Precocious Sexual Development in the Juvenal English Sparrow

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.Descriptions of the juveniles.-Number14.Live-trapped at 1646 North El Molino Avenue, Pasadena, Los Angeles County, California, on June 21, 1952, by Mrs. Harold Michener.Autopsied June 21, 1952.The skull was completely unossified.The plumage is juvenal except for two white-tipped black feathers on the throat, scattered chestnut and black, or buff and black, feathers on the dorsum and scapular regions, and a preponderance of the lesser coverts chestnut.The maxilla is dark brown, the mandible horn color, tinged and tipped with dark grayish brown.Although not black, the bill is noticeably darker than that of a juvenile with testes measuring 1 mm.trapped on July 6, 1952.The left testis measured 5.5 x 4 mm., the right testis 4.5 X 4 mm.Histologic examination of the testes showed an abundance of mature sperm with corkscrew-shaped acrosomes; the sperm were in bundles located at regular intervals along the radii of the tubules.This condition corresponds to class VI ("full spermatogenic activity with many sperm") of Bartholomew, and to stage 7 ("breeding") of Blanchard and Erickson.Number 20.Live-trapped at 2134 Brawley Street, Los Angeles, Los Angeles County, California (this locality is 7 miles south-southeast of central Pasadena), on June 22, 1952, by William E. Mannatt and John Davis.Autopsied June 22, 1952.The skull was completely unossified.The plumage is mainly juvenal except for eight white-tipped black feathers on the chin and throat, six fresh gray feathers on the right side of the forehead, scattered buff and black feathers on the dorsum and scapular regions, and a preponderance of the lesser coverts chestnut.The entire bill is black (fig.1).The left testis measured 6 X 4 mm., the right testis -X 4 mm.(one end ruptured in removal).Histologic examination showed a condition similar to that described for number 14. Number 22. Live-trapped at 2134 Brawley Street, Los Angeles, Los Angeles County, California, on July 6, 19.52, by John Davis.Autopsied July 6, 1952.The skull was approximately one-fourth ossified.The plumage is juvenal except for six white-tipped black feathers on the throat, scattered buff and black, or chestnut and black, feathers on the dorsum and scapular regions, and all the lesser coverts chestnut.The chin feathers are being replaced, and the white tips of the new feathers are visible beyond their sheaths.The entire bill is black (fig.1).The left testis measured 5 x 3 mm., the right testis 4 X 3 mm.Histologic examination of the testis showed a condition similar to that described for number 14. DISCUSSION The presence of juvenal male English Sparrows in full breeding condition during the normal breeding season of the species is difficult to explain.That this is not a local phe-Condor, Vol.