Density, distribution, and attributes of tree cavities in an old-growth tropical rain forest

Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.