LATERAL DISPLAY AS A COMBAT TACTIC IN RICHARDSONS GROUND-SQUIRREL SPERMOPHILUS RICHARDSONII

During fighting, adult ground squirrels frequently face each other lat erally, arch the back, and piloerect the tail. In a diurnal species, s uch distinctive visual cues seem consistent with the suggestion that t he lateral display serves a communicatory function. However, a detaile d analysis of videotaped sequences of free-living Richardson's ground squirrels from two consecutive mating seasons suggested that the later al maneuver has a functional role in combat. Because most agonistic en counters involve chasing, the rump is the principal body area bitten. When stationary, however, the opponent's rump is bypassed, and bites a re targeted at the shoulders. Defensively, a hip thrust is used to blo ck such attacks to the shoulder by pushing the opponent's head away. O ffensively, the lateral maneuver is used to push against the opponent, providing a vantage point from which to lunge at the opponent's shoul ders. In addition, the defender can launch counterattacks at the side of the head. The lateral orientation provides the attacker with a mean s of evading such attacks, by swerving laterally away. In some encount ers, both the offensive and defensive variations of the lateral maneuv er were used by both opponents, often simultaneously. Therefore, irres pective of the signalling function of the lateral display, much of its occurrence during combat can be explained in terms of its role as a c ombat tactic. (C) 1996 Wiley-Liss, Inc.