the meat and other content. It is the large vultures, with powerful beaks, like that of a condor, that are able to open the carcass. Without the assistance of larger vultures, smaller vultures can only access the carcass through the animals’ orifices or have to wait until the carcass begins to decay further and becomes softer and penetrable.
Upon finding a carcass, vultures remain in the area for several days. Many aggressive interactions occur around the carcass, most of which involve Black Vultures.
Depending on the region, the larger condors and king vultures will take the first turn to eat their favorite parts. Then come the more aggressive black vultures that tear muscles and guts and will gulp large chunks of meat. The Cathartid vultures, Turkey, Greater Yellow-headed, and Lesser Yellow-headed Vultures are usually the last to access the carcass.
The Turkey and Greater and Lesser Yellow-headed vultures eat slowly and carefully get the meat attached to the bones in places other vultures overlook or are unable to reach.
The Lesser Yellow-headed Vulture joins other vultures at large carcasses in grasslands and open habitats they normally occur.
Nesting
Where do Vultures Nest?
In spite of being fairly common and easy to spot, very little is known about the reproductive biology of the Cathartid vultures. Basically, they are secretive nesters.
There is only a few known nests of Turkey Vultures, one nest known of the Lesser Yellow-headed Vulture and none of the Greater Yellow-headed Vulture.
Based on the few known nests, the Cathartid vultures are solitary nesters. They do not build a nest but place two eggs on a small depression at tree stumps, small caves, on the ground under thick bushes, or under the tangled vines that cover the piles of thicket formed by fallen trees. They also nest in large cavities in trees at various heights above the ground.
There are only a handful of known nests of a King Vulture. As with the Cathartid vultures, they nest under stumps, under dense thickets, and in natural cavities in trees. They lay a single egg whitish or creamy white in color. Both parents take turns incubating the egg and will attend to the chick.
The Andean and California Condors choose small caves, ledgers, or shelves in inaccessible cliffs. They lay a single white egg, which is incubated by the two parents.
The American Black Vulture is more generalist. They nest under thick vegetation, piles of logs, structures, and also inside abandoned buildings. Black vultures do not build a nest and lay 2 white eggs.
Nest Defense
Due to the inaccessible nature of the nest site of Andean and California Condors, they appear to be under little pressure from depredation. However, field observations of nests of California Condors reveal that other birds, such as ravens, were a significant source of egg depredation.
The Chathartid vultures and the American Black vulture lay eggs on the ground, and ground-nesting birds are generally thought of as being under high predation pressure.
A mechanism to repel predator attacks is spitting a foul smelly liquid at intruders. Also, their nests are kept terribly smelly, which is thought to discourage potential predators from even approaching the nest. Predators may be discouraged from trying to prey on a chick that is likely to have an awful taste.
How are the young Fed?
The chicks are fed by both parents. During the first few days after hatching, the chicks are fed a predigested liquid. As the chicks grow, the parents feed the young with less and less pre-digested food to a point when the parent brings raw food.
Very young chicks are fed multiple times a day. As they grow older, the frequency of feeding visits decreases to a point where the parents show up at the nest only once a day for only a few minutes.
At What Age do Vultures Start to Breed?
Little is known about the breeding biology of vultures in the wild. From captive animals, the Andean and California Condors attain sexual maturity and begin to breed at the age of six years. This appears to be consistent in the field as the Andean Condor appears to obtain their full adult plumage at the age of six years.
The king Vulture attains the age of sexual maturity and acquires its full adult plumage at the age of four years.
The Cathartic vultures and Black Vulture attain the age of sexual maturity at the age of 3 years.
Photo: Indridgotyoutube/Flickr/CC by 2.0
People and Vultures
Vultures are generally associated with dead animals and garbage dumpsters. Their reputation is not the best. However, they are considered useful birds that rid the environment of dead animals that otherwise would smell for weeks and possibly spread diseases.
Contentious interaction exists mostly with Black Vultures. In some places, Black Vultures bite and peel off rubber frames around windshield wipers of cars.
Black Vultures roost in large flocks, often in residential areas. Their droppings are smelly and considered repugnant by some. Also, the strong acids in vulture droppings kill the trees they roost in and cause damage to the paint of vehicles. Residents in areas near a vultures’ roost want them out for aesthetic and sanitary reasons.
