It has been stated that no general breeding season can be discerned in the birds of evergreen forest in West Africa. No previous study in East African forest is available, but my information, derived from gonad state, moult, and song volume, as well as the number of occupied nests found, gives a different impression at Amani. With a few specific exceptions the forest birds there nest between the beginning of October and the end of February and then moult. Simultaneous wing-moult and considerable gonad enlargement are rare in forest birds, and actually rarer than in birds from less equable environments also in Northern Tanganyika.
My data indicate that at Amani on the average (all forest species) the gonads of the individual male remain much enlarged for about four months in the year, of the female for less than two. It also appears that the individual bird of both sexes takes at least two months to get through wing-moult.
Data from occasional collections in other forests in Northern Tanganyika make it probable that with local modifications a periodicity similar to that at Amani exists there also. Information, both published and unpublished, for other forests, from Chirinda (S. Rhodesia) to Mt. Elgon, suggests that a single well-marked breeding season is the rule throughout the East African mountain forests.
These results are discussed in relation to Beebe's at Kartabo and to the variables in the environment. I do not find any acceptable single-factor hypothesis.