Testing the human shield hypothesis: female wild turkeys have greater fitness near human activity

Predator-prey dynamics are driven by trade-offs between resource
acquisition and risk avoidance, with prey behavior and fitness shaped by
both consumptive and non-consumptive effects. Human activity adds
complexity to predator-prey dynamics. Humans can either act as
super-predators through direct harvest or create refuge from natural
predators. The human shield hypothesis suggests that proximity to human
activity benefits prey by reducing predation risk, as predators tend to
avoid humans. In hunted landscapes where both predators and prey are
harvested, the benefits of the human shield may hinge on individual
behaviors. However, the role of consistent among-individual differences in
behavior (i.e., behavioral types) in influencing fitness, especially for
non-targeted females in male-only harvest systems, remains largely
unknown. Using GPS data from n = 200 female wild turkeys, we examined how
proximity to human activity (i.e., secondary roads) and predation risk
(i.e., shrub landcover) influenced survival and reproduction. Applying a
univariate modeling framework, we quantified variation in behavioral types
for both risk-taking measures and evaluated fitness outcomes to test
whether human activity functioned as a protective shield. We found
significant individual variation in both risk-taking measures (distance to
secondary roads— r = 0.39, 95% CrI = 0.35, 0.44; distance to shrub
landcover— r = 0.35, 95% CrI = 0.30, 0.40). Importantly, we found support
for the human shield hypothesis. Females that occurred closer to human
activity had greater fitness than females that occurred closer to risky
areas associated with predators. Consistent with the human shield
hypothesis, female wild turkeys also occurred closer to human activity
during critical nesting stages, such as incubation and brooding, which is
when predation risk is at its peak. Our findings indicate that human
activity can create a protective shield that deters predators and enhances
survival and reproduction for prey species of conservation concern.
Because habitat work on public lands often occurs in areas accessible to
heavy machinery, such as secondary roads, managers can pair habitat
manipulations with regular, light human presence in those locations to
improve survival and reproduction of subordinate species and deliver
strong conservation returns. Our results emphasize the need for further
research on the human shield hypothesis that explicitly incorporates
among-individual differences in behavior and links them to fitness, to
better understand how human recreation affects game populations.