General mechanisms underlying the distribution and fitness of synanthropic predators in human-influenced landscapes remain unclear. Under the consumer resource-matching hypothesis, synanthropes are expected to distribute themselves among habitats according to resource availability, such that densities are greater in human-subsidized habitats, but mean individual fitness is equal among habitats because of negative density dependence. However, “under-matching” to human food resources can occur, because dominant individuals exclude subordinates from subsidized habitats and realize relatively high fitness. We integrated physiological, behavioral, and demographic information to test resource-matching hypotheses in Steller’s jays (Cyanocitta stelleri), a synanthropic nest predator, to understand how behavior and social systems can influence how synanthropes respond to food subsidies. Jays consumed more human foods at subsidized (park campground) sites than jays at unsubsidized (interior forest) sites based on stable isotope analyses. Jays that occurred at higher densities were in better body condition (based on feather growth bars and lipid analyses), and had greater reproductive output at subsidized than unsubsidized sites. Jays with breeding territories in subsidized sites maintained relatively small home ranges that overlapped with multiple conspecifics, and exhibited a social system where dominant individuals typically won contests over food. Thus, jays appeared to be under-matched to prevalent resource subsidies despite high densities and behaviors expected to lead to resource matching. Our results also indicate that local resource subsidies within protected areas can result in source habitats for synanthropes, potentially impacting sensitive species over broader spatial scales.
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Funding was provided by Save the Redwoods League, the College of Agriculture and Life Sciences (UW-Madison), the Department of Forest and Wildlife Ecology (UW-Madison), the Office of the Vice Chancellor for Research and Graduate Education (UW-Madison), the U.S. Fish and Wildlife Service, and the California Department of Fish and Wildlife. We thank numerous field and laboratory technicians for their dedicated efforts and California State Parks staff for logistical assistance.
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable institutional and national guidelines for the care and use of animals were followed. The research was conducted under animal ethics permit A01424-0-01-10 and scientific collection permit SC-011200.
The data sets analyzed during the current study are available from the corresponding author on reasonable request.
Communicated by Hannu J. Ylonen.
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West, E.H., Peery, M.Z. Behavioral mechanisms leading to improved fitness in a subsidized predator. Oecologia 184, 787–798 (2017). https://doi.org/10.1007/s00442-017-3898-0