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 discover ed by others (producers). Producer-scrounger game models typically ove rlook the costs and benefits of patch exploitation, assuming instead t hat producers and scroungers abandon patches simultaneously once deple tion occurs. Here we develop an extension of the marginal value theore m of patch exploitation that includes the producer-scrounger dynamics and examine the propensity of a producer to abandon its patch before d epletion once scroungers arrive. We predict that early departures shou ld occur more often when expected searching time decreases and when co mpetition intensity in the patch increases. Competition intensity is e xpected to increase when more scroungers are present or when patches a re smaller. We tested these predictions using a within-subject experim ental design with six captive flocks of spice finches (Lonchura punctu lata), each composed of one producer and three scroungers. As predicte d, producers abandoned their food discoveries more frequently once scr oungers arrived when searching time was short, when more scroungers we re present, and when patches were small. The results show that the pro ducers of a patch often leave as scroungers join their food discoverie s because the payoffs from leaving exceed those from staying.