Why Are Vultures Bald? The Real Reason Behind Bare Heads

The traditional answer: staying clean

The classic explanation is hygiene. Vultures feed on carcasses, and many species push their heads deep into the body of a dead animal to reach soft tissue. Feathers on the head and neck would get matted with blood and rotting meat, and they would be very hard for the bird to clean, because a bird cannot reach its own head with its bill to preen.

Bare skin, by contrast, dries quickly and can be cleaned by rubbing or simply by exposure to the sun and air. Some people have also suggested that sunlight, with its ultraviolet rays, helps kill bacteria on bare skin, although this has not been firmly tested.

The hygiene idea makes sense, and it may still be part of the story. But it does not explain everything. Some scavengers that feed on carcasses, such as eagles and ravens, have fully feathered heads, and vultures are usually seen with fairly clean heads even after feeding.

The newer answer: controlling body temperature

In 2008, a team of researchers from Scotland published a study of vultures’ heat regulation in the Journal of Thermal Biology. They measured heat loss from the birds’ heads and necks with thermal imaging and watched how the birds held their bodies at different temperatures.

They found that vultures used their bare skin like a radiator. On cold days, the birds hunched down and tucked their bare necks into the feathers of their bodies, or raised a ruff of neck feathers, to reduce heat loss. On hot days, they stretched their necks out, exposing as much bare skin as possible to let heat escape.

This makes sense for birds that live in extreme conditions. Many vultures soar high in cold air, then land in hot, open country to feed in full sun. Being able to switch heat loss on and off by changing posture is an efficient way to cope with both. The researchers concluded that temperature control was probably the main reason for bare heads, with hygiene perhaps a secondary benefit.

New World vs Old World vultures

There are two separate groups of vultures, and both evolved bald heads independently.

New World vultures live in the Americas and form their own family, Cathartidae. It includes the turkey vulture, the black vulture, the king vulture and the two condors. Their heads are bare to the neck, often brightly colored: red in the turkey vulture, gray-black in the black vulture, and orange, red and purple in the king vulture.

Old World vultures live in Europe, Africa and Asia and belong to the same family as hawks and eagles. Griffon vultures, white-backed vultures and lappet-faced vultures have bare or downy heads and long necks, often with a ruff of feathers at the base.

The two groups are not closely related. They look alike because they evolved for the same way of life, a pattern known as convergent evolution. That both groups ended up with bare heads strongly suggests the trait is useful for scavenging birds in hot climates.

Condors and other bald birds

The largest bald-headed birds are the condors. The Andean condor has a bare, dark red to blackish head and neck, and adult males have a large fleshy comb and wattles. The California condor has a bare head that can range from pinkish orange to red, and the color can flush brighter when the bird is excited, which helps condors signal to one another.

So bare skin can also be a signal. In several vulture species, the color of the head changes with age, mood or social status. A young turkey vulture has a gray head that turns red as it matures, a visible sign of adulthood. A similar idea applies to the bare red head and dangling snood of the wild turkey, as described in what is the red thing on a turkey?.

Other birds have bare heads for different reasons. Several storks and ibises have bare heads and necks, including the marabou stork of Africa, which also scavenges at carcasses.

Vultures with feathered heads

Not every vulture is bald. The bearded vulture, also called the lammergeier, of Europe, Africa and Asia has a fully feathered head with a black “beard” of bristles under the bill. It feeds mainly on bones and marrow rather than plunging into soft carcasses, so its feathers stay clean.

The palm-nut vulture of Africa, which eats mostly oil palm fruit, also has feathers on most of its head and only a small patch of bare skin around the eye. These exceptions support the link between baldness and a diet of carcasses.

How bare heads help vultures stay healthy

A bare head is only one of several defenses against the germs that live in rotting meat. Vultures have extremely acidic stomachs that kill many bacteria. A 2014 study of the gut microbes of turkey vultures and black vultures found that the bacteria on the birds’ faces were very diverse, while those in the gut were much less so, suggesting that most germs are destroyed during digestion.

Together, these traits let vultures do a job few other animals can: cleaning up carcasses quickly and safely. That service helps keep disease from spreading in the wild and near people.