The Importance of Arthropod Fallout on Snow Patches for the Foraging of High-Alpine Birds

The feeding habits of an alpine passerine bird community was studied during the breeding season in the Pyrenees (Northeastern Spain). Five of the six species often fed on arthropods found on snow, and their use of this resource increased with elevation. Two high alpine birds, Montifringilla nivalis and Prunella collaris, mainly used snow patches. Two species that primarily forage at lower elevations, Oenanthe oenanthe and Anthus spinoletta, preferred alpine tundra despite the fact that all species had higher foraging rates (both per unit distance and unit time) on snow. High foraging rates on snowfields can be explained by greater prey detectability and accessibility. A smaller size and thus lower profitability of snow arthropods compared with those of alpine tundra may be the reason why alpine birds preferred snow patches only at the highest elevations, where arthropod abundance in other habitats is very low.