Behavioural and morphological changes in the mallard and their relationship to plasma oestrogen concentrations.

Abstract

The seasonal behavioural and morphological changes of the male bird are well documented (Carpenter, 1932; Domm, 1939). In the mallard the post-nuptial moult into the 'eclipse' or cryptic, female-type plumage coincides with alteration in behaviour from active aggressive territoriality into a quiescent non-territorial phase, which lasts until the bird reassumes the characteristic male nuptial plumage in the autumn. Castration prevents the assumption of the eclipse plumage (Walton, 1937), but the effect is delayed for a year if castration is carried out before or during the breeding season. It would appear that a testicular product is involved. Höhn & Cheng (1967), using paper chromatography and spectrophotometry, found that the oestrogen content of mallard testes in the breeding season exceeded that of testes removed after the breeding season. In order to correlate plasma oestrogen concentrations of mallard with seasonal changes in plumage and behaviour, the following methods were used; the results are