Calling and Vigilance in California Ground Squirrels: Age, Sex and Seasonal Differences in Responses to Calls

Vigilance by California ground squirrels (Spermophilus beecheyi) following two kinds of naturally occurring "alarm" calls was examined. Chatters were usually singly emitted calls while repetitive calls were initiated by one or more chatters and continued with a variable, but long, series of "chats." During noncalling periods adults tended to be more vigilant than were pups (young of the year); adult male and female levels were similar, but males altered the time they spent in various forms of vigilance seasonally (before vs. after pup emergence). There was little evidence of age differences in vigilance elicited by either call type. However, prior to pup emergence, adult females had higher levels of bipedal vigilance to chatters than did males, but males had higher levels of vigilance to repetitive calls than did females. These differences disappeared after pup emergence. Repetitive calling has been shown to increase vigilance over that elicited by chatters alone. This effect was found to hold when adult males were examined separately and pups also tended to show the same result, but adult females did not. This may have been because females responded with high levels of vigilance to both types of calls.