Kinship does not affect vigilance in Columbian ground squirrels (Urocitellus columbianus)

Abstract

Vigilance, a vital behaviour in prey species, is affected by many factors, including social group size and possibly the presence of relatives. Columbian ground squirrels ( Urocitellus columbianus (Ord, 1815)) show a group-size effect of reduced individual vigilance in larger groups owing to increased predator detection. Such groups are composed of both kin and nonkin individuals. We observed vigilance (raising head above shoulders while foraging) of yearling males and yearling and older females, and examined kin relationships that are learned in the natal nest (viz., uterine kin). We then tested for possible effects of kinship on vigilance and thus on the group-size effect. Because of the kin-biased behaviours and nepotistic alarm calls shown by ground squirrels in previous studies, we expected either a kin-cooperative influence on vigilance or a nepotistic asymmetrical effect on vigilance,. We found that the presence of kin (whether above ground or not) had little or no effect on vigilance. This lack of kin effect reveals that Columbian ground squirrels do not rely any more on close relatives than on unrelated group members for detecting predators. Thus, the presence of kin does not contribute to the group-size effect on vigilance.