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Two Three-toed Woodpeckers

New research on mitochondrial DNA (mtDNA) sequences of Three-toed Woodpeckers Picoides tridactylus has suggested that it actually consists of two species (Zink, R M, Rohwer, S, Drovetski, S, Blackwell-Rago, R C & Farrell, S L 2002. Holarctic phylogeography and species limits of Three-toed Woodpeckers. Condor 104: 167-170). The analysis is based on 29 Three-toed Woodpeckers from 12 sites in Eurasia and North America. The study included five subspecies: P t tridactylus, P t crissoleucus and P t albidior from Eurasia and P t fasciatus and P t bacatus from North America. The results show that woodpeckers from Eurasia and North America form separate (monophyletic) groups. These groups differ genetically by about 4%, indicating that the two populations of Three-toed Woodpeckers have been separated for a long period. Robert Zink and his co-workers recommend formal taxonomic action and suggest that North American Three-toed Woodpeckers be separated as Picoides dorsalis. The new - and rather lengthy - vernacular names following this split become Eurasian Three-toed Woodpecker and American Three-toed Woodpecker, respectively. Within Eurasia, sequences were very similar and did not show geographic structure. The authors point out that this lack of structure across a large area points to a recent range expansion, perhaps following reforestation after the last ice age.
George Sangster