Although it has long been recognized that many tropical birds do not share the same narrow breeding periods as temperate birds, conventional thinking considers tropical breeding seasons to be discrete periods generally governed by rainfall seasonality. We used a database of >31,000 captures of 104 species collected over 17 years in rainforest near Manaus, Brazil (2.5'S), to examine timing of breeding. The proportion of individuals with active incubation patches peaked at 7% in the dry season, from October through December. The peak was about twice as high as the lowest rate, in the late wet season (April—June). From 9 to 15 families and >20 species bred in every month. Many taxa did not conform to the general pattern, instead peaking in the wet season (e.g., Galbulidae, Sclerurinae, Grallariidae, and Formicariidae). Most well-sampled species, even those with strong seasonal peaks, bred at almost any time of year, a pattern also shown by some individual birds that were captured multiple times in breeding condition. Among the 10 species with >50 incubation patches, all bred in at least 9 months, and 7 bred in 11–12 months. Earlier results from the same data set showed extremely protracted molts that regularly overlapped breeding. Collectively, molt and breeding data suggest that the annual cycle of some equatorial birds, particularly suboscines, differs fundamentally from that of temperate species, with much less fixed timing of breeding.
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Vol. 130 • No. 3