Prey Dynamics Before, During, and After Red Foxes Den on an Urban University Campus

Many mammals use dens seasonally to protect neonatal young from weather and predators. Carnivores often become central place foragers during denning, which can influence the local abundance of prey. We began monitoring a site with camera traps on the University of Illinois campus in Urbana, Illinois in February 2021, which a pair of Vulpes vulpes Linnaeus (Red Fox) started using for a den in March 2022. This provided a natural study to determine how the relative abundance of prey changed in relation to Red Foxes denning. Red Fox use of the camera trap site sharply increased when they began denning, with a peak of 17.2 visits/day in April 2022 compared to an average of 0.7 visits/day during non-denning months. Sylvilagus floridanus Allen (Eastern Cottontail) relative abundance was relatively steady from July 2021 through March 2022 (average of 0.9 visits/day), when their relative abundance decreased to no visits during April and May 2022 as Red Fox relative abundance peaked. Sciurus carolinensis Gmelin (Eastern Gray Squirrel) exhibited a similar pattern, with high abundance from September 2021 through March 2022 (average of 6.9 visits/day) before a substantial decrease to the minimum of 0.4 visits/day in May 2022 when Red Foxes were denning. Thus, Red Fox denning coincided with strong decreases in the relative abundance of Eastern Gray Squirrels and Eastern Cottontails – both key prey species of Red Foxes in the Midwestern USA. The pattern of prey dynamics at the den site resembled that at two nearby reference sites, but the fluctuations were stronger, especially for Eastern Gray Squirrels which exhibited a significant (p < 0.05) reduction at the den site but not at reference sites. Our study supports previous studies indicating that when animals shift their habits to become central place foragers, they can change the activity patterns of other wildlife species in the vicinity. Our results also suggest that denning activity could act as a localized pulse of predation risk that modifies prey dynamics in urban systems.