Abstract

When foraging in a group, animals can either search for their food (produce) or wait until others find food and join their discoveries (scrounge). In this study, I investigate the geometric consequences of changes in the frequency of scrounging in flocks of ground-feeding granivorous spice finches, Lonchura punctulata. Individuals using the producer tactic may be more successful if they avoid others who may be scrounging. Conversely, scrounging individuals may be more successful if they are near potential producers. If this is so, flocks with high proportions of scrounging should be more compact than equivalent flocks with lower scrounging proportions, and, in addition, scroungers should be closer to the center of the group than producers. I tested these predictions by observing flocks of six spice finches as they foraged for hidden clumps of food on an aviary floor. I altered the proportions of scrounging effort in a flock and compared flocks in which I expected low proportions of scrounging to those in which I expected high proportions. As predicted, flocks were significantly more compact when the proportion of scrounging was higher. In addition, producers tended to be farther from the center of the flock than scroungers. This first empirical evidence shows that producer-scrounger tactics can influence the geometry of a group as well as interact with other factors, such as dominance and vigilance, to determine the spatial positions of individuals within a group.