Juvenile Richardson's ground squirrels,Spermophilus richardsonii, discriminate among individual alarm callers

Abstract

Richardson's ground squirrels,Spermophilus richardsonii, issue vocal alarm responses to avian and terrestrial predators. Recipients of those calls presumably benefit from enhanced detection and subsequent avoidance of predators. If receivers of alarm calls differentiate among callers, they could use that information to tailor their behavioural response to the perceived level of threat. A neighbour's call may indicate more imminent danger than that of a non-neighbour; with individual recognition, recipients could adjust their response according to the reliability of the caller. I elicited and recorded alarm calls of juvenile Richardson's ground squirrels using an avian predator model. Series of five calls were then played back to focal juveniles in the field. Within each series, playbacks involved an initial ‘habituation series’ of four calls of either a neighbour or a non-neighbour. In ‘control’ series, the fifth call was from the same individual but differed from the four preceding it. In ‘experimental’ series, the fifth call was from a different individual than those played earlier. Juveniles showed greater vigilance in response to playbacks of neighbours’ calls relative to non-neighbours’ calls, but habituated rapidly to call playbacks, showing a significant decline in vigilance by the second call. In control series, a different call from the same individual did not significantly increase vigilance. In experimental series, a call from a different individual restored vigilance to a level similar to that recorded prior to habituation. These results suggest that juvenile Richardson's ground squirrels discriminate among callers and use that ability to respond differentially to alarm calls issued by neighbours and non-neighbours.