Changes in foraging behaviour of the Coal Tit Parus ater due to snow cover.

This paper studies the foraging behaviour of the Coal Tit Parus ater, a small passerine wintering in mountain coniferous forests in the Pyrenees. We compared tree site use and the foraging techniques of birds, (1) under snowy conditions, when snow covered the outer substrates of pines, and (2) under snow-free conditions. Under snowy conditions, birds foraged in the lower and inner parts of trees, using trunks and thick branches as their main foraging substrate. During normal, snow-free conditions, birds used upper and outer parts of trees feeding mainly on pine cones and needles. Movement patterns of individuals differed from one condition to the other. During snow free conditions, birds used more costly energy methods, mainly flight and hanging position, while in snowy conditions they used lower energy consuming methods, mainly hopping. Our results support Norberg’s hypothesis (1977) that when the prospects of obtaining prey increase, foraging methods requiring higher energy consumption can be used.

Brotons L., ARDEA 85 (2): 249-257