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Facteurs influençant les stratégies de recherche alimentaire des oiseaux marins : une approche comportementale

Abstract : It is essential to understand how animals make foraging decisions to acquire food in order to better anticipate their responses to environmental changes. Breeding seabirds make central-place foraging trips at sea, from their colony. The deployment of small GPS devices on them reveals that they travel for tens to thousands of kilometers, in search of prey for which very little information is known. The behavioural strategies they use to increase their chances to encounter prey, and the implications of these strategies with regards to human fishing activities remain open questions. This thesis offers to examine these questions in three chapters, through theoretical simulations, empirical analyses of foraging trips of various species and populations of seabirds, and the spatiotemporal matching of seabirds and fishing vessels movements. First, our random walk simulations indicate that straight-line phases within path are not sufficient to conclude that seabirds anticipate where to find their prey, contrary to previous conclusions proposed in the literature. However it is possible and easy to analyze biases in the directions individuals follow when they forage, to infer which sources of information they use to decide where to forage. Second, we compare individual fidelity strategies between species, populations and/or ecological contexts through the use of multivariate statistical models (GLMM). Many seabirds display individual fidelity in the direction they forage from the colony, suggesting they rely on memory. Our results show that this is also the case in different species and populations of tropical seabirds, where individuals can remain faithful to a foraging direction for several consecutive days. These results are surprising and difficult to explain as the species we studied are targeting prey whose distribution is supposedly very stochastic and ephemeral. It suggests that the use of memory might be much more widespread in foraging seabirds than anticipated, at least for decisions at large spatial scales. Finally, our analyses on the responses of albatrosses to fishing boats suggest that their responses can be modulated according to species and energetic constraints, and that encounters of fishing boats during a foraging trip have little influence on the strategy used by individuals on their next foraging trip. The attraction of albatrosses to boats might be mainly a local process (at the scale of the perception range) and may be largely opportunistic. Overall, our empirical results anchored in a solid theoretical framework suggest that seabird’s foraging cannot be summarized as encountering rare and unpredictable resources, but might imply resource selection processes after resources are encountered, and/or a decision as to rely either on memory or public information. With that regard, anthropic resources may only be one type of resources among others for seabirds. Many of the analytical tools used here could be transferred to other seabirds and other central place foragers. Indeed, a wider comparative approach is necessary to understand the complex variations in behavioural plasticity observed here, and their consequences regarding future environmental changes.
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Julien Collet. Facteurs influençant les stratégies de recherche alimentaire des oiseaux marins : une approche comportementale. Alimentation et Nutrition. Université de La Rochelle, 2018. Français. ⟨NNT : 2018LAROS025⟩. ⟨tel-02127243⟩



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