Repetitive calls of juvenile Richardson's ground squirrels (<i>Spermophilus richardsonii</i>) communicate response urgency

Abstract

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.

Asymmetrical interspecific communication of predatory threat in mixed‐species colonies of lesser kestrels (Falco naumanni) and jackdaws (Corvus monedula)

“…Taken together, these changes in frequency structure with model type are consistent with findings suggesting that nonlinear vocal phenomena convey greater response urgency than signals without such non-linearities (Blumstein et al, 2008;Townsend & Manser, 2011). Temporal properties, such as call rate, which have previously been implicated in the communication of response urgency (Baker & Becker, 2002;Blumstein & Armitage, 1997;Warkentin et al, 2001; Wilson & Mennill, 2011) did not vary according to model type in our study, and thus at least for the model types tested, response urgency appears to be encoded in the frequency rather than the temporal domain of jackdaw and lesser kestrel vocalizations.…”

“…Signals may ultimately become productionally specific (Blumstein, 1995;Macedonia & Evans, 1993) and thus unique to a particular stimulus situation, allowing functionally referential communication (Blumstein, 1999;Evans, Evans, & Marler, 1993;Farrow, Doohan, & McDonald, 2017;Manser, Seyfarth, & Cheney, 2002;Seyfarth et al, 1980). Further, in that different predatory stimuli impose varying levels of threat, and predators employ a variety of hunting tactics, signals may also vary according to Morton's motivation-structural rules (Morton, 1977), communicating response-urgency in a graded fashion via changes in call rate (Blumstein & Armitage, 1997;Warkentin, Keeley, & Hare, 2001), duration (Brudzynski, Bihari, Ociepa, & Fu, 1993), amplitude (Wilson & Evans, 2012), frequency (Leavesley & Magrath, 2005) or the incorporation of non-linearities (Blumstein, Richardson, Cooley, Winternitz, & Daniel, 2008;Townsend & Manser, 2011).…”

Call‐specific patterns of neural activation in auditory processing of Richardson’s ground squirrel alarm calls

“…Using this approach, differential expression between chirp receivers and controls was observed in the VMH and the FCOR, while differences between chirp receivers and whistle receivers were observed in the SCOL, MeA, PAG, and PVT. Notably, even with this exploratory approach, whistle receivers' Fos labeling did not differ from controls, consistent with the lower response urgency conveyed by whistles relative to chirps (Warkentin et al, 2001).…”

“…After two hours of habituation, squirrels were presented with either a whistle call, a chirp call, or no stimulus as a control. The playback tracks were adjusted to play for 2 min and contained 49 evenly spaced chirp or whistle syllables (0.426 syllable/s call rate; Sloan & Hare, 2004;Warkentin, Keeley, & Hare, 2001). All calls were recorded in 2010 and came from a set of 112 total syllables from three individuals of unknown sex that were unfamiliar to the subjects.…”

Central distribution of oxytocin and vasopressin 1a receptors in juvenile Richardson’s ground squirrels

“…Sociality in Richardson's ground squirrel is essential for their survival, as these rodents issue alarm calls warning conspecifics of potential threats, thereby reducing predation risk among call recipients (Davis, 1984;Yeaton, 1972). Responses to these alarm calls vary based on the social environment (Davis, 1984;Hare, 1998b), the individual caller's past reliability (Hare, 1998a;Hare & Atkins, 2001), the type of call (Davis, 1984;Sloan, Wilson, & Hare, 2005), and also the positional and urgency information encoded within alarm calls (Sloan & Hare, 2004Warkentin, Keeley, & Hare, 2001). Richardson's ground squirrels are seasonal breeders, with mating in mid-through late-March and young emerging from natal burrows in late May through early June (Yeaton, 1972).…”