Short days induce premature reproductive maturation injuvenile starlings, Sturnus vulgaris

Summary. Castration ofjuvenile and photorefractory adult starlings caused no immedi-ate increase in circulating concentrations of LH. In castrated juveniles and adults exposed to natural changes in daylength, plasma LH increased between mid-October and mid-November, although the increase was more rapid in adults. In castrated photo-refractory adults, plasma LH increased 3\p=n-\5weeks after transfer to artificial short days(8L:16D). In castrated juvenile starlings plasma LH increased 4\p=n-\6weeks after transfer to 8L:16D, irrespective of the age of the birds. Birds as young as 17 weeks had high LH concentrations. These results suggest that the reproductive system of juvenile starlings is in the same state as that of photorefractory adults, and therefore that activation of the hypothalamo\p=n-\pituitaryaxis for the first time in juveniles is analagous to the termination of photorefractoriness in adults