Editor's Note: Recent mitochondrial genetic data indicate that Carduelis is polyphyletic and that Acanthis spp. belong to different clade. See the 50th supplement to the AOU Check-list of North American Birds for details. Future revisions of this account will reflect this change.
A bright little bird of the high Arctic, rarely studied except in winter when it comes more into contact with humans, the Hoary Redpoll has 2-yr irruptive population cycles, similar to and linked to those of the Common Redpoll, when this species becomes more abundant at the southern edge of its wintering range. Such irruptions reflect seed availability in the normal range of these species. Much of the biology of the Hoary Redpoll is poorly known but undoubtedly similar to that of the Common Redpoll, whose company it often shares.
Adult males in fresh plumage have been likened to drifting snowflakes and resemble fluffy snowballs when perched. Dense, loose plumage provides extra insulation from the harsh conditions in which the Hoary Redpoll is usually found. The behavior and physiology of this species are well adapted for arctic winters and short breeding seasons. Study is particularly lacking in the northernmost parts of its range, where few other birds are able to remain throughout the year. How the Hoary can cope with the perpetual darkness of the arctic winter remains largely a mystery.
Redpoll taxonomy is not settled. Some Hoary Redpolls are difficult to identify because there is much individual variation within this species and overlap with Common Redpolls. Redpoll taxonomy in this account follows a conservative approach and recognizes 2 species: Common Redpoll, C. flammea, and Hoary Redpoll, C. hornemanni .