Wild Carib grackles play a producer scrounger game

Producer–scrounger (PS) game-theoretical foraging modelsmake predictions about the decision of group-feeding animalseither to look for food (produce) or for opportunities to exploitthe discoveries of other foragers (scrounge). We report themost complete demonstration to date of the applicability ofthe PS foraging game in a free-living animal, the Carib grackle(Quiscalus lugubris) of Barbados. As assumed by PS games, thepayoffs obtained by scroungers were negatively frequency dependent.Experimentally, increasing the cost of scrounging led to a decreasein the observed proportion of scroungers, whereas raising thecost of producing increased the proportion of scroungers. Observationsof marked birds revealed that group-level changes could be broughtabout by individual flexibility in tactic use. Despite consistentindividual differences in tactic use, most birds used both tacticsand could alter their use of producing and scrounging when conditionschanged. We found no difference in the payoffs obtained by producersand scroungers, suggesting a symmetrical game equilibrium. Ourresults call for testing the PS foraging game in a broader rangeof biological systems that include different types of scroungingbehavior (e.g., scramble, stealthful, or aggressive scrounging)as well as the exploitation of different phases of food production(e.g., searching, handling).