Do ovenbirds (Aves: Parulidae) hunt by expectation?

Abstract

We performed a laboratory study to investigate the problem of when a predator should terminate search in a given patch of prey and move on to the next one. Gibb's and Krebs' hypotheses of number and time expectation and Charnov's optimization model were tested. Two groups of ovenbirds (Seiurus aurocapillus) were trained to find two or four prey. Subsequently the prey densities were suddenly reversed. We found no evidence that birds hunted by number or time expectation. Similarly, they did not behave as predicted by Charnov's model. Birds rapidly learned to find prey in the patches. They avoided patches and areas within patches already searched. Thus, the decision of when to leave a patch may coincide with complete coverage. More time was spent per patch at the higher density. This was partly due to area-restricted searching, To the extent that ovenbirds form expectations of where to find food and search selected areas thoroughly, hunting by time expectation cannot be ruled out completely.