A Method for Sexing Blue Grouse

Abstract

A method of sexing blue grouse (Dendragapus obscurus) in hand and in field has been found by the author, while studying this bird in Washington County, Idaho. With birds in hand, the method is simple, and of value where untrained personnel check the hunter's bag for sex. Sexes are differentiated by white feathers, tipped with bluish-black, around the cervical air sacs in the male, in contrast to barred grayish-brown feathers of that region in the female. The white feathers, inverted by the male in display, are found in about three rows on the upper side of the cervical air sacs and five to six prominent rows on the lower side. The feathers of the jugulum are whitish, also tipped with bluish-black, but are not as distinct as those on the sides of the neck. For Birds in Hand.-In stroking the side of the neck from the body toward the head, the feathers are artificially inverted and a male is indicated by a flash of white feathers. From inspection of thirty-two male blue grouse, in which white feathers around the cervical air sac were checked against gonads, only one was found which did not have white feathers. It was a juvenile male collected July 18, 1952. However, a smaller juvenile male collected July 10, 1952 had the sex-distinguishing white feathers, as did another juvenile male collected August 18, 1952. Sixteen of the males checked were taken by hunters during September, 1952; twelve were collected by the author and four were predator and road kills. In addition, forty-nine other males from hunters' bags showed white feathers. In these, gonads were not checked, but absence of barred feathers on head, nape, interscapulars (Ridgway and Friedmann (1946), and middle pair of rectrices were used to identify males (Pearson, 1936). Nineteen female blue grouse, whose sex was determined by inspection of gonads, failed to show white feathers when stroked along side of neck from body to head. Fifteen of these females were taken by hunters during September, 1952. Seventy-one additional female blue grouse, from the hunter kill of September, 1952, did not have white feathers in the cervical region. These females were not sexed by inspection of gonads, but by barred feathers on head, nape, interscapulars and central pair of rectrices. Since the only negative case was a juvenile male approximately six weeks old, the method is considered effective for sexing adult blue grouse in the hand during all months, and juveniles after the middle of August. For Birds in Field.-In life, the white feathers around the cervical air sac in the male frequently form a white streak along the side of the neck terminating in the shoulder region. At times the white streak is concealed. Its absence therefore is not indicative of a female. Many times, due to poor light and distance, the white streak is more easily distinguished than other sexual differences in plumage, especially when juveniles are present. In the current study, presence of the white streak has been used in the field as an aid to check sex of