Sexing of redpolls Acanthis flammea in Iceland from morphometrics

Members of the redpoll complex are sexually monomorphic. Based on morphometric variation and molecular sexing of 209 redpolls Acanthis flammea from Iceland, males were found to be on average less streaked and larger than females. Generalised linear models were used to derive a general formula to sex the birds and to assess the relevance of different morphometrics (bill depth, bill length, wing length, body mass, tarsus length and plumage score). Plumage and wing length were the only measurements which contributed significantly to the final model. Of the individuals that were sexed by molecular assay, 68.3% could be sexed correctly by morphological analysis. Sex ratio deviated from parity in north Iceland and the ratio of sampled birds varied with the season: a female-biased sex ratio was observed during the winter, and three quarters of birds captured during the breeding season were male.