And you thought Botox was weird. The Egyptian vulture has an even more remarkable way to beautify its face: eating feces. A study in the 25 April issue of Nature suggests this seemingly repulsive habit may be designed to help vultures attract mates or warn off rivals.
One of the main explanations for animal ornamentation is that it communicates social dominance or suitability as a mate. Pigmentation, for example, is costly to produce, so it implies that a bird has a wealth of energy reserves and is free of parasites--good qualities in a mate and good intimidation for competitors. Biologist Juan Negro and colleagues at the Doñana Biological Station in Seville, Spain, thought the Egyptian vulture was a good test case for this theory. The bird, a scavenger found in Southern Europe and parts of Africa and India, has a bright yellow face and eats the excrement of cows, sheep, and goats. The researchers hypothesized that a bright face signals that a bird is vigorous and virile--able to eat lots of dung and still fend off an army of parasites.
To investigate how vultures might benefit from their doo-doo diet, the researchers analyzed the nutrients in domestic manure and found very little in the way of protein or fat. What they did find was lutein, the same carotenoid pigment that's abundant in vulture skin. Zoo vultures fed only meat, their usual food, had very low blood lutein levels and pale faces. But when these vultures were treated to steaming heaps of cow dung, their lutein levels rose markedly, presumably giving them the raw ingredients to freshen up their faces.
This is "a unique finding among vertebrates," says Gary Bortolotti, an ornithologist at the University of Saskatoon in Canada, adding that it's "a wonderful contribution to our understanding of both carotenoids and coloration in birds." As for scat-scarfing as a sexual signal, he says it's "very plausible." Negro says a study is under way on the relationship between facial color and mating success, which should determine whether the theory is more than just a pile of manure.
The Doñana Biological Station