The effect of interference competition and fear of predation on flock size and foraging strategies of UMBS birds.

Abstract

In this experiment we tested our model by observing whether an optimal flock size existed for birds at UMBS. Optimal flock size was considered to be the flock size having the highest reward rate (highest foraging rate). We then tested whether the optimal flock sizes differed in different habitats: an open field and a covered forest. We predicted that there would be a larger flock size in the covered site due to increased perceived predation risk from the Sharp-shinned hawk and the Cooper's hawk which prey on birds. Therefore, the difference in optimal flock size between the sites, according to our model, would be due to benefits as the costs are expected to be the same for both sites. We then asked whether birds actually foraged in optimal flock sizes. We predicted that the most frequent flock size would be the optimal flock size, which would provide birds with maximal reward in terms of feeding rate.