Vultures smear their faces in red mud which they use as makeup
A species of vulture has been filmed putting on make-up for the first time – a rare phenomenon in birds, known as cosmetic colouration. The Egyptian vulture normally has a yellow wrinkled face surrounded by a halo of white hair. But on Fuerteventura island in the Canaries off the coast of Africa, many vultures sport reddish heads and necks, with the colour varying from pale brown to deep crimson. These vultures dip their heads in red soil and swipe from side to side, carefully dyeing their head, neck and chest red. It is a well-studied population, so almost every vulture on the island is marked with plastic rings, allowing researchers to study individual differences in this curious behaviour.
“It’s the first documentation of this behaviour in wild birds that are individually marked,” says Thijs Van Overveld of Doñana Biological Station in Spain. To see it up-close, Overveld and his colleagues kept two bowls in the island’s feeding station, one filled with red soil dissolved in water, the other with just water. As the hidden researchers watched, the vultures took their mud baths.
The birds examined the muddy water, scratched about with their legs, and then gently swiped both sides of their heads in the mud, emerging with red head, neck and chest feathers. Out of about 90 birds that visited over one day, 18 took mud baths. A couple of vain individuals even had two baths.
“The most interesting part of our observation is that there is great variation among individuals in the extent to which they paint feathers, ranging from almost completely white to almost completely red,” says Overveld. The vultures did not follow a particular pattern while mud painting and the baths were not restricted to a particular age, or sex.
Although the related bearded vulture is known to display a similar behaviour as a signal of dominance, the researchers don’t believe that Egyptian vultures paint themselves for this reason. Unlike the Egyptian vultures in the Canaries, the bearded vulture goes for its mud baths in secret, and the mud daubing itself is a lot more elaborate. Also, the bearded vulture is solitary, and the authors say signalling dominance may be more important for them.
So why do the Egyptian vultures do it? One possible explanation is that the mud keeps bacteria and viruses away. But, if bathing had such a big advantage, many more birds should be taking long mud baths. The authors believe instead that the painting serves a visual rather than health-related purpose, “given the great effect on the general appearance of these otherwise white birds.”
Robert Montgomerie from Queen’s University in Ontario, Canada, thinks so too. “The amount and incidence of reddish head plumage on Egyptian vultures is quite rare, suggesting that those who have it are indicating something special,” he says. But it remains to be seen what that function might be.
Some other birds are known to apply “cosmetics” to change the way they look. Many, including flamingos, secrete waxy substances that they apply on feathers while preening to give them a glossy sheen. Birds using dyes from their environment to change the way they look is rarer. Examples include sandhill cranes that apply soil on themselves as camouflage when nesting, and close to the Arctic, when snow melts, perfectly camouflaged snowy white ptarmigans become suddenly conspicuous, and start applying mud as camouflage.
15 May 2017
Journal reference: Thijs van Overveld, Manuel de la Riva, Jose Antonia Donazar (2017) Cosmetic coloration in Egyptian vultures: Mud bathing as a tool for social communication? Ecology: May 2017; DOI: 10.1002/ecy.1840
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