An empirical investigation of risk-sensitivity in foraging flocks of Nutmeg Mannikins (Lonchura punctulata)

Foraging in a group allows for the exploitation of other individuals' food findings, often modeled as a producer-scrounger game. Producer-scrounger games assume that searching for food patches (producer) and for exploitation opportunities (scrounger) are mutually exclusive tactics, and predict that the proportion of scrounger in a group should reach a stable equilibrium where both tactics provide equal payoffs. A stochastic producer-scrounger model assumes that scrounger reduces the variability of intake and that animals minimize the probability of incurring an energy shortfall (risk-sensitive). Consequently, it predicts that the proportion of scrounger at SEF should depend on the animals' energy requirement. In experiment one, I tested the crucial assumption that producer yields a more variable intake than scrounger. I observed flocks of Lonchura punctulata foraging for hidden patches of seeds on a board, in an indoor aviary. At a short time scale, producer yielded a more variable intake than scrounger in 17/20 birds. Based on the cumulative probability distributions of intake rates, scrounger frequency should decline with decreasing energy reserves, the opposite predicted by the stochastic model. In experiment two 7/8 birds reduced their use of scrounger with decreasing energy reserves. I conclude that L. punctulata is sensitive to the variability of intake rate (risk-sensitive), but that the current stochastic producer-scrounger model does not apply to these birds