Abstract
There has been extensive game-theoretic modelling of conditions leading to equilibria of producer–scrounger dichotomies in groups. However there is a surprising paucity of experimental evidence in wild populations. Here, we examine producer–scrounger games in five subpopulations of birds feeding at a socially learnt foraging task. Over four weeks, a bimodal distribution of producers and scroungers emerged in all areas, with pronounced and consistent individual tactic specialization persisting over 3 years. Tactics were unrelated to exploratory personality, but correlated with latency to contact and learn the foraging task, with the late arrivers and slower learners more likely to adopt the scrounging role. Additionally, the social environment was also important: at the broad scale, larger subpopulations with a higher social density contained proportionally more scroungers, while within subpopulations scroungers tended to be central in the social network and be observed in larger foraging flocks. This study thus provides a rare example of a stable, dimorphic distribution of producer–scrounger tactics in a wild population. It further gives support across multiple scales for a major prediction of social foraging theory; that the frequency of scroungers increases with group size.
Highlights
Social animals can often choose among various strategies to obtain resources
Producer –scrounger (P-S) models predict that social foraging tactics should be frequency-dependent, occurring with an equilibrium frequency in a given population [3]
By monitoring flocks of great tits feeding at foraging tasks, we show that individuals specialize on producing or scrounging, leading to a bimodal distribution of producer –scrounger (P-S) behaviour in each of five subpopulations over 2–3 years measured
Summary
Social animals can often choose among various strategies to obtain resources. One such strategy is scrounging, in which individuals exploit the time and energy investment of others rather than investing in finding or processing resources themselves. Producer –scrounger (P-S) models predict that social foraging tactics should be frequency-dependent, occurring with an equilibrium frequency in a given population [3] Such theoretical modelling has generally not predicted ‘how’ this frequency of scroungers should be attained; i.e. with all individual scrounging at the same evolutionary stable strategy level (monomorphic population), or as various mixtures of individuals with different specialized tactics in a polymorphic population [5]. An alternative, yet unexamined, way in which there could be covariation between group size and scrounging is by ‘reshuffling’ of individuals; for example, scroungers might choose to join larger groups or move between groups more often This could lead to a broader link between sociality and scrounging, if it results in scroungers inhabiting more central social network positions. Our study provides a comprehensive examination of the individual, social and group-level factors driving the distribution of scrounging behaviour in a wild population of socially foraging birds
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