Many shorebird species have widespread geographic distributions comprising several continents. Because shorebirds are excellent flyers and can migrate large distances, it is often unclear whether reproductive barriers between subspecies and populations from different continents exist. Kentish-Snowy Plovers (Charadrius alexandrinus) are cosmopolitan shorebirds. Whether the American and Eurasian subspecies-Snowy Plover and Kentish Plover, respectively—constitute a single species is the subject of a longstanding debate. We examined the divergence between American and Eurasian populations to reassess the current taxonomy by comparing genetic and phenotypic characters of the American subspecies C. a. nivosus and the Eurasian subspecies C. a. alexandrinus from seven populations. Genetic analyses revealed that American and Eurasian populations have strongly diverged, the Kentish Plover being more closely related to the White-fronted Plover (C. marginatus) than to the Snowy Plover. These results were consistent across all assessed nuclear markers (26 microsatellites and a partial CHD sequence) and two mitochondrial markers (ND3 and ATPase 6/8). Within subspecies, populations sampled across large geographic distances were not genetically differentiated (all Fst ≤ 0.01 and all Φst ≤ 0.06), which suggests panmixia. Snowy Plovers differed morphologically from Kentish Plovers, having significantly shorter tarsi and wings. Chick plumage and calls also may serve as diagnostic characters to distinguish Snowy and Kentish plovers, although more data are needed to quantify these differences. Our combined results suggest that the taxonomic status of C. alexandrinus needs to be revised, and we propose that Kentish Plover and Snowy Plover be recognized as separate species: C. alexandrinus and C. nivosus, respectively.
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Vol. 126 • No. 4