The Andean Condor and Black Vulture have a bad reputation for attacking and killing livestock. Condors, and Black Vultures, are incapable of intentionally killing and carrying live animals. Their feet are incapable of grabbing and carrying anything.
The killing of livestock happens unintentionally. Vultures congregate around livestock giving birth to consume afterbirths. In the feeding frenzy, the birds see the fresh umbilical cord of a calf as a piece of afterbirth and pull on it.
This, unintentionally, kills the calf. Once the calf is dead, the vultures proceed to eat it, hence the reputation.
Vultures in the Ancient Cultures of the Americas
The Cathartid and Black Vultures are little represented in the cultural expressions of native cultures of the Americas.
Ancient cultures associated vultures with death. Their presence circling the sky was often thought of as a bad omen by some; it was an indication that some animal or person may be dying soon.
Condors and King vultures are represented in the cultural expressions of people interacting with them.
The King Vulture is portrayed and referred to in pottery and weaving by the Mayas and Aztec people of Central America and Mexico. Mayas and Aztecs flourished in forested environments where King Vultures occurred.
The California Condor was revered in certain forms by the Native Americans in North America. Parts of California Condors, such as bones and feathers, have been found in burial sites indicating that there was some association between the birds and the dead.
The Andean Condor was widely revered by pre-Inca and Inca cultures. This is evidenced by the presence of this bird in many cultural expressions.
The Andean Condor is carved on the walls of sacred buildings. It was also illustrated on pottery artifacts and weaved in mantles and other ceremonial clothing.
The Andean Condor is represented in the shield of arms and is the national bird of Ecuador, Colombia, Bolivia, and Chile.
Photo: Servicio de Noticias Argentinas.
Threats to Vultures
Vultures are scavengers and also feed on human garbage. They often eat dead animals that have been poisoned to kill other animals. They are not welcome on the thought that they help spread diseases through their droppings as birds move from place to place eating contaminated human garbage.
Vulture species face different threats.
Black Vultures:
- They are blamed for killing newborn calves and lambs. They gather around livestock giving birth to eat the placenta and other afterbirths. In the feeding frenzy, vultures see the fresh umbilical cord as an afterbirth and pull on it, causing the eventual death of the newborn.
- They are accused of spreading salmonella and being a vector for other illnesses. Black Vultures feed on human garbage flying from place to place spreading pathogens through their droppings.
- They are accused of killing the trees they roost in and creating unsanitary conditions by depositing droppings underneath their roosts.
King Vulture and Greater Yellow-headed Vultures
The main threats for these two forest vultures include:
- Loss of habitat. As deforestation advances, these vultures lose habitat.
- Loss of their food base. As the Amazon Rainforest is settled, modern and more efficient firearms are used by humans for hunting wildlife. This results in forests depleted of Amazonian wildlife. Over time, animals that would have normally died and served as vulture food are no longer there.
Andean Condor
- The main threat for the Andean Condor is killing by shooting and poisoning. The Andean Condor is accused of killing young calves and lambs. Often times condors are killed when they consume poisoned bait directed to them or other livestock predators such as foxes and pumas.
California Condor
The California Condor has a long history of decline. From being a widespread species in all of North America, it became restricted to the Pacific mountain range in the western United States.
Students of the condor speculate that such reduction of range resulted from the massive extinction and loss of its large mammal prey base that occurred after the Pleistocene glaciation some 11,000 years ago.
After the natural reduction of the species range, the condor population continued to decline. Shooting, egg collecting, and poisoning might have been the reasons for the continued decline. During that time, wolves and coyotes were a problem for livestock and were eliminated by baiting carcasses with poison. Many condors also ate the bait and died.
Another probable cause of condor mortality was lead poisoning. Deer, ducks, and other game that are shot but manage to run and die later are consumed by condors, which consume the ammunition lodged in these animals and die.
References:
- Buechley, Evan R.; Sekercioglu, Cagan H. (2016). “Vultures.” Current Biology. 26 (13): R560–R561.
- Conger, Cristen (2008-10-13). “Why is it a bad idea to scare a vulture?”. HowStuffWorks.
- Vultures: All About Birds, Cornell Lab of Ornithology.
- Vultures: Handbook of the Birds of the World.
- Ward, J.; McCafferty, D.J.; Houston, D.C.; Ruxton, G.D. (April 2008). “Why do vultures have bald heads? The role of postural adjustment and bare skin areas in thermoregulation”. Journal of Thermal Biology. 33 (3): 168–173.