Influence of food subsidies on the foraging ecology of a synanthropic species in protected areas

The expansion of many synanthropic species is linked to changes in the abundance and distribution of human-derived foods, and understanding how food subsidies influence the foraging ecology of synanthropes can facilitate reducing impacts to rare species. We combined stable isotope analyses and radiotelemetry information to characterize space-use and dietary patterns in Steller's jays (Cyanocitta stelleri), a known nest predator of marbled murrelets, sampled at both campground and forest sites in California state parks. We classified jays into four groups based on patterns of space use: (1) campground (jays captured in campgrounds that predominantly used these areas), (2) periphery (jays captured in campgrounds that commonly used adjacent forests), (3) intermediate (jays captured at forest sites that made long-distance movements between forests and campgrounds), and (4) forest (jays captured and only detected in forests). In the most heavily visited park, human foods comprised more than half of the diet of campground jays based on stable isotopes; moreover, campground jays consumed a greater proportion of human foods than periphery or intermediate jays, which both consumed more human foods than forest jays. Campground jays exhibited a functional response to human foods as park visitation increased, and breeding individuals preferentially provisioned their young with human-derived foods. Based on space-use patterns of intermediate jays, we estimated that the ecological footprint of campgrounds extended 2 km beyond their spatial footprint. Thus, the impacts of seemingly spatially constrained human recreational activities can have spillover effects on animal communities at relatively broad spatial scales within protected areas.