Territorial birds of prey adjust their flight behaviour over the course of the breeding season depending on their breeding success

Flight plays a central role in the life histories of birds but is extremely energy demanding. Reproduction is also associated with high energy demands. We might thus expect to see differences in movement behaviour between individuals that breed successfully, those that breed unsuccessfully, and those that do not breed, assuming that individuals adapt their movements in response to the constraints imposed by breeding. To investigate how the flight behaviour of individuals changes over the breeding season depending on breeding success, we used GPS‐tracking data of 59 territorials Bonelli's eagles Aquila fasciata , from the French population, collected between 2009 and 2023. While flight behaviours (range of movement, i.e. the spatial extent explored by individuals throughout the day, and proportion of time in flight) showed some variation resulting from breeding success, especially in females, it was less affected than we expected. However, after chicks had fledged, both male and female parents spent more time in flight than non‐breeders or unsuccessful individuals. This might be explained by individuals having invested so much in breeding by the end of the breeding season that to protect their investment they increase movement to ensure the survival of their young. Such behaviour may also be necessary for successful breeders to replenish the energy reserves used to rear their chicks. These results suggest that investing in reproduction may come at a significant cost to sedentary territorial birds, impacting their flight behaviour. However, the effect of this investment may only become apparent at the end of the breeding season, due to the accumulation of costs over time.