Richardson's ground squirrels, Spermophilus richardsonii, produce both repetitive and non-repetitive antipredator calls. While many hypotheses have been advanced to explain non-repetitive calls, the function of repetitive calling has received relatively little attention. We presented juvenile Richardson's ground squirrels with a predator model at distances ranging from 1 to 8 m and recorded the subsequent repetitive calls on digital audiotape. The rate of calling was inversely correlated with the distance between the model and the caller, with distance explaining almost 24% of the variation in call rate. To determine whether call recipients use that information, we manipulated the intersyllable latency of a single repetitive call exemplar to form 3 test stimuli varying only in call rate. Across 16 Richardson's ground squirrel colonies to which these calls were broadcast, the proportion of squirrels assuming the highly vigilant, alert posture increased with the rate of the repetitive call presented. Hence, juvenile Richardson's ground squirrels appear to communicate the proximity and presumably the degree of threat posed by potential predators.

Richardson's ground squirrels, Spermophilus richardsonii, produce both repetitive and non-repetitive antipredator calls. While many hypotheses have been advanced to explain non-repetitive calls, the function of repetitive calling has received relatively little attention. We presented juvenile Richardson's ground squirrels with a predator model at distances ranging from 1 to 8 m and recorded the subsequent repetitive calls on digital audiotape. The rate of calling was inversely correlated with the distance between the model and the caller, with distance explaining almost 24% of the variation in call rate. To determine whether call recipients use that information, we manipulated the intersyllable latency of a single repetitive call exemplar to form 3 test stimuli varying only in call rate. Across 16 Richardson's ground squirrel colonies to which these calls were broadcast, the proportion of squirrels assuming the highly vigilant, alert posture increased with the rate of the repetitive call presented. Hence, juvenile Richardson's ground squirrels appear to communicate the proximity and presumably the degree of threat posed by potential predators.Résumé : Les Spermophiles de Richardson, Spermophilus richardsonii, émettent des cris anti-prédateurs répétitifs et non répétitifs. Alors que plusieurs hypothèses ont été avancées pour expliquer les cris non répétitifs, le rôle des cris répétitifs a été peu étudié. Nous avons mis des Spermophiles de Richardson juvéniles en présence d'un modèle de prédateur, à des distances de 1 à 8 m, et avons enregistré les cris répétitifs qui ont suivi sur ruban digital audio. La fréquence des cris était inversement proportionnelle à la distance entre le modèle et le spermophile, et la distance expliquait 24 % de la variation de fréquence des cris. Pour déterminer si les auditeurs des cris utilisent cette information, nous avons manipulé le temps de latence entre les syllabes d'un seul modèle de cri répétitif pour obtenir 3 stimuli expérimentaux ne variant que par la fréquence des cris. Dans 16 colonies de Spermophiles de Richarson auxquelles on a donné à entendre ces cris, la proportion des spermophiles qui ont adopté une posture d'alerte et qui sont restés très vigilants a augmenté en fonction de la fréquence du cri répétitif présenté. Les jeunes Spermophiles de Richardson semblent donc capables de communiquer la proximité et probablement aussi la gravité de la menace que posent les prédateurs potentiels.[Traduit par la Rédaction] 573Warkentin et al.

Alarm calls are emitted by Richardson's ground squirrels Urocitellus richardsonii in response to avian and terrestrial predators. Conspecifics detecting these calls respond with increased vigilance, promoting predator detection and evasion, but in doing so, lose time from foraging. That loss can be minimized if alarm call recipients discriminate among signalers, and weight their response accordingly. For juvenile ground squirrels, we predicted that the trade-off between foraging and vigilance could be optimized via selective response to alarm calls emitted by their own dam, and/or neighboring colony members over calls broadcast by less familiar conspecifics. Alarm calls of adult female Richardson's ground squirrels were elicited in the field using a predator model and recorded on digital audio tape. Free-living focal juveniles were subjected to playbacks of a call of their mother, and on a separate occasion a call from either another adult female from their own colony, or an adult female from another colony. Neither immediate postural responses and escape behavior, nor the duration of vigilance manifested by juveniles differed with exposure to alarm calls of the three adult female signaler types. Thus, juveniles did not respond preferentially to alarm calls emitted by their mothers or colony members, likely reflecting the high cost of ignoring alarm signals where receivers have had limited opportunity to establish past signaler reliability [Current Zoology 58 (5): 773-780, 2012].