Risk assessment and flight decisions in adult versus juvenile eastern grey squirrels (Sciurus carolinensis)

One way to quantify a prey’s response to a potential predator is by measuring its flight initiation distance (FID). FID is the distance between an approaching predator and the prey at the moment the prey flees. As perceived risk from a predator increases, FID increases. Juvenile animals typically flee from an approaching threat sooner than do adults in part because they have not yet learned to assess risk correctly. We tested whether age affected squirrels’ responses to an approaching human in an urban setting, where squirrels experience high levels of interactions with humans from an early age. In our experiment, conducted on University of Louisville campus, we identified a focal squirrel’s age, and waited until it was within approximately 5 meters of a refuge. Refuges were trees at least 6 meters tall. For all trials, the approaching person, focal squirrel, and refuge tree were in a straight line, with the squirrel between the person and the refuge. This simple arrangement and short distance to refuge facilitated flight decisions. For each trial, the same researcher approached each focal squirrel at 2 steps per second. He dropped tokens to mark his starting location, the squirrel’s location, and his location when the squirrel initiated flight. He then measured the initial distance between predator (person) and prey, FID, and the squirrel’s distance to the refuge. Results showed no difference in FID between adults and juveniles (GLM analysis; p \u3e 0.05). The similarity of adult and juvenile responses is likely due to the high frequency of humans near squirrels at the campus study site. In addition, in the scenario we tested, the best escape route should have been immediately apparent, even for relatively inexperienced juveniles. Juveniles would likely have longer FIDs than adults in more complex scenarios requiring more difficult decisions