Cooperative Fish and Wildlife Research Units Program: Michigan
Education, Research and Technical Assistance for Managing Our Natural Resources

As human development increases across the globe, wildlife are either pushed out of developed areas or adapt to survive in these novel, human-dominated landscapes. Many mammalian mesopredators, such as the Virginia opossum (Didelphis virginiana), have adapted to living alongside human development in order to take advantage of human-subsidized food, water, and shelter and may also benefit from being “shielded” by humans from their natural predators if those predator species are less able to coexist with humans or if they alter their behavior when living in proximity to humans (the human shield hypothesis). The human shield hypothesis has been used to explain the co-existence of dominant and subordinate mesopredators in some of North America’s largest cities. Our objective was to evaluate if patterns of Virginia opossum occupancy, abundance, and activity conformed to patterns consistent with the presence of a human shield. We used data from a coordinated continent-wide camera trapping study, Snapshot USA to estimate Virginia opossum occupancy, abundance, and activity and relate these measures to surrounding landscape and urbanization variables. We found that opossum occupancy was positively associated with an index of human activity (anthropogenic sound), although at very high levels of sound, opossum occurrence decreased. Furthermore, opossum in heavily forest areas were more likely to be detected in areas with nearby anthropogenic sound indicating a preference towards settling near humans. In areas with a high density of human housing, opossum relative abundance and predator abundance both increased suggesting that opossum were shielded from predators, whereas at low or moderate levels of housing density, opossum abundance did not increase although predator abundance did. We found that opossum were strictly nocturnal (99% of detections) and that they shifted their activity to being active earlier in the evening in the presence of high predator abundance. We found evidence that Virginia opossum are likely shielded by humans from their predators and this was most apparent when examining abundance and to some extent occupancy. These results help to explain why the Virginia opossum is such a successful urban-exploiter.