Diet patterns of island foxes on San Nicolas Island relative to feral cat removal
Brian L. Cypher A E , Erica C. Kelly A , Francesca J. Ferrara B , Charles A. Drost C , Tory L. Westall A and Brian R. Hudgens D
+ Author Affiliations
- Author Affiliations
A Endangered Species Recovery Program, California State University – Stanislaus, One University Circle, Turlock, CA 95382, USA.
B Environmental Planning and Conservation Branch, Naval Base Ventura County, 311 Main Road, Point Mugu, CA 93042, USA.
C US Geological Survey, Southwest Biological Science Center, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA.
D Institute for Wildlife Studies, PO Box 1104, Arcata, CA 95518, USA.
E Corresponding author. Email: bcypher@esrp.csustan.edu
Pacific Conservation Biology 23(2) 180-188 https://doi.org/10.1071/PC16037
Submitted: 13 September 2016 Accepted: 1 January 2017 Published: 3 February 2017
Abstract
Island foxes (Urocyon littoralis) are a species of conservation concern that occur on six of the Channel Islands off the coast of southern California. We analysed island fox diet on San Nicolas Island during 2006–12 to assess the influence of the removal of feral cats (Felis catus) on the food use by foxes. Our objective was to determine whether fox diet patterns shifted in response to the cat removal conducted during 2009–10, thus indicating that cats were competing with foxes for food items. We also examined the influence of annual precipitation patterns and fox abundance on fox diet. On the basis of an analysis of 1975 fox scats, use of vertebrate prey – deer mice (Peromyscus maniculatus), birds, and lizards – increased significantly during and after the complete removal of cats (n = 66) from the island. Deer mouse abundance increased markedly during and after cat removal and use of mice by foxes was significantly related to mouse abundance. The increase in mice and shift in item use by the foxes was consistent with a reduction in exploitative competition associated with the cat removal. However, fox abundance declined markedly coincident with the removal of cats and deer mouse abundance was negatively related to fox numbers. Also, annual precipitation increased markedly during and after cat removal and deer mouse abundance closely tracked precipitation. Thus, our results indicate that other confounding factors, particularly precipitation, may have had a greater influence on fox diet patterns.
Additional keywords: deer mice, exploitative competition, feral cats, foraging ecology, precipitation
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