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Abstract |
Studies by Rowan (1930 and preceding papers) and Bissonnette (1931, a, b, 1932, a, b, and preceding papers) and Bissonnette and Wadlund (1931) have shown that in juncos, canaries, crows and starlings, at least, among birds, the sexual cycle is conditioned to a great degree by daily light ration. Sexual activity in both males and females can be modified at will by altering the daily light ration with controlled electric lighting from ordinary incandescent bulbs. Gonad changes, controllable in this way, are closely correlated with migrations in juncos and crows, as demonstrated by Rowan (1930, and preceding papers), who, however, maintains that it is the added periods of muscular exercise, rather than the light, as such, that condition these changes, in spite of the fact that it is always the added light he uses, rather than exercise, to get his effects. Bissonnette disagrees, and holds it is the light that is the major factor in conditioning the changes in sexual cycles. It has been found, also, that intensity and colour, or wave-length, as well as daily period of light are factors in conditioning sexual activity in starlings, and the method of increase of light also plays a part (Bissonnette, 1931, b, 1932 ; Bissonnette and Wadlund, 1931). |
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Abstract |
1. Cases are given in which female ferrets, already coming into, or in, oestrus as the result of artificially increased lighting in winter and spring, underwent regression or were retarded in their activation by reduction of either intensity or duration of daily illumination.
2. In some cases activation was resumed when light time or intensity was increased again.
3. These results are taken to indicate that, in female ferrets, any inherent rhythm or cycle of sexual activity is modified either naturally or artificially by changes of the cycles of duration and intensity of the light to which they are exposed daily, and so made to correspond in phases with the seasons, or changed therefrom. The rising daily illumination in spring and the falling one in late summer and autumn probably accelerate and retard the sexual activity of the female ferret, or accelerate the onset of anoestrus in late summer and autumn.
4. The data on modification of sexual cycles or activity in ferrets, so far obtained, are consistent with these conclusions. |
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