Ecosystem engineers show variable impacts on habitat availability for cavity nesters in South American temperate forests.

This article investigates how ecosystem engineers—organisms that create or modify habitats—influence nest availability and reproductive success of three secondary cavity-nesting bird species (Aphrastura spinicauda, Tachycineta leucopyga, and Troglodytes aedon) in temperate forests of southern Chile. Over 13 years, the study recorded 757 tree cavities produced mainly by insect/fungal decay and the bird Pygarrhichas albogularis, finding that cavity characteristics (entrance size, volume, height) were strongly associated with nest presence and, to a lesser extent, reproductive success. Habitat attributes such as tree density and canopy cover influenced nest presence for some species but had limited effect on reproductive outcomes. The findings highlight the variable but critical roles of different ecosystem engineers in providing nesting resources, suggesting that conservation efforts should focus on maintaining diverse tree conditions—including live unhealthy and dead trees—to support cavity-nesting bird populations in South American temperate forests.