Testosterone-Induced Nuptial Feathers in Phalaropes

Although hormonal control of plumage dimorphism has been investigated in several species of birds, no study has been published on species in which the female wears the bright nuptial plumage and the male the dull plumage (Mathews, 1960).Typically the nuptial plumage of the male is more brilliantly colored than that of the female, although in many species, their plumages are quite similar.In the Phalaropodidae, Jacanidae, and Rostratulidae, however, the female is more colorful than the male and there is a reversal in the role of the sexes in courtship and incubation behavior (Gilliard, 1958).In order to determine what hormones, if any, are involved in the control of plumage dimorphism in phalaropes, experiments were conducted from June, 1961, through August, 1963, on captive Wilson Phalaropes (Steganopus tricolor) and Northern Phalaropes (Lobipes Zohatus) .Previous studies have shown that a wide variety of hormones may be responsible for the difference between male and female plumage in different species of birds.For example, the action of estrogen in domesticated Brown Leghorn chickens, pituitary and estrogenic hormones in certain African weaver finches, and androgens in the Ruff (Philomachus pugnax) have been shown to bring about sex differences (Witschi, 1961).In the phalarope, androgenic hormones, probably produced by the ovary, were suspected to be an essential factor in the development of the colorful female nuptial plumage, because the growth of this plumage is correlated with the onset of aggressive courtship behavior at the start of the breeding season.METHODS Cages and maintenance.-Totest the hypothesis that androgen produces the brilliant nuptial plumage in female phalaropes, Northern and Wilson phalaropes of both sexes were captured in northwestern Montana.Trapping was accomplished by a horizontal mist net method (Johns, 1963) or by the method of Serventy, Farner, Nicholls, and Stewart (1962).Sixty-one adult Wilson Phalaropes in nuptial plumage were captured in May and June of 1961 and 1962, and thirteen, eight of which were juvenal birds, were captured in May, June, and July of 1963.In addition, six Northern Phalaropes in winter plumage were captured in October, 1962.Many of these served as experimentals, a number served as controls, some were killed for anatomical studies, and a few were utilized exclusively in other experiments (Johns and Pfeiffer, 1963).All birds were maintained in individual cages for periods of time ranging from one to five months.Cages measured 24 x 16 inches in floor space and were constructed of wood covered by g-inch mesh hardware cloth.This gauge proved to be sufficiently small to keep the head of the bird inside while allowing the long, thin bill to pass freely through.Toenail loss and crippling, common to wild birds maintained in wire floored cages, was minimized by the use of several layers of newspapers over the cage floors.Each cage was provided with a small, flat water pan (8 x 12 x 2 inches) which was cleaned and refilled with fresh water twice daily at feeding times.