Patch exploitation in a producer-scrounger system: Test of a hypothesis using flocks of spice finches (Lonchura punctulata)

Group foraging allows individuals (scroungers) to obtain food discovered by others (producers). Producer-scrounger game models typically overlook the costs and benefits of patch exploitation, assuming instead that producers and scroungers abandon patches simultaneously once depletion occurs. Here we develop an extension of the marginal value theorem of patch exploitation that includes the producer-scrounger dynamics and examine the propensity of a producer to abandon its patch before depletion once scroungers arrive. We predict that early departures should occur more often when expected searching time decreases and when competition intensity in the patch increases. Competition intensity is expected to increase when more scroungers are present or when patches are smaller. We tested these predictions using a within-subject experimental design with six captive flocks of spice finches (Lonchura punctulata), each composed of one producer and three scroungers. As predicted, producers abandoned their food discoveries more frequently once scroungers arrived when searching time was short, when more scroungers were present, and when patches were small. The results show that the producers of a patch often leave as scroungers join their food discoveries because the payoffs from leaving exceed those from staying.