Estimating the population size of island loggerhead shrikes on Santa Rosa and Santa Cruz Islands, USA

Wildlife Society Bulletin
By: , and 



Island loggerhead shrikes (Lanius ludovicianus anthonyi) are an endemic, genetically distinct subspecies of loggerhead shrike on California’s Santa Rosa and Santa Cruz Islands. This subspecies is listed as a Species of Special Concern by the California Department of Fish and Game and has been petitioned for federal listing under the Endangered Species Act. Because of suspected low numbers and the possibility of federal listing, there was an urgent need to rigorously estimate the number of remaining individuals on the Islands. In 2009 and 2010, biologists from the U.S. Geological Survey and the National Park Service surveyed sample units on Santa Rosa and Santa Cruz Islands using a double-observer method with independent observers, where units were selected under a stratified random sampling design. Shrike abundance was estimated to be 169 in 2009 and 240 in 2010 for Santa Rosa Island, and 35 in 2009 and 42 in 2010 for Santa Cruz Island. These numbers, especially for Santa Rosa Island, are higher than previously reported but nevertheless are still low. Rapid vegetation change on both islands due to recent removal of non-native herbivores may threaten the habitat and status of this subspecies. In view of this circumstance and the still-low numbers of shrikes, additional intensive demographic and habitat-use studies are critical for obtaining information vital for the perpetuation of this subspecies.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Estimating the population size of island loggerhead shrikes on Santa Rosa and Santa Cruz Islands, USA
Series title Wildlife Society Bulletin
DOI 10.1002/wsb.108
Volume 36
Issue 1
Year Published 2012
Language English
Publisher Wiley
Contributing office(s) Fort Collins Science Center
Description 9 p.
First page 61
Last page 69
Country United States
State California
Other Geospatial Santa Cruz island and Santa Rosa Island
Online Only (Y/N) N
Additional Online Files (Y/N) N
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