Secondary Amazon rainforest partially recovers tree cavities suitable for nesting birds in 18–34 years.

This article investigates the restoration of tree cavities suitable for cavity-nesting birds in secondary forests undergoing passive succession in the central Amazon, Brazil, at the Biological Dynamics of Forest Fragments Project (BDFFP). The study found that cavity abundance increases with forest age but remains lower in 31–34-year-old secondary forests compared to old-growth forests, which have a higher density and greater diversity of cavity characteristics, including larger, deeper, and higher cavities important for large-bodied bird species. Land-use history (cutting only versus cutting and burning) did not significantly affect cavity availability. The findings suggest that several decades are needed for secondary forests to develop sufficient cavity resources to support diverse cavity-nesting bird communities, highlighting the importance of retaining legacy trees and old-growth patches to facilitate earlier recolonization.