| Summary: | Environmental heterogeneity shapes the uneven distribution of resources available to foragers, and is ubiquitous in nature. Optimal foraging theory predicts that an animal's ability to exploit resource patches is key to foraging success. However, the potential fitness costs and benefits of foraging in a heterogeneous environment are difficult to measure empirically. Heterogeneity may provide higher quality foraging opportunities, or alternatively could increase the cost of resource acquisition because of reduced patch density or increased competition. Here, we study the influence of physical environmental heterogeneity on behaviour and reproductive success of black-legged kittiwakes, Rissa tridactyla. From GPS tracking data at 15 colonies throughout their British and Irish breeding range, we found that environments that were physically more heterogeneous were associated with longer trip duration, more time spent actively foraging whilst away from the colony, increased overlap of foraging areas between individuals, and lower breeding success. These results suggest that in more heterogeneous environments, there is greater competition between individuals for finite resources, which comes at a cost to reproduction. Resource hotspots are often considered to be beneficial, as individuals can learn to exploit them if sufficiently predictable. However, we demonstrate here that such fitness gains can be countered by greater competition in more heterogeneous environments. Code_kittiwake heterogeneity R Code to calculate environmental heterogeneity and the links with foraging dynamics Environment Environmental variables at random locations around kittiwake colonies used to calculate environmental heterogeneity Kittiwake trip metrics and success Trip metrics, reproductive success and heterogeneity used in paper analyses Kittiwake.csv HMMbehaviours Proportion of time spent in forage/transit/rest Foverlap Overlap between individual foraging areas Fsize Size of individual foraging areas
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