The function of the cosmetic coloration of bearded vultures: when art imitates life

Abstract

Origin of Red Plumage in Bearded Vultures Free-ranging adult bearded vultures, Gypaetus barbatus, typically have a rich orange colour on their underparts, neck and head. Wild birds, however, vary considerably in coloration and captive birds have a pure white ventral plumage. Rufous birds are the most usual colour morph throughout the range of the species, except in the small populations of the Mediterranean islands of Corsica (Thiollay 1968) and Crete (Xirouchakis 1998), where white birds are common. The origin of the coloration has been debated since at least the 19th century (Berthold 1967 and references therein). It was once attributed to carotenoid pigments (Clancey 1968), which are responsible for red, yellow and orange colours in other species (Brush 1990). We now know, however, that the orange colour comes from soils stained with iron oxide (Berthold 1967; Brown & Bruton 1991; Houston et al. 1993). Ferruginous colours are not exclusive to bearded vultures: many bird species, mostly waterfowl and cranes (Kennard 1918; Höhn 1955), have traces of iron oxide in their plumage. The bearded vulture, however, is the only avian species known to dye its plumage from soils to such an extent (Houston et al. 1993) and to do so deliberately (Frey & Roth-Callies 1994; see below). Early doubts on the origin of the bearded vulture's coloration (e.g. Clancey 1963) were also based on the lack of observations of bearded vultures bathing in red soils. In a 3-year study, which included the intensive tracking of radiotagged birds with rufous coloration, Brown (1988) often observed individuals bathing in water free of iron oxides, but never saw the birds deliberately rubbing themselves on red soils. Brown (1988) and Brown & Bruton (1991) suggested that staining was acquired passively, with no specific behaviour, when vultures came into contact with iron oxide deposits in places where they perched or at nests. This hypothesis, however, was questioned when captive white birds were provided with damp red soils (Houston et al. 1993; Frey & Roth-Callies 1994). The birds rubbed their bellies and heads in the soil, thus developing the characteristic deep rufous colour of wild birds. The behaviour pattern was different when birds bathed in water or in damp red soils. In the first case, they plunged into the water and then just shook the soaked plumage. However, when bathing in red soil, the bearded vultures rubbed themselves against the substratrum and preened the plumage for up to 1 h. The birds first transferred the damp mud that adhered to the ventral area to the shoulders and upper back with the beak and talons. Then the head was swung repeatedly between the shoulders and back, which soon acquired the orange colour. Nothing is known about bathing frequency in the wild, but captive birds offered new red soil every 2 weeks tended to use it immediately (A. Llopis, personal communication). Still another argument against the passive acquisition of the ferruginous colour is that large, white birds of prey that often perch and breed in the ...

How Birds Combat Ectoparasites

“…For example, Bearded Vultures (Gypaetus barbatus) stain their plumage with soils that are rich in iron oxide Fig. (12), [203,204]. They either rub their plumage in dry red soil, or rub damp red soil into their plumage following a bath.…”

“…They either rub their plumage in dry red soil, or rub damp red soil into their plumage following a bath. Vultures spend as much as an hour applying the soil [204]. Captive Bearded Vultures return to their nests following episodes of soil bathing and rub their newly stained feathers on eggs and offspring [205].…”

“…Captive Bearded Vultures return to their nests following episodes of soil bathing and rub their newly stained feathers on eggs and offspring [205]. Frey and Roth-Callies [203] [cited in Negro et al [204]] tested for an effect of iron oxide on lice, but there was no significant difference in the survival of lice exposed to a suspension containing iron oxide vs. water controls. Arlettaz et al [205] argued that, since Bearded Vultures are often the last species to feed upon carcasses, they may also be exposed to dangerous quantities of bacteria left behind by earlier scavengers.…”

The influence of an interactive educational approach on visitors' learning in a Swiss zoo

“…Although some bird species have traces of iron oxide in their plumage, the bearded vulture is the only avian species known to dye its plumage from soils extensively and deliberately (Negro et al, 1999). Visitors were invited to color feathers with red soil at the touch table.…”

The evolutionary ecology of decorating behaviour

“…Colour tends to be greater in (socially dominant) females than males and increases progressively from juveniles, to immatures, to sub-adults to adults. This caused Negro et al [34] to interpret the red coloration as a status signal. They argue that sites where such soils are available will be rare, with substantial costs associated with finding them and gaining access to them in intraspecific contests.…”