MORPHOMETRIC VARIABILITY IN REDPOLLS FROM CHURCHILL, MANITOBA

Two plumage forms were observed in redpolls from Churchill, Manitoba, which correspond to the putative taxa Carduelis flammea flammea (dark- plumaged birds) and C. hornemanni exilipes (pale-plumaged birds). In a sample of breeding adults (n = 277), we examined whether morphometric differentiation parallels this plumage polymorphism. Males and female s were analyzed independently, and age, date of capture, and status at measurement (study skin vs. live bird) were considered as covariates in univariate analyses. We used a separate phenetic analysis of plumag e characters, rather than our subjective field identifications, to est ablish the groups to be compared statistically; this ensured that mens ural characters (e.g. bill shape) were not utilized as classification criteria for the present investigation of metric traits. In both sexes , redpoll plumage forms differed significantly in three of seven exter nal mensural characters. Discriminant-function analyses, based on the same characters, showed that the forms can be distinguished morphometr ically with great confidence (jackknifed estimate of correctly classif ied individuals was 87% in both sexes). In males and females, the dist ribution of discriminant scores of typical individuals and of a set of unidentified birds is bimodal. In a bivariate-reduced space of plumag e and morphometric variability, pale- and dark-plumaged ASY (after-sec ond-year) males form distinct groups. In SY (second-year) males and in females, plumage forms are not strictly distinct, but in no case was there an abundance of intermediates as predicted under the hypothesis that the forms are distinct species that frequently interbreed. Redpol l types may be specifically distinct, as has frequently been suggested , but they also may be examples of intraspecific genetic or ecophenoty pic polymorphism. Experimental breeding and an assessment of mating pa tterns in the field are required to test these possibilities.