Producer-scrounger games in a spatially explicit world: Tactic use influences flock geometry of spice finches

Group-foraging animals can either search for their food (producer) or search for opportunities to join the food discoveries of others (scrounger). To maximize food returns, producers should distance themselves from potential competitors whereas scroungers should increase proximity to potential producers. We investigated the extent to which playing one or the other tactic affected an individual's location in captive flocks of ground-feeding spice finches (Lonchura punctulata) as they foraged for hidden clumps of food on an aviary floor. We constrained some individuals to use the producer tactic by pre-training them to find food hidden under lids. Constrained producers foraged significantly further from the center of flocks than constrained scroungers. Flocks with many scroungers were significantly more compact than flocks with fewer scroungers. The results are consistent with published simulations of spatially explicit producer-scrounger models and suggest that the use of producer and scrounger foraging tactics be included as a factor that affects an individual's position within foraging groups.