Migration and Reproductive Rhythm in Birds

Abstract

IN a previous letter (NATURE, April 4, 1925) a brief account was given of an attempt to break the annual reproductive rhythm in the Junco (Junco hyamelis) and to induce premature recrudescence of the gonads in the middle of the winter. It was suggested that migration might be dependent on the production of a hormone by the organs whilst in a certain stage of regeneration. Thanks to a research grant from the Royal Society, I have this winter been able to repeat and extend my earlier investigations. Nearly two hundred Juncos were trapped on their southward migration in the autumn and divided, as before, between two aviaries. The experimental one has been artificially lit since Oct. 1, beginning on the first day with 5 minutes after darkness, 10 on the second, 15 on the third, and so on. The controls got no artificial light. Their day was therefore decreasing, while that of the experimentals was increasing artificially at about the same rate as it would have been normally in1 the spring. Neither aviary is heated.