Linking energy availability, movement and sociality in a wild primate ( Papio ursinus )

Proximate mechanisms of 'social ageing', i.e. shifts in social activity and narrowing of social networks, are understudied. It is proposed that energetic deficiencies (which are often seen in older individuals) may restrict movement and, in turn, sociality, but empirical tests of these intermediary mechanisms are lacking. Here, we study wild chacma baboons (Papio ursinus), combining measures of faecal triiodothyronine (fT3), a non-invasive proxy for energy availability, high-resolution GPS data (movement and social proximity) and accelerometry (social grooming durations). Higher (individual mean-centred) fT3 was associated with increased residency time (i.e. remaining in the same area longer), which, in turn, was positively related to social opportunities (i.e. close physical proximity). Individuals with more frequent social opportunities received more grooming, whereas for grooming given, fT3 moderated this effect, suggesting an energetic cost of giving grooming. While our results support the spirit of the energetic deficiencies hypothesis, the directionality of the relationship between energy availability and movement is unexpected and suggests that lower-energy individuals may use strategies to reduce the costs of intermittent locomotion. Thus, future work should consider whether age-related declines in sociality may be a by-product of a strategy to conserve energy. This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.