The Lesser Yellow-headed Vulture, Cathartes burrovianus, also known as the Savannah Vulture, is a species of bird in the New World Vulture family Cathartidae. It was considered to be the same species as the Greater Yellow-headed Vulture until they were split in 1964. It is found in Mexico, Central America, and South America in seasonally wet or flooded lowland grassland, swamps, and heavily degraded former forest. It is a large bird, with a wingspan of 150-165 centimeters (59-65 in). The body plumage is black, and the head and neck, which are featherless, are pale orange with red or blue areas. It lacks a syrinx, so therefore its vocalizations are limited to grunts or low hisses.
The Lesser Yellow-headed Vulture feeds on carrion and locates carcasses by sight and by smell, an ability which is rare in birds. It is dependent on larger vultures, such as the King Vulture, to open the hides of larger animal carcasses as its bill is not strong enough to do this. Like other New World Vultures, the Lesser Yellow-headed Vulture utilizes thermals to stay aloft with minimal effort. It lays its eggs on flat surfaces, such as the floors of caves, or in the hollows of stumps. It feeds its young by regurgitation.
The exact taxonomic placement of the Lesser Yellow-headed Vulture and the remaining six species of New World Vultures remains unclear. Though both are similar in 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 the New World vultures are more closely related to storks. More recent authorities maintain 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 move to Falconiformes or Cathartiformes is possible.
The Lesser Yellow-headed Vulture is 53-65 centimeters (21-25.5 in) in length, with a wingspan of 150-165 centimeters (59-65 in) and a tail length of 19-24 centimeters (7.5-9.5 in). Its plumage is black with a green sheen. The throat and the sides of the head are featherless. The head and neck are bare of feathers, and the skin is yellow, with a reddish forehead and nape and a gray-blue crown. The irises of its eyes are red, its legs are white, and its beak is flesh-colored. The eye has a single incomplete row of eyelashes on the upper lid and two rows on the lower lid. The tail is rounded and relatively short for a vulture; the tip of the closed wing extends beyond the tail. Immature Lesser Yellow-headed Vultures have browner plumage, a dusky head, and a white nape.
The beak is thick, rounded, and hooked at the tip. The front toes are long with small webs at their bases and are not adapted to grasping. The opening of the nostril is longitudinal, and the nostrils lack a septum. Like all New World Vultures, the Lesser Yellow-headed Vulture lacks a syrinx, and is therefore unable to make any sound other than a low hiss.
It differs in appearance from the similar Greater Yellow-headed Vulture in several ways. It is smaller than the Greater Yellow-headed Vulture and has a shorter, thinner tail. The plumage is browner than the Greater Yellow-headed Vulture's dark, glossy black plumage. Its legs are lighter in color and its head is more orange and less yellow than that of the Greater Yellow-headed Vulture. Its flight is also less steady than that of the Greater Yellow-headed Vulture. The Lesser Yellow-headed Vulture also prefers to live in savannas instead of the Greater Yellow-headed Vulture's forests and it is less heavily built.
It is found in Argentina, Belize, Bolivia, Brazil, Chile, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, Uruguay, and Venezuela. Its natural habitats are subtropical or tropical seasonally wet or flooded lowland grassland, swamps, mangroves, and heavily degraded former forest. It may wander over dry fields and clearings. It is not generally found in high-altitude regions.
The Lesser Yellow-headed Vulture forages using its keen eyesight to locate carrion on the ground, but also uses its sense of smell, an ability which is uncommon in the avian world. It locates carrion by detecting the scent of ethyl mercaptan, a gas produced by the beginnings of decay in dead animals. The olfactory lobe of its brain responsible for processing smells is particularly large compared to other animals. This characteristic of New World Vultures has been used by humans: ethyl mercaptan is injected into pipelines, and engineers looking for leaks then follow the foraging vultures.
King Vultures, which lack the ability to smell carrion, follow the Lesser Yellow-headed Vultures to carcasses, where the King Vulture tears open the skin of the dead animal. This allows the smaller 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 is generally displaced from carcasses by both Turkey Vultures and King Vultures, due to their larger size.