Stand attributes and the abundance of secondary cavity-nesting birds in southern beech (Nothofagus) forests in south-central Chile

Abstract

The ecology of secondary cavity-nesting birds (SCN) has been a matter of great interest for many years throughout the world, in part because of the direct and strong relationship between the breeding biology of these species and the impacts of forest management on the availability of cavities. While there exists a great body of knowledge on the ecology of SCN in the Nearctic and Palaearctic regions, information from the Neotropics is scarce, in particular for the temperate forests. In order to describe the effect of forest stand attributes on the abundance of SCN, we conducted a two-part study in the coastal range of the Maule region, south-central Chile. First, using 40 point-count stations covering the entire range of Nothofagus forest conditions, we related forest-stand attributes to the density of four SCN (austral winter and spring 1999, 2000). Second, using a nest-box experiment (spring 1999, winter 2000), we tested whether cavities were limiting the density of SCN in a second-growth forest. Point-count data suggest no relationships between the abundance of all SCN and habitat attributes during the winter (both years), but a significant and positive association with canopy height, total foliage volume, mean stem diameter and abundance of cavities (estimated) during the spring (both years). At the individual species level, cavities did not enter into a stepwise linear regression model for most species (most significant predictors were canopy height and stem diameter) suggesting that either our definition of what an appropriate nest site is was wrong or that factors such as cavity spatial aggregation and territoriality may have obscured a potential relationship. The nest-box experiment showed that the density of Thorn-tailed Rayaditos (Apbrastura spinicauda, P < 0.05) and House Wrens (Troglodytes aedon, P < 0.01) was limited by nesting sites during the breeding season, but not during the non-breeding one.