Richardson's ground squirrel (Urocitellus richardsonii) alarm calls communicate response urgency and are referential (#8)
Alarm vocalizations of ground-dwelling squirrels have been argued to communicate response-urgency rather than referential information in that optimal escape strategies don't differ by predator type. A notable exception exists, however, for Gunnison's prairie dogs, where field-based experiments reveal fine-grained productional and perceptual specificity. We tested whether an exception also exists for Richardson's ground squirrels (Urocitellus richardsonii), which produce situationally-specific chirps in response to avian predators, and repeated whistles to threats on the ground. While repeated whistles modulate information regarding response urgency via variation in syllable repetition rate, the situational-specificity of chirp versus whistle production begs the question of whether receivers alter their response according to call type. We tested for perceptual differences by exposing 34free-living Richardson's ground squirrels to playbacks of both chirps and whistles. Chirp playbacks elicited a higher frequency of running, more pronounced postural change, and a greater proportion of time devoted to vigilance than whistle playbacks. Differential behaviour as result of disparate signals alone provides evidence that Gunnison's prairie dogs don't constitute a singular exception among ground squirrels in having evolved referential alarm communication. For Richardson's ground squirrels, referential and response-urgency communication exist simultaneously.