Ferruginous springs as colouring sites for Bearded Vulture (Gypaetus barbatus): characterisation, availability and applications for species conservation in the French Pyrenees

Bearded Vultures deliberately stain their feathers with iron oxides from ferruginous springs (FS) to acquire orange colouration. This uncommon behaviour is believed to play an important role in the relationship between individuals, so FS may constitute a strategic resource for the species. In the French Central-Western Pyrenees, we surveyed and mapped FS, checked those used by Bearded Vultures and characterised their habitat variables and geological features. We also evaluated FS availability in Bearded Vultures’ home ranges and their conservation status. FS occurred in relatively large number (more than three hundred) in the study area, spatially distributed in a very heterogeneous way. Sedimentary or metamorphic rocks dating from the Palaeozoic Era (–541 to –252 million years ago) hold majority of them, with schists being the predominant rock type (62.1%). FS were near absent from limestone massifs of the North-Pyrenean zone and from granite formations of the axial zone. We found evidences of use by Bearded Vultures in a limited number of sites (n = 27 out of 339 localised FS). These colouring sites were characterised by steep slopes, intense coloured iron oxide deposits and a location usually close to the forest edge. Availability of colouring sites for breeding Bearded Vultures (n = 32 pairs or trios in the study area) was high enough: we localised a mean of 36.9 available FS and 2.6 used FS in a 15 km-radius around the usual breeding site of each pair/trio. The mean distance between a breeding site and the nearest known colouring site was 8.8 ± 0.86 km, a minor flight distance for this species. The conservation status of the used FS seems generally satisfactory, although one site disappeared due to drought and three others were damaged by domestic livestock trampling or wild ungulates. The vicinity of cables or fences, i.e. potential mortality factors, also concerns three of the used FS. We recommend to consider these colouring sites as key resources for the species and to protect them from any damage.