Home sweet home: fitness consequences of site familiarity in female black-tailed deer

Abstract

Individual animals strive to maximize fitness by gaining access to food while minimizing predation risk, and spatial knowledge of both forage resources and predation risks has long been presumed to be advantageous. Actual fitness benefits of site familiarity, however, have rarely been demonstrated. We placed GPS collars on 57 female black-tailed deer in coastal California over 4 years to track seasonal movements, determine home ranges, and monitor survival and cause of mortality. We used seasonal home ranges and core areas as measures of site familiarity and modeled how mortality risk varied with use of familiar areas, forage availability, age class, and elevational overlap with simultaneously collared pumas using Cox proportional hazards models. The use of familiar areas was the best predictor of mortality risk, and deer that had a 40 % probability of leaving their home range in a given week were four times more likely to die. Puma predation was the largest cause of mortality, and deer whose average weekly elevation was farther from the average elevation of pumas were less likely to die. While forage availability was not related to mortality risk, deer with lower forage availability were more likely to leave their home range during both summer and winter. Our results provide a rare example of fitness benefits associated with site familiarity and the use of familiar areas as a refuge from predation. The benefits of site familiarity are likely widespread in ungulates, especially when there are stable home ranges, complex habitats, and few cues of predation risk.