Effect of testosterone on testes, body weight and plumage regeneration in photorefractory male redheaded bunting Emberiza bruniceps.

Various doses of testosterone propionate (TP) were administered for 10 days to refractory male redheaded buntings exposed to 15L:9D in last week of June, shortly before the onset of molt, to determine the effect of exogenous male hormone on the testes, body weight and plumage regeneration in photorefractory birds. While 5-, 10-, or 25 micrograms of TP bird-1 day-1 did not affect the testes, body weight or feather regeneration, testicular growth was stimulated but body weight declined and plumage regeneration prevented in birds that received 150- or 250 micrograms of TP bird-1 day-1. In contrast, a 50 micrograms treatment, although unable to induce the growth of the testes, caused loss in body weight and feather regeneration. Also, a 25 micrograms dose of TP administered to photostimulated birds induced complete testicular atrophy. These results suggests that testosterone exerts dose-dependent effects on the testes, body weight and plumage regeneration in buntings. A positive correlation is found between the amount of hormone and the testes growth, while the increasing amount of hormone has negative effect on the body weight and regeneration of feathers.