Beauty secrets of dung-eating bird

Egyptian vulture: Only species with a yellow face

Feeding on cowpats is not known for aiding the complexion.

But it seems that for the rare Egyptian vulture, this is an essential part of the daily beauty regime.

Biologists have found that the bird pecks at droppings to keep its face bright yellow.

The yellow face works as a visual signal - brighter individuals would be preferred as mates

Juan Negro and colleagues

The filthy habit may even impress a mate.

Spanish scientists say the bird's brilliant complexion probably signals to a suitor that it is healthy and strong.

The Egyptian vulture has earned the nickname "churretero" and "moniguero" in Spain, meaning dung-eater.

The birds can often be seen pecking at cow, sheep and goat droppings.

The reason for the strange diet has been a mystery until now.

It seems that the dung of hoofed animals contains pigments the birds cannot make in their own bodies.

Carrot pigment

These substances - carotenoids - are what give roots such as carrots their orange colour.

All animals need them as part of a healthy diet. But Egyptian vultures consume them in excess to keep their faces bright.

They cannot get them from their customary food - rotten flesh and bones - so they eat dung.

The habit presumably evolved to give the message to potential mates that the bird was strong enough to fight off any infection they might catch from the cow dung.

It could also signal that the bird is at the top of the pecking order.

Visual signal

Dr Juan Negro and colleagues of Estacion Biologica de Donana, Seville, believe this is the first known case of a back-boned animal using dung as a source of carotenoids.

Dr Negro told BBC News Online: "We believe the yellow face works as a visual signal.

"Brighter individuals would be preferred as mates and may also be dominant over paler individuals."

This is the theory for all bird species with carotenoid-dependent colouration, he said. But it has been demonstrated in very few species and only with captive birds.

The vulture's eating habits are revealed in the scientific journal Nature.

Image courtesy of Dr Juan Negro, Estacion Biologica de Donana, Seville.