Avian flocking reduces starvation risk: an experimental demonstration

Summary Theory suggests that variance in individual food intake is lower during group foraging. Consequently, group foraging can at times reduce starvation risk. In aviary experiments using green-finches we demonstrate how intake variability decreases during group foraging because individuals use feeding by flock mates as a cue to locate food (local enhancement). Flocking preferences of greenfinches responded to variance in energy gain as predicted by theoretical models for foragers attempting to reduce starvation risk. While energy budget was positive the greenfinches were risk averse and foraged socially. Their preference shifted towards more risk prone solitary foraging when kept on a negative energy budget. We conclude that time or energy net gains are not necessary for foraging groups to form, but reductions in starvation risk may be sufficient.