Density, Territory Size, and Long-term Spatial Dynamics of a Guild of Terrestrial Insectivorous Birds near Manaus, Brazil

A .—From 1994 to 2003, I annually surveyed terrestrial insectivorous birds in a 100-ha plot within continuous rainforest near Manaus, Brazil. I used spot-map registrations and radiotagged birds to estimate territory size and density on the plot for 13 species. As in the few previous studies of Amazonian birds, territory sizes were large (mean = 13.0 ha) and densities were low (mean = 3.4 pairs per 100 ha). The most common species, Formicarius colma, was the only species with >10 pairs per 100 ha, and one of four species (with Myrmeciza ferruginea, Conopophaga aurita, and Corythopis torquatus) to have territories of <7.0 ha. On average, each species occupied 34% of the plot, with only four species (F. colma, Grallaria varia, F. analis, and M. ferruginea) ever occupying >50% in any year. Territories appeared and disappeared between surveys; ∼71% of territories detected in a given survey were present in the next survey. The two rarest species, Myrmothera campanisona and Hylopezus macularius, were absent from the plot in some years. Across species, territory stability was positively correlated with abundance; more common species had more stable density among years than rare species. Although past research has shown territory stability for the most common species of Neotropical rainforest birds, my results suggest that rarer species, which constitute the bulk of the avifauna, may show greater fl uctuation in abundance. I compared my results to similar data from lowland rainforests in Panama, French Guiana, Ecuador, and Peru. Species richness was lowest in Panama, but comparable among the Amazonian sites. Panama also had the highest biomass and smallest territory sizes. Interestingly, relative abundances of species shared among sites were not necessarily similar. With the exception of Conopophaga spp., all species or replacement species shared among sites were at least twice as abundant at one site as at another. Relative abundance within genera also diff ered among sites for Sclerurus and Formicarius. The sparse data available so far suggest that individual species show considerable spatial variation in abundance across Amazonia, though the mechanisms and the texture of the pa erns remain unknown. Received 30 May 2005, accepted 3 March 2006.