Habitat fragmentation provides a competitive advantage to an invasive tree squirrel, Sciurus carolinensis

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.

Distribution and diversity of squirrels on university and college campuses of the United States and Canada

Squirrels on North American college and university campuses have been the subject of much animated conversation in informal venues, but a systematic assessment of their distribution across this habitat type has not been undertaken until now. We collected reports of squirrel species’ presence and absence from faculty experts at 536 campuses in Canada and the continental United States, and found that squirrels are nearly ubiquitous on campuses (95% had at least one species, and 40% had three or more), but that only a select few species are common campus residents. Foremost among these is the eastern gray squirrel (Sciurus carolinensis—on 62% of surveyed campuses), followed by the eastern fox squirrel (Sciurus niger), eastern chipmunk (Tamias striatus), North American red squirrel (Tamiasciurus hudsonicus), and woodchuck (Marmota monax). Eastern gray and fox squirrels partition campuses with one another, both in their shared native/core range and on the West Coast. While these invasive eastern species are present on campuses on the West Coast, notably, contingency analysis did not provide evidence that they are the primary factor discouraging western gray squirrels (Sciurus griseus) from using these habitats. The inventory and analyses presented here can provide a basis for longitudinal studies both within and across campuses and may be productively combined with initiatives that involve students in research.