As I said before, only a mother could love the bald head of a vulture. Old World vultures (Nubian, Egyptian, white-backed vultures, among others) and New World vultures (turkey vultures, black vultures and California condors) are not related, however, both groups have heads without feathers. This is an example of convergent evolution – where unrelated species develop similar traits as a response to similar environmental conditions.
What similar environmental cues? Vultures are carrion eaters, as are eagles, ravens, and other raptors, to name a few examples. Why are these other consumers of dead flesh not bald too? The difference is in how the bird eats. Once the skin of a dead animal is broken, a vulture will dig deep into the body cavity and aggressively consume internal organs. Meanwhile other carrion eaters pick the meat from the outside, never exposing or burying their heads in gore. Very simply, a bald head is easier to keep clean and more hygienic than feathers, a very practical reason for a featherless head considering the vulture’s diet and method of eating.
Thor Hanson in his book Feathers devotes a chapter to the bald-headed vultures. He studied vultures in Kenya and describes his experience with putrefied blood and guts sticking to his hair and skin after accidentally breaking open a zebra cecum. That led him to experiment with chicken feathers and frog guts. Indeed, once covered with blood, the chicken feathers were almost impossible to clean. Preening would never remove all the blood and viscera. Although ugly, the bald head of vultures serves a very useful purpose.
This turkey vulture (Cathartes aura) was photographed near our house (Lookout CA). It is interesting how large the nares are and that one can see directly through them. I wonder if that has something to do with their acute sense of smell? Or perhaps the large nares have also evolved in response to the eating style of the bird? Large nares are less likely to clog with viscera is one possible explanation. A new topic to research. . .