Evidence of long-term declines in Island Scrub-Jay vital rates

Background/Question/Methods

Island species play important roles in local ecosystems, but they are undergoing unprecedented rates of extinction from a variety of threats including emerging infectious disease, invasive species, and climate change. These threats are of particular concern for island species, which have limited genetic or geographic ability to escape these threats. Little is known about the long-term population trends of the Island Scrub-Jay (Aphelocoma insularis), a species endemic to Santa Cruz Island in California’s Channel Islands. We used a 20-year mark-resight dataset and temporal symmetry models to describe long-term trends in Island Scrub-Jay adult population growth, survival, and recruitment, and to relate those trends to major drivers of island endemic extinctions (including disease, invasive species, and climate change). We used a variance components analysis to separate sampling and process variance.

Results/Conclusions

We identified population declines of ~1.8% annually that were driven by a reduction in adult survival in the later years of the study. While we found little evidence for impacts of disease and climate, we found some evidence that observed declines coincided with timing of an increasing wild turkey population but were not correlated with feral sheep or pig presence or eradication. We discuss these findings in the context of previous population estimates for this species and current management actions being considered to conserve the Island Scrub-Jay.