Mateo, J.M. & Holmes, W.G. 1999. Plasticity of alarm-call response development in Belding's ground squirrels (Spermophilus beldingi, Sciuridae). Ethology, 105, 193-206.
Plasticity in the alarm-call responses of Belding's ground squirrels (Spermophilus beldingi) may function to prepare young to respond appropriately to calls according to the predator environment and habitat in which young develop. To examine the extent to which anti-predator responses are sensitive to early rearing environments, we studied the development of behavioural responses to playbacks of alarm calls and non-alarm calls in free-living juveniles and captive juveniles housed in large outdoor enclosures. Compared with same-aged, free-living juveniles, captive juveniles were more likely to show an observable response t o playbacks, exhibited more exaggerated initial responses (e.g., enter a burrow versus freeze), and remained alert longer following playbacks. The influence of rearing history on anti-predator responses was limited to responses to auditory stimuli, as the two groups of juveniles reacted similarly to fast-moving visual stimuli. The responses of free-living juveniles appeared to be more discriminating than responses of captive juveniles, particularly following playbacks of calls associated with less immediate threat.
Mateo, J.M. & Holmes, W.G. 1999. How rearing history affects alarm-call responses of Belding's ground squirrels (Spermophilus beldingi, Sciuridae). Ethology, 105, 207-222.
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 versus freeze) and to remain alert longer following playbacks of alarm and non-alarm calls (M ateo & H olmes submitted). Two studies were conducted to identify the factors contributing to these response differences. Post-emergent 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 behaviour 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.