The diet of the Chough (Pyrrhocorax pyrrhocorax) and the Alpine Chough (Pyrrhocorax graculus ) in the Alps : seasonality, resource partitioning and population density

Abstract

We investigated the diet of the Chough (Pyrrhocorax pyrrhocorax) and Alpine Chough (Pyrrhocorax graculus) during winter and spring in the western Italian Alps by faecal analysis. Earlier studies conducted in the same area of syntopy in summer and autumn (Rolando & Laiolo, 1997 ; Rolando et al., 1997a) have shown that diet and foraging behaviour of these species may often diverge, but it is especially in winter months that interspecific differences reach the highest levels. From December to May Chough diet mainly consisted of fly larvae and pupae, while Alpine Chough diet was found to be more variable overall, largely consisting of berries in winter and Arthropods and houseleek leaves in spring. Chough and Alpine Chough also differed in foraging times (the former staying longer in patches). The greater trophic flexibility of the Alpine Chough appears to result from its opportunistic behaviour which allows this species to exploit the resource that is more profitable in each month. Overall niche breadth values were virtually identical, with the two species feeding upon approximately the same number of resource items. However, since resources were often different, the overlap between the diet of the two species was close to zero in winter, increasing from March onward. Diets are discussed with respect to the different status of these species in the Alps. In particular it is suggested that the mainly vegetarian diet of the Alpine Chough might be associated with its high population densities while the insectivorous diet of the Chough might be associated with its low population densities.