Vigilance behaviour and use of rocks by Columbian ground squirrels

Abstract

During June and July 1986 at Skull Mountain, British Columbia, observations of Columbian ground squirrels (Spermophilus columbianus) were conducted to examine the relationship between vigilance behaviour and use of rocks. Most vigilance behaviour (looking and scanning) of Columbian ground squirrels occurs near burrows, and rocks near burrows are used to increase the distance of visibility, particularly following alarm calls. During both nonalarm and postalarm periods, adults and juveniles do not differ in the frequency of use of rocks, but do differ in how they allocate their time while on rocks. During nonalarm periods adults use rocks more for vigilance than do juveniles, whereas juveniles spend more time in other activities such as grooming and playing. After alarms, adults and juveniles on rocks spend almost equal amounts of time vigilant, but adults spend more time scanning (vertical posture with forepaws raised off the ground) while juveniles spend more time looking (head raised, but with forepaws on the ground). Ground squirrels use rocks more frequently during postalarm periods than during nonalarm periods and they prefer high rocks close to burrows. The observed patterns of rock use for vigilance behaviour suggest that risk of predation is an important constraint on the spatial and temporal allocation of activities by ground squirrels.