Leaf‐display and the sexual cycle in the Tooth‐billed “Bowerbird” ( Scenopœetes dentirostris , Ramsay).

Summary.1 The tooth‐billed “bowerbird” ( Scenopœetes dentirostris ) of North‐eastern Queensland clears a space on the floor of the rain‐forest and on this stage places freshly gathered leaves with their paler and more contrasting under surfaces uppermost. The indentations of the beak appear to be a development directly adapted to the laborious “sawing” by which the bird severs the petioles. The bird has not learnt that (at least with some of the leaves it uses) a sharp downward thrust would disengage the leaf from the tree without great effort. 2 Stage construction and leaf‐gathering commence at about the period when the testes begin their seasonal maturation. The stages are allowed to fall into disrepair after ovulation and at the time when the testes begin their fatty metamorphosis. 3 Male birds sit solitarily on a “singing stick” above each stage and sing loudly and continuously for several hours each day during the sexual season. This song, which includes the mimicked calls of other birds, ensures that in the rain‐forest where visibility is restricted every territorial rival or potential mate within a wide area will be aware of the singer's whereabouts. 4 It is not denied that the birds gain aesthetic pleasure from their leafdisplay and associated activities but it is concluded that these are essentially part of, and are governed by, the sexual cycle. The theory that the display grounds or bowers of this and allied species are primarily “recreational” in function is discounted. 5 Insufficient data are available to determine more precise functions of the display ground, or the factors that keep the reproductive rhythm “anchored” in time from year to year. These problems are discussed briefly in the text.