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Nesting ecology and community structure of cavity-nesting birds in the Neotropical Atlantic forest Cockle, Kristina


Tree cavities are proposed to limit populations and structure communities of cavity-nesting birds, making these birds particularly vulnerable to anthropogenic activities that destroy potential nest trees. The greatest diversity of cavity-nesting birds is found in tropical rainforests, yet little is known about the ecology or conservation of these birds. I studied how the production, consumption and loss of tree cavities structure a cavity-nesting community in one of the five most important global biodiversity hotspots, the subtropical Atlantic forest of Argentina. I found that the cavity-nesting community in the Atlantic forest is structured primarily around the production and persistence of high, deep, non-excavated cavities in large live trees. I show the first experimental evidence that the supply of tree cavities limits the breeding density of secondary cavity-nesting birds (species that do not excavate their own cavity) in a tropical forest. Conventional tropical logging strongly reduced cavity availability: logged forest had half the basal area of primary forest, but only one third the density of large trees, nine times fewer cavities suitable for nesting birds, and 17 times fewer active nests. My results suggest a severe impact of tropical logging on the abundance of cavity-nesting birds, and a need for management strategies that conserve large live cavity-bearing trees. In contrast to North America where vertebrate excavators create most of the nest cavities for secondary cavity nesters, but similar to sites outside of North America, 80% of nests of secondary cavity nesters in the Atlantic forest were in cavities created by natural decay processes. These non-excavated cavities were often in live stems or branches. The predominance of excavated cavities in North America and non-excavated cavities elsewhere can be explained partly by high rates of persistence of excavated cavities at a site in North America and low rates of persistence of excavated cavities at a site in Europe and my site in Argentina. To conserve cavity-nesting birds of the Atlantic forest, I recommend a combination of policies, economic assistance, environmental education, and technical support for forest managers and small-scale farmers, to maintain large healthy and unhealthy trees in commercial logging operations and on farms.

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