Pathogen-induced alterations in fine-scale movement behaviour predict impaired reproductive success.

Pathogens play an important role in ecosystems and may impair fitness-enhancing activities such as foraging. However, the sublethal effects of pathogens on host movement behaviour and their subsequent impacts on reproductive success are poorly understood. In this study, we used high-resolution tracking to examine the movements of free-ranging European starlings () associated with sublethal avian blood parasite infections. We found that naturally infected individuals displayed reduced foraging behaviour, remained closer to their breeding location, and selected lower-quality habitats. These patterns were associated with poorer body condition of adults and less favourable development for their offspring. These behavioural changes suggest physiological limitations imposed by infection, reducing parental care and reproductive output. Our results provide compelling evidence that pathogen-induced changes in fine-scale movement behaviour are linked to impaired reproductive success, further emphasizing the need for a movement ecology perspective in local host-pathogen dynamics.