The Bill of the Sparrow as an Indicator for the Male Sex Hormone. I. Sensitivity. ∗

Research on the male sex hormone has long been hampered by the lack of indicators which at the same time are sufficiently sensitive, inexpensive and simple from a technical viewpoint. Keck 1 reported the fact that pigmentation of the male sparrow bill depends on the presence of the male sex hormone. Using a preparation which had been extracted in our laboratory from male urine and standardized by the rat seminal vesicle test, he concluded that in the bill of male castrates as little as 1/15 of a daily rat unit gives a distinct reaction by the eighth day.

Since the sparrow can be kept with little expense even in small laboratories and the color change is so distinct and directly observable, it seemed worthwhile to investigate the availability of this reaction as a hormone indicator. We here report on a quantitative study, comparing the sparrow unit with the capon and the rat units.

Castration causing permanent depigmentation is easily performed in the sparrow. Even in the unoperated male, the bill is light brown outside of the breeding season, as is the bill of the female, with few exceptions, during the whole year.