Self-control, that is, overcoming impulsivity towards immediate gratification in favour of a greater but delayed reward, is seen as a valuable skill when making future-oriented decisions. Experimental studies in nonhuman primates revealed that individuals of some species are willing to tolerate delays of up to several minutes in order to gain food of a higher quantity or quality. Recently, birds (carrion crows, Corvus corone, common ravens, Corvus corax, Goffin cockatoos, Cacatua goffiniana) performed comparably to primates in an exchange task, contradicting previous notions that birds may lack any impulse control. However, performance differed strikingly with the currency of exchange: individuals of all three species performed better when asked to wait for a higher food quality, rather than quantity. Here, we built on this work and tested whether the apparent difference in levels of self-control expressed in quality versus quantity tasks reflects cognitive constraints or is merely due to methodological limitations. In addition to the exchange paradigm, we applied another established delay maintenance methodology: the accumulation task. In this latter task, food items accumulated to a maximum of four pieces, whereas in the exchange task, an initial item could be exchanged for a reward item after a certain time delay elapsed. In both tasks, birds (seven crows, five ravens) were asked to wait in order to optimize either the quality or the quantity of food. We found that corvids were willing to delay gratification when it led to a food reward of higher quality, but not when waiting was rewarded with a higher quantity, independent of the experimental paradigm. This study is the first to test crows and ravens with two different paradigms, the accumulation and the exchange of food, within the same experiment, allowing for fair comparisons between methods and species. (Stevens & Stephens, 2010), ranging from foraging decisions (Kacelnik, 2003; reviewed in Stephens & Anderson, 2001) to social interactions, for example mate choice (Sozou & Seymour, 2003) or reciprocity in cooperative events (Stevens & Hauser, 2004). Going for the immediately available but less preferred option instead of postponing action in favour of an overall better but delayed reward is defined as impulsivity, whereas self-control refers to the opposite strategy (Ainslie, 1974;Kalenscher, Ohmann, & Güntürkün, 2006;Logue, Chavarro, Rachlin, & Reeder, 1988). Europe PMC Funders GroupFrom an economical point of view, the preference for a maximum payoff should be selected for (Noë, Hooff, & Hammerstein, 2001) 2005). It has been commonly suggested that temporal discounting is a critical factor in intertemporal decisions (Kacelnik & Bateson, 1996;Kalenscher & Pennartz, 2008;Stevens & Stephens, 2010). Accordingly, future rewards are subjectively rated less valuable the longer the delay until they are received, because delay is associated with uncertainty for realization of the benefits and probability of loss. Alternatively, it has been argued th...

1.The social decisions that individuals make, in terms of where to move, who to interact with and how frequently, scale up to generate social structure. Such structure has profound consequences: individuals each have a unique social environment, social interactions can amplify or dampen individual differences at the population level, and population-level ecological and evolutionary processes can be governed by higher-level ‘emergent properties’ of animal societies.2.Here we review how explicitly accounting for social structure in animal populations has generated new hypotheses and has revised existing predictions in ecology and evolution. That is, we synthesize the insights gained by applying ‘network-thinking’ rather than the utility of applying social network analysis as a methodological tool. 3.We start with what has been learned about the generative mechanisms that underpin social structure. We then outline the major implications that social structure has been found to have on population processes, on how selection operates and organisms can evolve, and on co-evolutionary dynamics between social structure and population processes. Finally, we highlight areas for which there is clear evidence that accounting for social structure will refine current thinking, but where examples remain scarce.4.Applying ‘network thinking’ in biology presents not only new challenges, but also many opportunities to advance different areas of research. Addressing the question of how social structure changes the biological relationships linking individuals to populations, and populations to processes, is revealing commonalities across scientific disciplines. In doing so, animal social networks can bridge otherwise disparate research topics and, in the future, we hope will allow for more unified theories in biology.

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