Abstract
Attention has recently been called to a relation between testicular hormones and some secondary sexual or “ambosexual” characters in several avian species, but it is still too early to say how widespread the observed reactions may be. In the English sparrow, Keck 1 has found the color of the beak an excellent indicator of the amount of testicular hormone circulating in the blood, while the plumage is not such an indicator; van Ooordt and Junge 2 find that in one of the gulls a testicular hormone is necessary for development in the male of colors in bill and feet which are found in both sexes during the breeding season; and Gallagher, Domm and Koch 3 report that injection of purified testicular extract restores the plumage of Sebright capons to its normal form and color. In light of these findings, and since plumage and eye-color of the male blackbird (Euphagus cyanocephalus) seem to be unaffected by the injection of theelin, 4 it was thought desirable to see if secondary sexual characters in the females of this species would respond to the male hormone.
The substance used for the purpose was an extract prepared from beef testes by the procedure of Gallagher and Koch. 5 Following the final acetone extraction, the material was in each case evaporated to a thick paste and injected directly or first taken up in olive oil. It proved to be somewhat irritating to blackbirds but was readily tolerated by capons on which it was tested and in which it produced the expected effects on comb and plumage.
Three tests were made on adult females weighing about 60 gm. each: one in July, just after the breeding season; one in August; and one in March.
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