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The trill vocalization is given by eastern chipmunks (Tamias striatus) when being pursued by a predator. To examine the adaptive significance of this vocalization, we assessed the effects of sex, age, and distance from the burrow on the occurrence of the call. Chipmunks were released either 10 or 100 m from their burrow and chased by an experimenter to simulate a terrestrial predator. We found that adult females trill more often when released 10 m from their burrow (67% of 24 chases) than when released 100 rn from their burrow (14% of 21 chases). Adult males, on the other hand, showed no significant difference in their probability of trilling based on the distance from their burrows (45% of 20 chases at 10 m and 55% of 20 chases at 100 m). Adult females trilled more than adult males when released 10 m from their burrow (67% compared with 45%) but less than males when released 100 m from their burrow (14% compared with 55%). Juvenile females only trilled when released 10 m from their burrows (45% of 11 chases), and juvenile males did not trill at all. We attributed sex, age, and location differences in giving the trill vocalization to the effects of kin selection on antipredator behavior.
Key words: alarm calling; antipredator behavior, chipmunks, predation, refuge, Tamias striatus, vocalizations
Chipmunks give three distinct calls in the presence of predators: chipping, chucking, and trilling (Dunford 1970; Elliott 1978). Chipping and chucking are repeated calls given in series that may last up to 30 min and are given in the presence of terrestrial and aerial predators, respectively (Burke da Silva et al. 1994). The trill vocalization (trilling) differs from the other two call types in that it is short in duration and given primarily during pursuit by a predator, not simply when the predator arrives or is discovered (Burke da Silva 1994). On average, the trill vocalization consists of 6-11 separate, low-amplitude notes with a call duration of 0.20 0.037 s (Burke da Silva et al. 1994). Chipmunks respond to playback of the trill vocalization by becoming alert (Weary and Kramer 1995). Escape calls of this nature have not been well described in ground squirrels. However, a trill vocalization has been described for yellow-bellied...