Effects of predation risk and patch quality on the formation and attractiveness of foraging groups of teal, Anas cressa

Abstract

The effects of changes in both predation risk and the quality of a food patch on the formation and attractiveness of groups of foraging teal were studied. Several predictions as to whether the predation-avoidance hypothesis or the food-finding hypothesis best explains goups foraging were tested by examining the decisions of teals flying over a food patch to land on the patch, with different combinations of the following variables: the presence of foraging teals on the patch; the predation risk; and the number of passing teals. Foraging groups already on the patch clearly attracted teals flying over it, but the atractiveness of very large groups decreased with a decrease in the quality of the food patch. The presence of a predator decxreased the landing frequency of passing teals. Landing on the empty patch was unrelated to the number of passing teals. In the presence of the predator, however, landing on the emply patch seemed to decrease more among solitary than among group flyiong teals. Overall, changes in landing frequency in relation to changes in patch emptiness. predation risk and number of passing teals did not support the predation-avoidance hypothesis of grouding for teals; support for the food-finding hypothesis of group formation and attractiveness was stronger.