A COMPARATIVE-ANALYSIS OF THE FORAGING BEHAVIOR OF THE CHOUGH PYRRHOCORAX-PYRRHOCORAX AND THE ALPINE CHOUGH PYRRHOCORAX-GRACULUS COEXISTINGIN THE ALPS

The foraging behaviour of the Chough Pyrrhocorax pyrrhocorax and the A lpine Chough Pyrrhocorax graculus was studied during summer and autumn in the western Italian Alps, We assessed feeding times, feeding rates and foraging techniques associated with different foraging habitats. The Alpine Chough is mainly a ground surface feeder, stays for a relat ively short time at a feeding site (on average 2.1 min) and feeds quic kly (on average 9.2 items/min), In contrast, the Chough is almost excl usively an undersurface feeder (digger and prober), stays at a feeding site twice as long as the Alpine Chough (5.4 min) and feeds four time s as slowly (2.2 items/min). These differences suggest that the degree of actual ecological overlap is almost as low as possible for two spe cies using the same Alpine pastures as foraging sites. Interspecific c oexistence has occurred through a clear differentiation of foraging st rategies and diets. The foraging efficiency (in terms of feeding rate) of the Alpine Chough was always higher than that of the Chough in all habitats where they occurred together. The Alpine Chough was more var iable in the use of foraging techniques and more diversified in the us e of foraging habitats than the Chough, In both species, juveniles fed less efficiently than adults; the foraging behaviour of the Chough is probably more difficult to learn than that of the Alpine Chough, Othe r data have also shown that the Alpine Chough is more opportunistic th an the Chough in using seasonally available food, Considering the abov e, we suggest that the foraging behaviour of the Alpine Chough is more flexible and, perhaps, better adapted to the high mountain Alpine env ironment than that of the Chough. Two hypotheses concerning the ultima te reason why the Alpine Chough and the Chough have evolved divergent beak morphology are discussed.