Abstract
Migration of Birds and Sex Cycles.—By a series of experiments on the junco (Junco hiemalis connectens) Prof. William Rowan has shown that the rhythm of the reproductive organs can be interrupted almost at will by appropriate lighting conditions (Proc. Boston Soc. Nat. Hist., vol. 39, No. 5, 1929). He has thus succeeded in arresting the normal spring recrudescence of the gonads, in causing premature recrudescence in mid-winter, and by alternate over and under lighting causing a maximum recrudescence three times and a minimum reduction twice in the course of a normal single cycle of a year. Further, even in the absence of light, increasing periods of compulsory exercise cause a recrudescence of the gonads. It is suggested, therefore, that the increase of light permits increased exercise and that this is the crucial factor in inducing the development of the gonads. Birds which were released while the sex organs were in process of increasing or dwindling migrated, while those set free at the state of maximum or minimum development showed no inclination to move away. Rowan shows that the spring recrudescence of the sex organs cannot be due to rising temperatures, or the autumnal retrogression to falling temperatures, as has been supposed. While these conclusions apply primarily to the junco, he sees no reason to believe that it is exceptional.
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Research Items. Nature 125, 252–253 (1930). https://doi.org/10.1038/125252a0
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DOI: https://doi.org/10.1038/125252a0