Influence of resource subsidies on the foraging ecology of Steller's jays in protected areas

Background/Question/Methods

Populations of many native generalist species have increased as a result of anthropogenic landscape change and increases in the availability of anthropogenic food. These synanthropic species threaten less common native species through “spillover predation”, which occurs when synanthropic predators move into relatively unaltered landscapes where they prey on native species. As the expansion of many synanthropic species is closely linked to the prevalence of human-derived foods, understanding how spatial and temporal variation in food subsidies influence behavior and population processes is essential for controlling impacts to threatened species.

In California, populations of Steller’s jays (Cyanocitta stelleri) have increased dramatically in protected areas containing remnant populations of the threatened marbled murrelet (Brachyramphus marmoratus), presumably in response to the availability of human foods in recreational areas within these parks. The objective of this study was to understand how human-derived foods in protected areas containing remnant marbled murrelet breeding populations influence the foraging ecology of Steller’s jays. Specifically, we used stable isotope analysis of Steller’s jay tissue samples to estimate the importance of human foods in Steller’s jay diets, as well to determine (i) how the consumption of human foods varied among four state parks with different levels of human use and (ii) whether diet reflected seasonal changes in patterns of visitation. We also combined stable isotope analysis and radio-telemetry at one study park to determine how human-derived food resources influenced the movement patterns and territory spacing of individual Steller’s jays.

Results/Conclusions

Preliminary results indicate that human foods are an important component of the diet of Steller’s jays in park campgrounds, but varied in terms of park size and seasonally with human use. Preliminary results also indicate that individual jays that are enriched in human foods have small home ranges and exhibit greater home range overlap with conspecifics. Collectively, our work provides insight into the mechanisms by which in food subsidies within protected areas can increase the abundance of a synanthropic species that is a known predator of a high-profile endangered species.