HighlightsWe ask whether scrub-jays prefer earlier cache-retrieval when caching.Caching appears similar for trays that come back after 1 h, 25 h, and 49 h.Caching appears similar for delays of 7 min and 26 h when no choice of trays is provided.We find no evidence of a preference to cache in trays that are more accessible for recovery.

Western scrub-jays (Aphelocoma californica) live double lives, storing food for the future while raiding the stores of other birds. One tactic scrub-jays employ to protect stores is “re-caching”—relocating caches out of sight of would-be thieves. Recent computational modelling work suggests that re-caching might be mediated not by complex cognition, but by a combination of memory failure and stress. The “Stress Model” asserts that re-caching is a manifestation of a general drive to cache, rather than a desire to protect existing stores. Here, we present evidence strongly contradicting the central assumption of these models: that stress drives caching, irrespective of social context. In Experiment (i), we replicate the finding that scrub-jays preferentially relocate food they were watched hiding. In Experiment (ii) we find no evidence that stress increases caching. In light of our results, we argue that the Stress Model cannot account for scrub-jay re-caching.

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Niko Tinbergen (1963) described four complementary questions to be asked of any animal's behaviour in order to understand it. Two of the questions seek proximate explanations for behaviour: What are the material causes of behaviour? And how does the behaviour develop within the lifetime of an individual? These are questions of mechanism and ontogeny, and they are the primary focus of many psychologists and neuroscientists. While other chapters in this volume will explore at length the proximate causes of prospective cognition 1 , we will direct our attention to the other two questions, which concern the ultimate, evolutionary causes of prospection: function and phylogeny. Function and phylogenyEvolutionary explanations for an adaptation must enlighten on two key facts: first, the reproductive advantage that adaptation confers upon an individual animal ('function'); second, the constraints imposed on that adaptation by a species'

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