The Bearded Vulture (Gypaetus barbatus) is known for its innate tendency to bathe in ferruginous water springs up in the mountains, from which they get a rufous colour on their chest and face. This fascinating “cosmetic behaviour” has triggered the curiosity of many researchers over the last decades, and although different hypotheses have been proposed, none has yet proven conclusive. A recently published scientific study provides new insights into this secretive behaviour and reinforces the importance of safeguarding these iron-rich puddles.
The Cosmetic Behaviour of Bearded Vultures
Bearded Vultures often bathe in ferruginous water springs containing high levels of iron oxides to deliberately taint their whiteish chest and facial feathers to a dark orange-brown colour. It seems an innate condition; if a bowl for mud baths is provided in captivity, 90-day-old nestlings can be seen bathing in the mud when undisturbed. These observations also signal their good health status.
Curiously, another study sheds light on how the Homo neanderthalensis and Homo sapiens, which have also stained their bodies more than 100 000 years, could have possibly mimicked the observed behaviour from Bearded Vultures – and benefited from the multiple anti-UV anti-bacterial benefits these muds confer.
Why do they bathe? Hypothesis describing the cosmetic behaviour of Bearded Vultures
Several hypotheses to describe the function of this cosmetic behaviour have been proposed, the most accepted being a means of showing individual dominance. According to the authors, in captive settings, the degree of ochre colouration is linked to the age and sex of Bearded Vultures: older individuals and females (the dominant sex) are more pigmented. In the wild, females also display more intense pigmentation, and in the case of polyandrous trios, alpha males typically manifest stronger colours than beta males.
Other hypotheses were also considered based on iron oxides’ potential anti-bacterial and anti-parasitic benefits and their possible feather-protection capability. However, a study has demonstrated that the iron-rich mud could not prevent feather degradation and the inexistence of antibacterial effects in some iron particles and minerals. The most recent hypothesis focuses on the attenuating effects of these mud baths, suggesting that birds with “feather imperfections may benefit from concealing them with ochre”. The hypothesis remained untested until recently.
Bearded Vulture bathing in mud in cañón de Añisclo in Parque Nacional de Ordesa and Monte Perdido, Pyrenees © Javier Barrio 2019
Recent insights into Bearded Vulture Cosmetic Behaviour
To understand the mysterious intentions behind this behaviour, researchers have monitored the use of a ferruginous spring in the Catalonian Pyrenees with the help of camera traps between October 2021 and February 2023 and GPS devices (of tagged individuals). At least 24 individuals from different age classes were identified based on their plumage characteristics (age classes were divided accordingly: juveniles, up to 2 years old; immatures, three; sub-adults, five-six; and adults, over six years old).
Four juveniles, three immatures, six sub-adults and ten adults visited the monitored spring, mainly in the middle of the day (from 9h to 16h). Of the 24, only 15 bathed; others drank water and snow or perched on the ground for a few minutes. According to the authors, 80,9% only visited the site once. There is, however, a record of a sub-adult that visited the spring seven times in the same year.
Key findings reinforce:
- Their secretive behaviour: Most of the visits (93,4%) were done isolatedly by individuals, and bathing behaviour only occurred when they were alone. After all, everyone likes privacy!
- The variability of individuals with tainted feathers in opposition to white or pale individuals might be explained by the absence of an iron-rich water puddle;
- 50% of the visits were done by non-adults, “which have brown plumage against which human observers do not see the orange colouration”.
The authors suggest that
“Cosmetic colouration function as an attenuating signal (the opposite of an amplifier) that could benefit low-quality and subordinate individuals.”A. Margalida et al. (2023)
While further research is recommended, the article emphasises the importance of these ferruginous water springs for Bearded Vulture populations. Authors call on policy-makers and conservationists for proper identification of these sites and regulatory and protection guidelines to recognise them as priority areas for Bearded Vulture conservation.
Source: Margalida, A.; Almirall, I.; Negro, J.J. New Insights into the Cosmetic Behaviour of Bearded Vultures: Ferruginous Springs Are Shared Sequentially. Animals 2023, 13, 2409. https://doi.org/10.3390/ani13152409