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One way to quantify a prey’s response to a predator is by flight initiation distance (FID), the distance between a predator and prey at the moment the prey flees. As perceived risk from a predator increases, FID increases. Juvenile animals typically flee from approaching threats sooner than do adults because they have less able risk assessment. However, our observations suggested juvenile squirrels might use a different tactic: foraging near refuges. We first tested whether age affected squirrels’ FID in response to an approaching human on the UofL campus, where squirrels experience high levels of interactions with humans from an early age. We identified a focal squirrel’s age (adult or juvenile), and waited until it was within 5 meters of a refuge, i.e. a tree at least 6 meters tall. For all trials, the approaching person, focal squirrel, and refuge were in a straight line, with the squirrel between the person and the refuge. This arrangement and short distance to refuge facilitated flight decisions. A researcher approached each squirrel at 2 steps/second until the squirrel fled, and then measured 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 > 0.50). We then measured squirrels’ distances from trees while foraging, and we found that juveniles indeed compensated for low FID by by a different anti-predator behavior: foraging significantly closer to the refuge than adults. This is a novel finding among vertebrates.

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flight initiation distance, Sciurus carolinensis, foraging


Behavior and Ethology

Risk Assessment and Flight Decisions in Adult versus Juvenile Squirrels (Sciurus  carolinensis)