Sexual Dichromatism in Two Species of the Columbidae

It is obvious that many birds exhibit sexual dimorphism of color. But the causal mechanisms resulting in sexual dichromatism have been well demonstrated for only a few species such as chickens and finches. Sex hormones control the plumage color and form in the brown leghorn (Greenwood and Blyth, 1938). Witschi (1935, 1937) and students have shown that within the weaver finches, three kinds of control are involved: sex hormones, gonadotrophic hormones, and genetic constitution. The auto-sexing varieties of chickens and geese (Hutt, 1949; Quinn, 1939) and of domestic pigeons reveal sex dichromatism by the time of hatching and in the first plumage. Auto-sexing refers to a genetic method of detecting sex in birds and requires a sexlinked gene with dosage effects easily detected early in the birds’ development. A wild species exhibiting auto-sexing is the Snow Bunting, Plectrophenax nivalis (Pitelka, personal communication). Auto-sexing is difficult to explain by known hormonal mechanisms, and relatively direct gene control of such sexual dichromatism is indicated (Hollander, 1942). Among the approximately 14 species of doves in the genus Streptopelia only one, the Dwarf Turtle Dove (StreptopeZia tranquebarica), exhibits marked sexual dichromatism. This dove is native to the Philippines, southeastern Asia, and India. Immature and female tranquebarica are “gray.” The mature male has a bluish head, with the color extending to the neck ring, and a reddish brown “back.” Several auto-sexing pigeons and tranquebarica were available from a pigeon colony housed in a barn by the Department of Genetics at the University of Wisconsin, Madison, Wisconsin, and since they seemed to represent opposite extremes of early and late dichromatism within the Columbidae the following experiments with hormones were conducted. The data on the domestic pigeon or Rock Dove (Columba Zivia) were collected in connection with another study (Miller and Wagner, 1955) in which the hormones were donated by Dr. W. H. McShan and the implants and some of the injections were made by Frederic H. Wagner.