THE EFFECT OF TESTOSTERONE PROPIONATE ON THE BLACK-CROWNED NIGHT HERON¹²

Abstract

DURING A STUDY of the social behavior of the night heron, Nycticorax nycticorax hoactli (Gmelin), previously reported (i), it was discovered that both sexes of this species undergo a marked increase in the pigmentation of the lores, lower mandible and buccal cavity, also a conspicuous vascularisation of the legs, during the breeding season. When both sexes of a species of birdundergo the same seasonal development of a secondary sexual character it has been assumed, as in the case of Larus ridibundus, that the male and female sex hormones were producing identical effects (2). The recent experiments of Witschi and Miller (3) on the starling, Sturnus vulgaris, however, indicate that a male hormone may be present in sufficient amounts in both sexes during the breeding season to be responsible for these second ary sexual characters. This discovery raises the question as to why the females of those species, which owe their secondary sexual characters to malehormone, do not develop male behavior.