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The diversity of avian populations in the Madre de Dios region of Peru is currently threatened by deforestation and other anthropogenic factors. In this study we assessed differences in bird species composition in two major types of tropical forests: floodplain and terra-firme forest. Abundance of groups of behaviourally similar species showed a higher presence of certain feeding guilds in either floodplain forests or terra-firme forest, whereas no difference in species richness was found. Analysis of the relative reproductive investment (RRI) of these tropical birds showed significant differences between habitats and among families and feeding guilds. Comparison of these families and feeding guilds to their relatives in temperate regions showed that neotropical birds have a smaller RRI, due to both smaller clutch sizes and lower egg mass, even when there are more broods per season. Quantification of RRI as used in this study can be useful to indicate bird species' susceptibility to anthropogenic factors in various habitats.