from Condor (an International Journal of Ornithology)
PhD DISSERTATION
ABSTRACT
This study investigates the relative roles of competition and predation in favoring shifts from nesting in tree cavities to nesting in alternative nesting niches by parrots (Aves: Psittaciformes) and trogons (Aves: Trogoniformes). Field investigations in pristine floodplain forest in the Peruvian Amazon show that termitarium nesting Brotogeris parakeets and Trogon melanurus partition the termitarium nesting niche, consistent with the prediction that predation favors nests spread throughout the available niche space. Phylogenetic analyses suggest that there have been multiple independent transitions from nesting in tree cavities to nesting in termitaria, cliffs, burrows and other substrates and that many species can use multiple substrates. Observations and nest box experiments indicate that natural tree cavities and nest boxes in the subcanopy are occupied at a rate of less than 2% suggesting that competition for tree cavities is not favoring the use of termitaria. Natural bird nests and artificial nests monitored indicate that predation rates on nests in old tree cavities are about 4 times higher than on nests in arboreal termitaria, suggesting that predation favors the use of termite mounds. Phylogenetically corrected analyses support the conclusions of the field investigations that transitions from nesting in tree cavities to nesting in novel substrates (termitaria, burrows, cliffs and others) results in reduced nest predation. These findings suggest that predation has molded avian nest site selection over evolutionary time. Based on the results presented here, an expansion of the predation/ diversity hypothesis is proposed. This revised theory may prove a useful tool in analyzing many well-known trends in avian ecology. In particular, this theory provides a new conceptual framework for examining questions about the relationship between the structural complexity of mature tropical forests and their extremely high avian diversity.