The development of alarm-call response behaviour in free-living juvenile Belding's ground squirrels

Abstract

The production of and responses to alarm calls by adult ground-dwelling squirrels has been widely documented, yet the development of alarm-call behaviours has not been systematically addressed. The responses of free-living Belding's ground squirrels,Spermophilus beldingi, to playbacks of conspecific (three alarm calls and juvenile squeals) and heterospecific (wren song) vocalizations were observed from natal emergence until the age of dispersal. Discrimination of the five auditory stimuli was not present at emergence but developed within the next 5 days, with responsivity to whistle alarm calls, indicative of fast-moving predators, developing earlier than to trill alarm calls, associated with slow-moving predators. Response patterns (response duration, vigilant postures and initial responses) changed throughout the following 4 weeks, and approximated adult responses before juveniles dispersed. Juvenile responses were indirectly influenced by conspecifics, particularly the dam, as well as by the physical environment, including distance from the natal burrow and location within the meadow. Alarm-call responses appeared to be adapted to the juvenile's current stage of development, with younger juveniles making a trade-off between information gathering and escape responses. The development of appropriate responses to each alarm call is hypothesized to be facilitated by observations of experienced ground-squirrels' responses. Despite their vulnerability, juveniles may not emerge with fully formed associations between alarm calls and responses if the local predator context changes over time, thus favouring plasticity in the response repertoire.