Reproductive Rhythm in Birds

Abstract

IN the issues of NATURE for April 4, 1925, and Mar. 5, 1927, were given brief accounts of the effects of subjecting juncos (Junco hyemalis) during the autumn to artificially increasing days in place of the normally decreasing days of that time of year. It was shown that in spite of extremely low temperatures, recrudescence of the gonads could thus be induced in mid-winter. Ordinary electric light bulbs were used as the source of illumination. This indicated that the changes could probably not be attributed to radiation. During the past winter, through a renewed grant from the Royal Society, it was possible to repeat these experiments and to introduce variations. A full account of these is shortly going to press. Considered together, they suggested that the development of the gonads was due directly to increasing activity made possible through daily extension of the waking hours.