Influence of competitors on caching behaviour in the common raven, Corvus corax

Both territorial breeding common ravens and nonbreeding vagrants scatter-hoard carcass meat extensively. We show experimentally with four captive nonbreeders in a large semi-natural enclosure that common ravens alter their caching behaviour in the presence of conspecifics. When four birds were simultaneously given a small amount of food, which any one bird by itself could easily remove in several trips, all four birds decreased the latency to begin caching and increased caching speed. In contrast, when the four birds were given only enough food for a single individual to control, caching was greatly-delayed. If, as these results suggest, competition between conspecifics over food sources induces caching behaviour, then individuals should cache close to the food source to reduce travelling time and increase the time available to effectively compete for food in the presence of conspecifics. Here we show, that in the presence of competitors, common ravens instead cached further from the food source, provided they had space into which they could escape from the sight of the competitors. When escape from competitor vigilance was not possible, common ravens delayed caching and/or hid food when the competitor was preoccupied. A second factor that influenced caching behaviour was cache robbing; ravens not only recovered their own caches, but also:routinely recovered the caches they saw others make. (C) 1998 The Association for the Study of Animal Behaviour.