Rotbadstelle
As Rotbadestelle is called the bodies bearded vulture and the Egyptian vulture traditionally use to their feathers with containing iron oxide sludge to color. This behavior was unknown for a long time. It was only noticed that bearded vultures kept in captivity have white plumage on the underside. However, adult birds observed in the wild are reddish brown on the underside of their bodies.
Checks then showed that bearded vultures sought out places with mud containing iron oxide and smeared themselves there with the red mud. After it was already observed in captured birds that they used water containing iron oxide to color their plumage, this behavior in the very rare birds was only observed in the field in May 1995. In 2002, the behavior of Egyptian vultures was also proven. Egyptian vultures, however, prefer more yellowish tones than bearded vultures.
The background to this innate behavior is still unknown. An improvement in thermoregulation , wear protection for the plumage and visual signal effects in social behavior are discussed as explanatory approaches.