Ageing red deer alter their spatial behaviour and become less social

Abstract Social relationships are important to many aspects of animals’ lives, and an individual’s connectedness may change over the course of their lifespan. Currently, it is unclear whether social connectedness declines with age, and what the underlying mechanisms might be, so the role of age in structuring animal social systems remains unresolved. Here, we describe senescent declines in social connectedness using 43 years of data in a wild, individually-monitored population of a long-lived mammal (European red deer, Cervus elaphus). Applying a series of spatial and social network analyses, we demonstrate that these declines likely occur due to a combination of within-individual changes in social behaviour and altered spatial behaviour (smaller home ranges and movements to lower-density, lower-quality areas). These findings demonstrate that behavioural changes can lead older animals to become less socially connected, shedding light on the ecological and evolutionary processes structuring wild animal populations.