Lesser Yellow-headed Vulture, Cathartes burrovianus
The Lesser Yellow-headed Vulture (Cathartes burrovianus), also known as the Savannah Vulture, is a species of bird belonging to the New World Vulture family Cathartidae. It was considered to be the same species as the Greater Yellow-headed Vulture until they were separated in 1964. It can be found in Mexico, Central America, and South America in seasonally wet or flooded lowland grassland, heavily degraded former forests and swamps. It’s a large bird, with a wingspan of 59 to 65 inches. The body plumage is black, and the neck and head, which are featherless, are a pale orange color with red or blue areas. It lacks a syrinx, therefore, its vocalizations are limited to grunts or low hisses.
This bird feeds on carrion and locates carcasses by smell and sight, an ability which is rare in birds. Its dependent on larger vultures, such as the King Vulture, to open the hides of larger animal carcasses as its bill isn’t strong enough to do so. Like other New World Vultures, the Lesser Yellow-headed Vulture uses thermals to stay aloft with minimal efforts. It lays its eggs on flat surfaces, such as cave floors, or in the hollows of stumps. It feeds its young by way of regurgitation.
It was initially described in 1845 by John Cassin, sometimes recognized as having two subspecies. The first, Cathartes burrovianus urubitinga, described by Australian ornithologist August von Pelzeln in the year 1851, is the larger of the two and can be found from Argentina north to Columbia, while the nominate species, Cathartes burrovianus burrovianus, is smaller and can be found from northwestern South America through Central America to Mexico.
The exact taxonomic placement of this bird and the remaining six species of New World Vultures remains unclear. Although both are similar in their appearance and have similar ecological roles, the New World and Old World Vultures evolved from different ancestors in different parts of the world. Just how different the two are is currently under debate, with some earlier authorities suggesting that New World Vultures are more closely related to the storks. More recent authorities keep up their overall position in the order Falconiformes along with the Old World Vultures or place them in their own order, Cathartiformes. The South American Classification Committee has removed the New World Vultures from Ciconiiformes and instead placed them in Incertae sedis, but notes that a movement to Falconiformes or Cathartiformes is possible. Like other New World Vultures, the Lesser Yellow-headed Vulture contains a diploid chromosome number of 80.
This bird is 21 to 26 inches in length, with a wingspan of 59 to 65 inches and a tail length of 7.5 to 9.4 inches. Its weight ranges from 2.1 to 3.4 pounds. The plumage is black with a green gleam. The throat and sides of the head contain no feathers. The neck and head are bare of feathers as well, and the skin is yellow, with a reddish colored forehead and nape and a grayish blue crown. The irises of the eyes are red, its legs are white, and its beak is the color of flesh. The eye has a single incomplete row of eyelashes on the upper lid and two rows of eyelashes on the lower lid. The tail is rounded and comparatively short, for a vulture; the tip of the closed wing stretches beyond the tail. Immature Lesser Yellow-headed Vultures have a browner plumage, a dusky head, and a white nape.
The beak is rounded, thick, and hooked at the tip. The front toes are long with small webs at the bases and are not adapted to grasping. The opening of the nostril is longitudinal, and the nostrils do not have a septum. Like all New World Vultures, this bird lacks a syrinx, and is therefore unable to make any noise other than a low hiss.
The appearance differs in several ways from the Greater Yellow-headed Vulture. It is smaller than the Greater Vulture and has a shorter and thinner tail. The plumage color is browner than the Greater Vulture’s dark glossy black plumage. Its legs are lighter in color, and its head is more orange-tinted than the more yellow colored head of the Greater Yellow-headed Vulture. Its flight is also less steady than that of the Greater Vulture. The Lesser Vulture also prefers to reside in savannas, as opposed to the preferred forest habitat of the Greater Vulture, and is less heavily built.
Besides the Greater Yellow-headed Vulture, it is much like the Turkey Vulture.
It can be found in Belize, Bolivia, Argentina, Columbia, Chile, Brazil, Ecuador, El Salvador, Costa Rica, Guatemala, Guyana, French Guiana, Honduras, Mexico, Panama, Nicaragua, Peru, Suriname, Paraguay, Uruguay, and Venezuela. Its natural habitats are tropical and subtropical seasonally wet or flooded lowland grassland, mangroves, swamps, and heavily degraded former forest. It might wander over fields and clearings. It’s not usually found in high-altitude regions.
It flies solitary, with its wings held in a dihedral position. It glides at a low altitude over wetlands while searching for food, and perches on fence posts or other low perches. When flying, it travels alone and is rarely ever found in groups. The flight of the Lesser Yellow-headed Vulture is an example of a static soaring flight, which uses thermals to keep a steady altitude without the need to flap its wings. This vulture rarely ever soars high in the air, preferring low altitudes. This bird is believed to be somewhat migratory in response to the changes in water level around its home. The Lesser Yellow-headed Vulture, like the other New World Vultures, has the strange habit of urohidrosis, in which it urinates or defecates on its legs to cool them by evaporation.
It is a scavenger and subsists almost entirely on carrion. It will eat road kill or the carcass of any animal, but is also known to hunt for its food, particularly small aquatic animals in marshes. It prefers fresh meat, but often cannot make the first cut into the carcass of a larger animal due to its beak not being strong enough to tear into the tough hide. It will no longer feed on a piece of carrion one the meat is in a state of extreme decay, as it becomes contaminated with microbial toxins. Like other vultures, it plays a significant role in its ecosystem by disposing of carrion which would otherwise be a breeding ground for diseases.
This bird forages using its keen eyesight to locate carrion on the ground, but also uses it sense of smell, an ability which is uncommon in the avian world. It locates the carrion by detecting the scent of ethyl mercaptan, which is a gas produced by the beginnings of decay in dead animals. The olfactory lobe of its brain that is responsible for processing smells is particularly large compared to other animals. This trait of New World Vultures has been used by humans: ethyl mercaptan is injected into pipelines, and engineers looking for leaks then following the foraging birds.
King Vultures, which aren’t able to smell carrion, follow the Lesser Yellow-headed Vultures to carcasses, where the King Vulture tears open the skin of the dead animal. This enables the Lesser Yellow-headed Vulture access to food, as it does not have a bill strong enough to tear the hide of larger animals. This is an example of mutual dependence between species. It’s generally displaced from carcasses by both Turkey Vultures and King Vultures, because of their larger size.
They do not build nests, but rather lay their eggs on the ground, cliff ledges, cave floors, or in the hollow of a tree. The eggs are cream colored and heavily blotched with brown and grey spots, particularly around the larger end. Two eggs are usually laid. The chicks are altricial – they are blind, naked and comparatively immobile upon hatching. The chicks do not grow their down feathers until much later. The parents feed their young by regurgitating pre-digested food into their beak, where the chicks then drink it. Young fledge after two or three months.
It is a bird of Least Concern according to the IUCN, with an estimated global range of 7,800,000 sq km and a population of between 100,000 and 1,000,000 individual birds. The population trend seems to be stable.
Image Caption: Lesser Yellow-headed Vulture (Cathartes burrovianus) at Tennoji Zoo in Osaka, Japan. Credit: pelican/Wikipedia (CC BY-SA 2.0)