Morphological Homogeneity of a Population of Alaska Willow Ptarmigan

West, George; Savage, Susan; Irving, Laurence; Peyton, Leonard

The frequency distributions of wing length and tail length of 1200 Alaskan Willow Ptarmigan (Lagopus lagopus alascensis) were determined for each of the four sex-age classes collected form four localities in the Brooks Range of northern Alaska. None of the differences in any measurement within any sex-age class was statistically significant among the four localities within the Brooks Range. The monophasic frequency distribution and the lack of statistically significant differences in mean length within sex-age classes regardless of locality indicate that the sample is from a single homogeneous population. The four sex-age classes, however, have statistically significant different wing and tail lengths. Adult females exhibit less variation in length measurements than do the other age-sex groups. Sex was determined by a combination of wing and tail length measurements in our sample of adult Brooks Range Willow Ptarmigan with an accuracy of 94.4 per cent. For juveniles, sex was determined by wing length alone with an accuracy of 86.9 per cent in our sample, but the presence of brown pigment on the tail was not an accurate indicator of sex. Age can be estimated with 97 per cent accuracy using primary pigmentation. Juvenile birds (from three months to fourteen months of age) have the ninth primary tip darker than the eighth while adults (15 months and older) have the ninth lighter or equal to the eighth in pigmentation. The frequency of human error in measuring a series of wing and tail lengths was only 1.8 per cent, and there were no statistically significant differences in measurements made by three measurers. The amount of shrinkage due to drying of wings and tails averaged 0.7 and 0.8 mm, respectively. Therefore, when making comparisons with other populations, either fresh or dry material must be measured on both samples and not a combination of the two, or else the appropriate wet-dry correction factor must be applied to one set of data.

Morphological Homogeneity of a Population of Alaska Willow Ptarmigan

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