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Reciprocal altruism, one of the most probable explanations for cooperation among non-kin, has been modelled as a Prisoner's Dilemma. According to this game, cooperation could evolve when individuals, who expect to play again, use conditional strategies like tit-for-tat or Pavlov. There is evidence that humans use such strategies to achieve mutual cooperation, but most controlled experiments with nonhuman animals have failed to find cooperation. One reason for this could be that subjects fail to cooperate because they behave as if they were to play only once. To assess this hypothesis, we conducted an experiment with monogamous zebra finches (Taeniopygia guttata) that were tested in a two-choice apparatus, with either their social partner or an experimental opponent of the opposite sex. We found that zebra finches maintained high levels of cooperation in an iterated Prisoner's Dilemma game only when interacting with their social partner. Although other mechanisms may have contributed to the observed difference between the two treatments, our results support the hypothesis that animals do not systematically give in to the short-term temptation of cheating when long-term benefits exist. Thus, our findings contradict the commonly accepted idea that reciprocal altruism will be rare in non-human animals.

When foraging in groups, animals frequently use either scramble or contest tactics to obtain food at clumps found by others. The question of which competitive tactic should be used has been addressed from two different perspectives: a simple optimality approach and a game theoretic approach. Surprisingly, both approaches make strikingly different predictions about how percapita frequency of aggression within groups should change as a function of food abundance and competitor density. Resource defense theory typically predicts dome-shaped relationships between the per-capita frequency of aggression and both food abundance and competitor density, whereas game theoretic models predict an increase in aggression with competitor density and a decline in aggression with increased food abundance. We developed a game theoretic model to explore whether the predictions of resource defense theory and the game theoretic approach can be reconciled. Our model assumes that players have different competitive abilities and can adopt roles of either finder or joiner that affect the quantity of food that can be gained from a food clump. In accordance with earlier game theoretic models, we predict an increase in aggression with competitor density when animals compete by pair-wise contests. However, when food clumps can be challenged by more than one competitor, both the costs and benefits of defending increase with competitor density, which results in a dome-shaped relationship between the two variables. Our model predicts that aggression should always decrease as the density of food clumps increases.

Behavioural decisions in a social context commonly have frequency-dependent outcomes and so require analysis using evolutionary game theory. Learning provides a mechanism for tracking changing conditions and it has frequently been predicted to supplant fixed behaviour in shifting environments; yet few studies have examined the evolution of learning specifically in a game-theoretic context. We present a model that examines the evolution of learning in a frequency-dependent context created by a producer -scrounger game, where producers search for their own resources and scroungers usurp the discoveries of producers. We ask whether a learning mutant that can optimize its use of producer and scrounger to local conditions can invade a population of non-learning individuals that play producer and scrounger with fixed probabilities. We find that learning provides an initial advantage but never evolves to fixation. Once a stable equilibrium is attained, the population is always made up of a majority of fixed players and a minority of learning individuals. This result is robust to variation in the initial proportion of fixed individuals, the rate of within-and between-generation environmental change, and population size. Such learning polymorphisms will manifest themselves in a wide range of contexts, providing an important element leading to behavioural syndromes.

Increased opportunities for information are one potential benefit of sociality. We apply this idea to the advantages of colonial breeding in bird species that are typically monogamous within a breeding season but often form new pair-bonds in subsequent seasons. Individuals may benefit from nesting in colonies at high density by identifying good-quality potential alternative mates among their neighbours. The opportunities for finding a better mating option are likely to increase with colony size and density. We tested this prediction with a comparative analysis of the association between mate fidelity and coloniality in waterbirds (wading birds and seabirds), where there is wide variation in both the degree of mate retention over consecutive breeding seasons and the degree of coloniality. We used two comparative statistical analyses, one based upon generalized least squares and the other based upon a continuous-time Markov model, to test whether the pattern of association between divorce rate and degree of coloniality was evidence for correlated evolutionary change in the two characters. We found a significant and positive association between divorce rate and the degree of coloniality in waterbirds. The probable ancestral state corresponds to a combination of a high degree of coloniality with no, or weak, mate fidelity. The reconstruction of the historical pattern of character origin and evolution indicates that the transition from a high to a low degree of coloniality occurred before the transition to higher mate fidelity.