Kin count: Social, physiological, and environmental correlates of annual survival in Belding’s ground squirrels

Long-term studies of free‑living animals provide opportunities to identify the traits and environmental conditions that predict survival under natural selection. Using over two decades of mark-recapture demographic data, we evaluated intrinsic, social and environmental predictors of annual survival in a population of Belding’s ground squirrels ( Urocitellus beldingi ), obligate hibernators that exhibit female philopatry and kin-structured social groups. We assessed the effects of age, sex, body mass, glucocorticoid physiology, reproductive effort, kinship and snowfall using sex-specific generalized linear mixed models and logistic regressions. Adult females had higher survival than adult males, whereas juveniles—particularly males—experienced the highest mortality. As expected, survival was strongly associated with body condition: heavier individuals and those with lower fecal glucocorticoid metabolites were more likely to survive. For the first time, we demonstrate that the number of relatives predicted survival in this species. That is, adult females’ probability of surviving to the next summer increased with the specific number of living female close kin, beyond the effect of kin presence alone. Male survival was unrelated to kinship. In contrast, juvenile females with more kin had lower survival, suggesting age‑specific trade‑offs associated with kin structure. Earlier emergence from hibernation improved juvenile survival and was also associated with successful adult female reproduction. Snowfall influenced survival through phenological pathways: lower snow before the active season was associated with earlier emergence and higher survival in adult females, while post‑season snow was not related to survival. Together, these results show that social structure, physiological state, and climate‑driven seasonal timing interact to shape annual survival in an obligate hibernator, with effects that vary by sex and life stage. Understanding these interactions will be increasingly important as snowfall declines across much of U. beldingi ’s range.