Abstract
Abstract. Hybridization with closely related taxa poses a significant threat to endangered subspecies (e.g. outbreeding depression, inbreeding) and confounds efforts to manage and conserve these taxa through a loss of taxonomic identity, in part because of the practical necessity of defining subspecies in a typological manner. We examined nine morphological characters in 167 post‐juvenile museum specimens to determine if loggerhead shrikes Lanius ludovicianus Linnaeus 1766 on San Clemente Island (off the coast of California) remain diagnosable as L. l. mearnsi Ridgway (1903); an island endemic listed as endangered by the United States Fish and Wildlife Service. Four recent shrike specimens from the island were compared to historical specimens using a bivariate scatter plot and a discriminant function (the latter was used to classify recent specimens post hoc). The few recent specimens were not diagnosable as L. l. mearnsi, but instead appear to be intergrades between L. l. mearnsi and L. l. anthonyi Mearns 1898 (the subspecies endemic to Santa Cruz, Santa Catalina, Santa Rosa and Anacapa islands), and are perhaps closer to pure anthonyi. Our data and the species’ natural history and distribution suggest that shrikes currently on San Clemente Island are the result of genetic ‘swamping’ of mearnsi by anthonyi. Under a necessarily typological definition of a subspecies, it is evident that mearnsi is probably no longer diagnosable. However, we conclude that protection of the entire Channel Islands population of the loggerhead shrike would be the best management strategy, as the species has declined drastically throughout the islands.
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