Juvenile, but not adult, Belding’s ground squirrels (Spermophilus beldingi) exhibit markedly different responses to alarm calls as a function of their environment. Compared with same-aged, free-living juveniles, captive juveniles (housed in large outdoor enclosures) are more likely to respond to playbacks, to exhibit more exaggerated initial responses (e.g. enter a burrow vs. freeze) and to remain alert longer following playbacks of alarm and non-alarm calls. Two studies were conducted to identify the factors contributing to these response differences. Postemergent rearing environments (such as the opaque enclosure walls that limited visual and auditory stimulation in captivity, or the increased number of conspecifics and natural alarm calls that free-living juveniles experienced) could not account for the majority of response differences between captive and free-living juveniles (Study 1). To determine if the attenuated responses of free-living juveniles were due to foraging pressures, we compared the behaviours of food-provisioned captive juveniles with those of non-provisioned captive juveniles. Although sample sizes were small, no differences were evident in the development or expression of responses as a function of foraging pressure. Next, the development of captive juveniles was compared with that of juveniles reared in the field but housed in captivity after emergence (Study 2). Differences in the response patterns of field-reared and captive-reared animals matched the differences reported previously, as the responses of field-reared animals observed in captivity mirrored those of free-living juveniles that remained in the field. Thus, the differences in alarm-call responses originally observed between captive and free-living juveniles are attributed to their pre-emergent, but not post-emergent, rearing histories.

Captive pups experienced levels of auditory, visual, tactile, and olfactory stimulation that were greater than those typically experienced by free-living pups. The increased exposure to conspecific alarm calls may have primed captive pups to respond more often and more intensely to the auditory stimuli they heard as juveniles. Sensitivity to early rearing environments may be adaptive for young ground squirrels if it facilitates the development of antipredator behaviour patterns that are appropriate for the local predator environment (e.g. openness of habitat, frequency of predators, availability of refuges).