PUBERTY IN EUROPEAN STARLINGS - CAN NESTLINGS PERCEIVE DAYLENGTH

Three experiments suggest that a prepubertal period exists in European Starlings Sturnus vulgaris before they reach full body size at 3 weeks of age. (1) Castrated male nestling Starlings were reared on short days, long days, or long days initially and transferred to short days at 2, 3, 6 or 9.5 weeks of age. The increase in plasma LH concentration signalling the acquisition of photosensitivity began at 7 weeks of age in young on short days or transferred to short days at 2 or 3 weeks of age. In young transferred to short days at 3, 6 or 9.5 weeks of age, the increase began 4 weeks after transfer irrespective of age. Thus daylength before 3 weeks of age had no effect on the subsequent rate of acquisition of photosensitivity. However, birds raised on constant short days did not moult, whereas birds transferred to short days at 3 weeks did begin to moult. So birds do appear to be able to distinguish short and long days before 3 weeks. (2) In nestlings thyroidectomized at 4 days of age, testicular growth began later than in birds thyroidectomized at 8 days. Yet birds thyroidectomized at 8 days did not moult, unlike birds thyroidectomized at 4 days and intact birds. Presumably earlier thyroidectomy further extended the prepubertal period during which birds were unable to respond to short days. (3) Birds thyroidectomized as nestlings showed no change in testicular size in response to change in daylength when 8 months old.