Abstract: Controversy exists regarding the nature of primate social relationships. While individual primates are frequently hypothesized to form enduring social bonds with conspecifics, recent studies suggest that relationships are labile, with animals interacting only over short periods to satisfy their immediate needs. Here I use data collected over 10 years on a community of chimpanzees, Pan troglodytes, at Ngogo, Kibale National Park, Uganda, to investigate whether male chimpanzees establish long-term social relationships and to determine the factors that affect variation in relationship quality and the stability of social bonds. Kinship and dominance rank influenced the quality of relationships. Maternal brothers and males of the same dominance rank class groomed each other more equitably than did unrelated males and males that were dissimilar in rank. In addition, males that formed strong social bonds groomed more equitably than did males that displayed weaker bonds. Social bonds were stable over time, with relationships in one year predicting those in subsequent years. Kinship and the quality of social relationships affected bond stability. Maternal half siblings and males that groomed each other equitably maintained longer-lasting bonds than did nonkin and males that groomed each other unevenly. Virtually all of the males established at least one enduring relationship with another individual. The most enduring bonds formed between a few pairs of maternal brothers and dyads that maintained balanced grooming interactions. These results indicate that male chimpanzees maintain long-lasting and equitable social bonds whose formation is affected by maternal kinship and the quality of social relationships.

Abstract: Laboratory and field experiments have shown that, as predicted by the marginal value model, starlings, Sturnus vulgaris, stay longer in a food patch when the average travel time between patches is long. A laboratory analogue of a patchy environment was used to investigate how starlings respond to rapidly fluctuating changes in travel time in order to find out the length of experience over which information is integrated. When there was a progressive increase in the amount of work required to obtain successive food items in a patch (experiment 1), birds consistently took more prey after long than after short travel times; travel experience before the most recent had no effect on the number of prey taken. Such behaviour does not maximize the rate of energy intake in this environment. The possibility that this is the result of a simple constraint on crop capacity is rejected as, when successive prey were equally easy to obtain up until a stepwise depletion of the patch (experiment 2), birds took equal numbers of prey per visit after long and short travel times: the rate-maximizing behaviour. A series of models are developed to suggest the possible constraints on optimal behaviour that affect starlings in the type of environment mimicked by experiment 1.

Abstract: Most animals must learn some of the behaviours in their repertoire, and some must learn most. Although learning is often thought of as an individual exercise, in nature much learning is social, i.e. under the influence of conspecifics. Social learners acquire novel information or skills faster and at lower cost, but risk learning false information or useless skills. Social learning can be divided into learning from social information and learning through social interaction. Different species have different mechanisms of learning from social information, ranging from selective attention to the environment due to the presence of others to copying of complete motor sequences. In vertical (or oblique) social learning, naïve individuals often learn skills or knowledge from parents (or other adults), whereas horizontal social learning is from peers, either immatures or adults, and more often concerns eavesdropping and public information use. Because vertical social learning is often adaptive, maturing individuals often have a preference for it over individual exploration. The more cognitively demanding social learning abilities probably evolved in this context, in lineages where offspring show long association with parents and niches are complex. Because horizontal learning can be maladaptive, especially when perishable information has become outdated, animals must decide when to deploy social learning. Social learning of novel skills can lead to distinct traditions or cultures when the innovations are sufficiently rare and effectively transmitted socially. Animal cultures may be common but to date taxonomic coverage is insufficient to know how common. Cultural evolution is potentially powerful, but largely confined to humans, for reasons currently unknown. A general theory of culture is therefore badly needed.

Abstract: We consider the effect of including energy costs on the optimal strategy for animals exploiting a depleting food resource. In the context of central place foraging this leads to the problem of what load size should be brought back to the central place. Two strategies are discussed: (i) maximize gross rate of energy delivery and (ii) maximize net rate of energy delivery. The optimal load size (or optimal patch time) for net maximizers is not always larger than for gross maximizers, as has been claimed. Instead, the difference in optimal load size has the same sign as the difference between metabolic rates of travelling and foraging. We point out that the influence of costs has not always been correctly incorporated in experimental tests of the theory.