Reproductive success under constraints: Does increased maternal activity during lactation offset poor habitat and individual quality in an income breeder?

Human‐induced environmental modifications may alter forage access and, hence, how animals manage energy trade‐offs during critical periods. Reproduction, especially lactation, is the most energetically costly process for female mammals. In income breeders that do not store body reserves, such as roe deer ( Capreolus capreolus ), this increased demand has to be offset by substantially increasing food intake. How females adjust their activity under modified environmental conditions to support offspring growth may ultimately influence their reproductive success.

To assess the relationship between energy‐ and time‐budgets with reproductive success at weaning, we investigated activity profiles during late gestation and lactation for 97 GPS‐monitored roe deer females in a heterogeneous agricultural landscape. We then evaluated the impact of individual attributes (i.e. age and body mass) and habitat quality (i.e. poor forest vs. rich agricultural habitat) on the link between activity patterns and reproductive success.

Activity levels were lowest during late gestation and peaked within the first month post‐parturition. Females that lost their fawn(s) returned to pre‐parturition levels within one month post‐parturition, whereas successful females maintained high activity levels until weaning. Activity levels thus likely reflected energetic needs linked to reproductive allocation in roe deer females.

Females that raised twins were not detectably more active than those that raised singletons, suggesting higher resource availability or more efficient resource acquisition in the former. Overall, reproductive success was descriptively similar across habitats (from 0.81 to 0.84) and between primiparous (0.8) and multiparous (0.83) females. However, successful females in poor habitats were more active during early lactation, while during late lactation, light and primiparous females were more active than heavy, multiparous females.

Our results suggest that increased activity levels, likely reflecting elevated foraging effort during the costliest reproductive stage in a strict income breeder, may partially explain the similar reproductive success of females across habitats of contrasting quality. These findings emphasize the importance of behavioural plasticity for a species strongly dependent on current food intake to support reproduction, likely underpinning the success of roe deer in colonising a wide range of human‐modified habitats across Europe.