Breeding Age of Blue Grouse

Abstract

A blue grouse (Dendragapus obscurus) collected in the Blue Mountains of southeastern Washington on October 11, 1949 had molted all of its juvenile primaries. The absence of the outer two pair of juvenile primaries indicated an adult bird (one which had completed the post-nuptial molt). However, the well-developed bursa of Fabricius (19 mm. deep) indicated a bird of the year. Disagreement of these two age criteria raised the question: Does the blue grouse molt all primaries during its juvenile molt? Does this species retain its bursa longer than a year and hence not breed until it is two years old? Fourteen full-grown blue grouse, shot in the Blue Mountains in fall since 1949, have been carefully examined in an attempt to answer these questions. Table 1 shows total weight, bursal measurement and status of primary molt for each of the Blue Mountain grouse as well as for nine adults collected by Schottelius (1951) during the nesting and brood season in Okanogan County, northern Washington. Five grouse in the table had molted all juvenile primaries except the outer two pair and had bursal measurements from 18 to 20