Foraging strategy in a social bird, the alpine chough: effect of variation in quantity and distribution of food.

I conducted feeding experiments to determine the effect of variations in food availability on individual flocking behaviour and foraging efficiency in a social corvid, the alpine chough Pyrrhocorax graculus, which lives in large flocks all year round. In 37 trials I varied both food quantity and the number of food patches. A decrease in the amount of available food reduced the mean flock size, the proportion of birds that had access to food, and their mean pecking rate. A decrease in the number of patches, on the other hand, reduced only the proportion of birds that had access to food. The number of choughs foraging was not influenced by food competition but depended only on the number visiting the site. Females competed less well than males: when food was made scarce, they frequented the site in the same proportion as did males, but had less access to food. I suggest that in this social corvid, long-term advantages to flocking related to social bonds, such as the maintenance of pair bonds, may compensate for short-term costs such as a reduction in foraging efficiency. Copyright 1999 The Association for the Study of Animal Behaviour.