Abstract
The importance of daily light ration in the sexual cycle of certain birds is well established. Male English sparrows may be brought to full spermatogenic activity within 6 to 8 weeks during the fall and early winter by daily exposures of 6 to 7 hours (4 P. M. to 11 P. M.) to the light afforded by either a 60 or 100 watt incandescent bulb. 1 , 2 , 3 , 4 No significant gonadal response, however, is observed in female birds during a comparable period of exposure. Female response is considered in a subsequent publication.
The question has been raised as to the manner in which light brings about testicular hypertrophy in the bird. Ivanova 5 placed caps over the eyes of male sparrows exposed to increased daily light ration to determine the role of the eyes in the response of the testes to light. According to her interpretation, light rays exert their stimulating effect on the testis largely through the general body surface as the breeding season approaches (February and March). Benoit 6 , 7 performed similar experiments with ducks and concluded that light acts through the ocular region. The stimulating action of light was maintained even after the optic nerves were severed. Bissonnette 8 was unsuccessful in an attempt to ascertain whether added exposures of light affect capped starlings since the birds died as the result of handling.
Thirty-five juvenile male sparrows were used in the present study. Fifteen of these received 7 hours of additional light daily beginning November 5th. A second group of 9 birds was capped during the 7-hour light exposure. Nine caged birds and 2 specimens from nature served as controls.
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