Ardea
Official journal of the Netherlands Ornithologists' Union

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Knox A. (1988) The taxonomy of Redpolls. ARDEA 76 (1): 1-26
The subspecies of the circumpolar redpoll complex are usually either treated as conspecific under the name Carduelis flammea, or as two species, the Common Redpoll C. flammea (including cabaret, islandica and rostrata) and the Arctic Redpoll C. hornemanni (including exilipes). The two most widely distributed forms are broadly sympatric and intermediates are said to be common. It was generally assumed that they were the result of hybridization. This constituted the main argument for conspecificity. After examination of museum skins, it is shown that the plumages of most subspecies are very variable. The patterns of plumage variation are partly obscured by differences due to wear and because males tend to be paler than females and adults tend to be paler than first-year birds. Several characters are taxonomically less informative than previously believed. The apparent intermediates are not hybrids; they are an artefact of over-narrow definition of specific characters. A review of the literature showed that, despite the high frequency of supposed hybrids in some populations, no confirmed record of interbreeding has ever been documented. The results of studies claiming to support redpoll conspecificity equally support their consideration as two species. Complex differences in the plumages, measurements, ecology and behaviour of Common and Arctic Redpoll are summarised. Differences of this nature are unlikely to be found within a freely interbreeding population. The flammea and hornemanni groups clearly behave as separate species, although they are very closely related and there may well be some localized hybridization (as yet unproven). Pale and dark birds, which are both present in the Icelandic breeding population, show only slight differences in their biometrics. This requires further investigation. The name holboellii is a synonym; representing long-billed individuals in the skewed bill-length distribution of nominate flammea. They may arise partly due to differences in food and feeding behaviour.


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