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Thaddeus R. McRae and Steven M. Green

Eastern gray squirrels produce moans for aerial predators and quaas for terrestrial threats. One commonly-supported hypothesis for such predator-associated signals is that they elicit predator-specific escape responses in conspecifics. With simulated aerial predators, squirrels ran to the far side of tree trunks. In response to simulated terrestrial predators, squirrels frequently ran to where they could see the predator but could quickly flee to the far side of the tree trunk. Playbacks of quaas and moans elicited flight behaviour, but without association between escape location and alarm call type. Locations elicited by alarm calls differed from those elicited by simulated predators, with squirrels pausing on the side facing the call’s source. While grey squirrel alarms and escape strategies differ by predator type, the vocalizations do not function to elicit divergent escape strategies in conspecifics. This result stands in contrast to observed functions in other species with calls differing by predator type.

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Thaddeus R. McRae and Steven M. Green

Threat-specific vocalizations have been observed in primates and ground squirrels, but their contemporaneous usage with visible signals has not been experimentally analyzed for association with threat type. Here we examine the eastern gray squirrel, an arboreal squirrel that uses both vocal and tail signals as alarms. Squirrels were presented with cat and hawk models simulating natural terrestrial or aerial predator attacks and also with control objects that do not resemble predators but approach in a similar manner. Individuals responded with tail signals (twitches and flags) and vocalizations (kuks, quaas and moans), but only flags and moans are associated with predator type. Moans were elicited primarily by aerial stimuli and flags by terrestrial stimuli. Eastern gray squirrels use an alarm-signaling system in which signals in each modality potentially are associated with particular attributes of a threat or may be general alarms. Terrestrially-approaching stimuli yielded vocal and tail alarm signals regardless of whether the stimulus resembled a predator. With aerially-approaching stimuli, however, quaas were used more often when the stimulus resembled an aerial predator than when it did not. An approaching object’s physical appearance may therefore affect squirrels’ responses to aerial, but not terrestrial, objects. When the stimuli resembled real predators approaching in the natural manner (terrestrially or aerially), both tail flags and vocal moans were associated with predator type, so we also considered moans and flags together. The presence and absence of moans and flags in an alarm signaling bout yields a higher statistical index of predictive association as to whether the threat is aerial or terrestrial than does either component alone.