CENTRAL PLACE FOOD CACHING - A FIELD EXPERIMENT WITH RED-BACKED SHRIKES (LANIUS-COLLURIO L)

Red-backed shrikes (Lanius collurio L.) stored experimentally presented mice (Mus musculus L.) by reimpaling them on thorns of sloe bushes (Prunus spinosa L.) in the vicinity of the nest. Large mice (20 g) were stored further away from the nest than small mice (4 g), while the smallest mice (1 g) were transported directly to the nest and cut up there. Large prey required more round trips to deliver than smaller prey (4 g). Time to immobilize, load and deliver the prey and the proportion of undigestable tissue increased with prey size. Birds used stored prey as an alternative to hunting in other patches as expected from patch use models. The birds maintained a high rate of food delivery to the young by using stored mice during periods when their foraging success of natural prey was low. Several aspects of the shrike''s food storing behaviour are in qualitative accord with suggestions derived from models assuming maximization of energy delivery rate.