Nest-site selection and community dynamics of cavity-nesting birds in a Neotropical forest

COCKLE, KRISTINA; MARTIN, KATHY

Edmonton, Alberta, Canada

Congreso; XXVII Meeting of the Society of Canadian Ornithologists; 2009

Society of Canadian Ornithologists

Birds that nest in tree cavities interact in a nest web, whereby some species (excavators) or processes (decay, damage) produce cavities, and others (secondary cavity nesters, SCN) depend on existing cavities. SCN should choose nest cavities with characteristics that optimize thermal properties and reduce the risk of flooding, predation, and usurpation; however, they are limited by the characteristics of cavities produced by excavators and decay proceses. From 2006 to 2008, we studied a community of cavity nesting birds in the subtropical Atlantic forest of Misiones, Argentina, and located 125 nesting attempts of 30 species in 78 cavities. SCN selected cavities that were deeper, were higher up, were on more isolated trees, had smaller entrances, and were less likely to have an upward-facing entrance than unused cavities, consistent with predictions that they choose cavities that reduce their risk of flooding and predation. In contrast to North American SCN that depend primarily on woodpecker cavities in dead or dying trees, SCN in the Atlantic forest depended primarily on cavities created by decay in live branches or trunks. Using cavities produced by natural decay releases SCNs from the depth constraints of excavated cavities. However, SCN did not avoid excavated cavities; rather, these often fell down before they could be reused. The functioning of nest webs in the Atlantic forest depends on the supply of large, live trees where wood decay forms deep, long-lasting cavities with small entrances, high above the ground.