Mesopredators retain their fear of humans across a development gradient

Anthropogenic impacts on wildlife behavior arise both from the immediate presence of people, which induces fear responses in many species, and the human footprint on the landscape (i.e., development), which affects animal movement and habitat use. Where both disturbance types co-occur, disentangling their impacts remains a challenge. Disturbance effects may interact such that species respond to increased human footprint by either reducing (habituation) or increasing (sensitization) avoidance of human presence. We experimentally manipulated perceived human presence, using playbacks of people talking, across a gradient of human footprint in California’s Santa Cruz Mountains and used camera traps to quantify the behavioral responses of bobcats (Lynx rufus), striped skunks (Mephitis mephitis), and Virginia opossums (Didelphis virginiana), mesopredators known to exhibit strong fear response to human presence, but which vary in their use of developed areas. Bobcats and skunks reduced activity in response to human playbacks but showed no change in responsiveness to playbacks across the development gradient, suggesting that these species are similarly fearful of humans at all development levels tested. Opossums exhibited a significant interaction between development and playback treatment such that reductions in activity level in response to human playbacks were strongest at higher levels of building density. Our results indicate that, rather than habituating to human presence some mesopredators retain a strong fear of humans or become more fearful when inhabiting more developed areas. We suggest that consistently high responsiveness to immediate human presence may benefit mesopredators living in human-dominated landscapes by mitigating the risk of anthropogenic mortality. Keywords: sensitization, habituation, ecology of fear, human impact, development gradient, playback experiment