Movement simulations reveal both memory and social information drive individual foraging site fidelity in gannets

Alongside their direct perceptions of prey, Northern gannets (Morus bassanus) likely derive foraging cues from memory of previously successful foraging areas (private information), and from conspecifics (public information). Together these mechanisms are likely to underpin emergent Individual foraging site fidelity (IFSF) patterns, characterised by individual consistency in foraging area use. Where observation methods are inadequate in helping us determine IFSF properties, simulation experiments can help decipher the implicit foraging strategies present in an organism's movements.

We began by developing a movement simulation model to simulate spatially explicit foraging trips of chick-rearing gannets at Bass Rock, capturing direct perception of prey only. Once confidence in the foundational model was achieved, we made modifications to the model to incorporate various implementations of public and private information use in foraging strategies. The model outputs from simulations experiments, encompassing a wide range of complexity, were compared to several empirically derived patterns at the individual and population level, to gain insight into which mechanisms may be driving IFSF patterns and the potential consequences on a population's space use.

Patterns observed in standalone foraging trips were well represented by our movement simulations, permitting further developments to include public and private information use. Mechanisms using private information, namely memory based reuse of previously successful departure directions, were the primary drivers of IFSF. Incorporating social information refined these patterns, improving alignment with prey distributions and enhancing realism at the population-level, irrespective of the private information employed. However, mechanisms that best reproduced emergent individual and population level spatial patterns were associated with reduced foraging efficiency, inferred from longer trip durations and greater travel distances, indicating a trade-off between spatial segregation and short-term efficiency.

Our results support the idea that IFSF can emerge from hierarchical foraging strategies in which long-term private information structures broad-scale space use, while social information modulates fine-scale movements. By linking behavioural mechanisms to emergent movement patterns in a spatially explicit environment, our study illustrates how individual-based models can move beyond description to generate mechanistic and predictive insights into animal movement, improving our ability to anticipate responses to environmental change.