Nest site limitation and the community structure of cavity-nesters across an anthropogenic gradient in the Atlantic forest

COCKLE, KRISTINA; MARTIN, KATHY

Campos do Jordão, Brasil

Simposio; International Ornithological Congress; 2010

The production and loss of tree cavities are key processes structuring communities of cavity-nesting birds where nest sites are limiting, yet very little is known about how cavities are produced, or how long they last, in the tropical rainforests that harbour the highest diversity of cavity-nesting birds. Nest site limitation is supported by evidence from temperate forests, but several authors have suggested that it is an artifact of forest management, and that cavities are not normally limiting for populations of cavity-nesters in mature forest. Through a nest-box addition experiment in the subtropical Atlantic forest of Argentina, we determined that nest-sites limit the breeding density of secondary cavity-nesters (SCN) in both logged and primary forest. Although the Atlantic forest has a high diversity of both excavator and SCN species, excavated cavities made up only 20% of the cavities used by SCN. SCN depended primarily on cavities created by heart-rot decay in large live trees. Excavated cavities were in dead branches or dead trees and had a much lower probability of surviving from year to year. The critical nest site resource that maintains this diverse community of cavity-nesting birds appears to be cavities created by heart-rot decay in large live trees, because these cavities are available for use in multiple years.