Precocious Sexual Development in the Juvenal

In the course of trapping English Sparrows (Passer domesticus) in the Los Angeles area in the summer of 1952, three juvenal males with enlarged testes were taken. Histologic examination of the gonads of these individuals showed that all three were in breeding condition. In the descriptions of these juveniles, the following criteria of sexual maturity were used: 1. Bill color. The bill of Passer domesticus changes from light brown in sexually inactive males to black in breeding males (Keck, 1932: 158-159). 2. Size of testes. Measurements of juvenal testes were compared with the following ranges in testis size noted in twelve breeding males in adult plumage and with ossified skulls, collected between June 3 and July 6, 1952: left testis, length, 6-8 mm., greatest diameter, 4-6 mm.; right testis, length, 6-7 mm., greatest diameter, 5-7 mm. 3. Histologic examination of testes. Testes were fixed in Bouin’s fluid, prepared by the parafhn method, sectioned at 10 microns, and stained with Harris’s hematoxylin and eosin. The histologic stages in testis development outlined by Bartholomew (1949~438) and Blanchard and Erickson (1949: 266) were used as standards for comparison.