(c) Anthony K. Grafton 2003

Yellow Face, Bad Breath

What would make a bird want to spend time eating animal dung? That’s what a group of scientists in Spain wanted to know about a rare bird known as the Egyptian vulture. This vulture lives around the Mediterranean sea in southern Europe and northern Africa. Its habit of eating animal dung has been known for years, but no one new why it sought out such an unsavory feast.

Scientists studied the Egyptian vulture and found that it usually consumes dung from grazing animals, and that this waste product had very little nutritional value. However, they found that the dung did contain plenty of carotenoids (ke-rat-ehn-oids), a kind of chemical that can be used as pigments and colors. And the scientists also noted that the Egyptian vulture has a brightly colored, yellow face.

Wondering if the color of the vultures faces was related to the pigments in the dung, the scientists conducted a series of experiments. They tested the chemicals in the skin of the vulture’s faces and found that it matched the chemicals found in the dung. They also found high levels of the chemicals in birds that were fed nothing but cow dung. And finally they noticed that birds that lived near greener fields with more cattle had faces with a brighter yellow color. All the evidence allowed the scientists to conclude that the Egyptian vulture consumes dung to help it maintain a bright yellow face.

What good would it be to have a yellow face? For one thing, the scientists speculate that the bright yellow color could be useful in attracting mates. But this would only be an evolutionary advantage if brighter faces meant a healthier male bird. This would make sense if you consider that birds that eat enough dung to gain a rich color would have been exposed to a lot of parasites in the dung, and therefore must be strong and healthy to survive it. So, female Egyptian vultures may look for yellow faces to pick out a healthy male partner.

Can you think of other animals that use interesting or strange ways to attract mates? Send your answers to Science Corner.