Cognitive Performance of Wild Eastern Gray Squirrels (Sciurus carolinensis) in Rural and Urban, Native, and Non-native Environments

Enhanced cognitive ability has been shown to impart fitness advantages to some species by facilitating establishment in new environments. However, the cause of such enhancement remains enigmatic. Enhanced cognitive ability may be an adaptation occurring during the establishment process in response to new environments or, alternatively, such ‘enhancement’ may merely reflect a species’ characteristic. Based on previous findings that have shown ‘enhanced’ cognitive ability (i.e., higher success rate in solving novel food-extraction problems or, ‘innovation’) in Eastern gray squirrels (Sciurus carolinensis), a successful mammalian invader and urban dweller, we used an intraspecific comparative paradigm to examine the cause of their ‘enhanced’ cognitive ability. We conducted a field study to compare cognitive performance of free-ranging squirrels residing in rural and urban habitats in native (United States) and non-native environments (United Kingdom). By using established tasks, we examined squirrels’ performance in easy and difficult, novel food-extraction problems (innovation), a motor memory recall test of the difficult problem, and a spatial learning task. We found that the four groups of squirrels showed comparable performance in most measures. However, we also found that the native urban squirrels showed: (1) higher success rate on the first visit for the difficult problem than the non-native urban squirrels; (2) some evidence for higher recall latency for the difficult problem after an extended period than the non-native rural squirrels; and (3) learning when encountering the same difficult problem. These results suggest that the previously reported ‘enhanced’ performance is likely to be a general characteristic and thus, a pre-adaptive phenotypic trait that brings fitness advantages to this species in a new environment. Despite this, some cognitive abilities in gray squirrels such as solving novel problems has undergone mild variation during the adaptive process in new environments.

Vocalizations associated with predator-type do not elicit predator-specific escape responses in grey squirrels

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.