One of the most fascinating – and mysterious, features of the animal worlds relates to the preference of bearded vultures to bath in iron-rich mud to acquire the well-known and spectacular orange colour of their plumage.
Researchers have yet to establish a clear correlation with biological parameters - there is still controversy about whether feather painting plays a role in visual communication or primarily functions as protection against bacteria or viruses but it looks now that Egyptian vultures also do this deliberate staining of feathers, from a recent paper published in Ecology (see below).
The evidence comes from a study in the Canary Islands, where about 85% of the 300 or so Egyptian vultures living on Fuerteventura (Canary Islands, Spain) are colour ringed and regularly monitored at supplementary feeding sites.
During monitoring This van Overveld et all noticed that there was some remarkable individual variation in the amount of rufous coloration on parts of the neck and head, with some birds with an almost entirely red plumage. The authors then presented two bowls to the vultures, one with red soil dissolved in water and one containing only water. More than 20% of the birds visiting the feeding station then dyed their heads, neck and chest feathers with the red soil, while only one bird took a bath in the bowl with clear water. Mud bathing was done by both males and females, immature birds and even recently fledged young.
However, not all birds died their heads - whereas some birds were highly attracted to the mud, others showed very little interest, and there was also a wide variety ion the extent birds dyed their feathers.
You can see some videos of the species mud bathing at the links below.
van Overveld, T. 2017a. Egyptian vulture mud bathing I.
van Overveld, T. 2017b. Egyptian vulture mud bathing II.
van Overveld, T. 2017c. Egyptian vulture mud bathing III.
Photo: Bruno Berthémy/VCF