Annual gonadal and adrenal cycles in the Eastern Rosella, Platycerus eximius, (Psittaciformes : Platycercidae)

Abstract

Gonadal development in the eastern rosella was investigated in samples shot approximately monthly for one year near Armidale, N.S.W. In the testes of males of all ages and social rank, spermatogenesis begins in September, and by December the testis tubules of all males are filled with sperm. The histological stages of spermatogenesis are described. The Leydig cells of the testis are smaller in autumn, when the testes are regressing, than in early summer, when the testes are maximally developed. Between first-year and adult males, no differences could be discerned in the rate nor degree of development of testis tubules and intertubular tissue, but the weight of first-year birds' testes at full spermatogenesis was less than that of adults. In at least some first-year females the ovaries develop and eggs are released. Adrenal glands of adult males are smaller than those of females and first-year males. The adrenal cortical cells of all birds, male and female, are larger during the breeding season than during the subsequent moulting period. The similarity of gonadal condition between first-year birds and adults, together with the small differences in adrenals, leads to the conclusion that the failure of first-year birds to breed is a behavioural rather than physiological phenomenon.