Photoperiodism and the annual testicular cycle of the bobolink (dolichonyx oryzivorus), a trans equatorial migrant, as compared with two temperate zone migrants

It is now quite generally accepted that seasonal changes in day-length play animportant role in the temporal regulation of several annual cyclic phenomena inmany birds of the northern hemisphere. Best known is the effect of photoperiodson the annual cycle of the testes, but evidence is accumulating that there is aneffect also on a metabolic cycle apparently peculiar to migratory species, aneffect perhaps on migration and perhaps also on the molt cycle (summarized inFarner, 1959).

WILLIAM L. ENGELS, Department of Zoology, University of North Carolina