INDIVIDUAL VARIATION IN THE ANTISNAKE BEHAVIOR OF CALIFORNIA GROUND-SQUIRRELS (SPERMOPHILUS-BEECHEYI)

California ground squirrels (Spermophilus beecheyi) have evolved behav ioral defenses against their two predators, the northern Pacific rattl esnake (Crotalus viridis oreganus) and Pacific gopher snake (Pituophis melanoleucus catenifer). This studies were used to examine individual variation in antisnake behavior as it might tar affected by selection operating on arousability, fear-fulness, and aggressiveness. In Study 1 the behavioral consistency of two litters of lab-reared juveniles w as examined at two age periods during encounters with a caged gopher s nake and domestic cat. Close-range investigation and tail flagging app eared to be governed by short-term motivational states that were not s trongly correlated across age. Age correlations revealed that individu al tendencies to throw substrate were relatively consistent for the sn ake and even more so for the cat. In Study 2, wild-caught adults were obtained from five sites where rattlesnakes and gopher snakes were abu ndant and from five sites where these snakes were rare or absent. Squi rrels in a seminatural laboratory setting were given balanced presenta tions of a caged rattlesnake and gopher snake separated by 5 days. Sna kes were recognized by all squirrels as potentially dangerous, irrespe ctive of experience, age, and selective regime. Substrate throwing als o was positively correlated for the two snakes in both groups of adult s, indicating that level of aggressiveness is a consistent component o f temperament not specific to species of snakes. Physiological arousal was not correlated strongly for the two snakes, but it was significan tly lower in squirrels from sites where snakes were abundant. This sug gests some specialization to reduce anxiety that possibly enhances tac tical decision making.