Date of Award
Doctor of Philosophy
Wood ducks are thought to depend on mature hardwood forests juxtaposed with palustrine wetlands but these habitats have been continuously degraded or destroyed since European settlement. Wood ducks are adaptable and the use of marginal habitats and nest boxes has extended their range and probably was important to the recovery of wood duck populations. Until now no study has analyzed the contribution of upland nesting to local population growth and maintenance. I investigated predation effects on nest site selection using wood duck nests and simulated nests placed in natural cavities. Using demographic data collected on wood ducks in southern Illinois, I created a population model to compare growth rates of population segments that nested in upland and floodplain habitats. During 1993-1998, 179 of 244 radiomarked hens remained on the study area as resident hens. One hundred-four nests were located by following radiomarked hens and 66% of nests were found in upland forests. Nests in the floodplain were initiated earlier than nests in the upland. Thirty-six percent of known nest cavities were used in subsequent years but <10% were used by the same hen. Nest success was greater in upland habitats (0.78 ± 0.10) than in floodplain habitats (0.54 ± 0.18). Hen survival through the nesting season was 0.80 ± 0.03 and did not differ between habitats or age classes. Sixty-five percent (n = 43) of simulated floodplain nests were destroyed compared to 33% (n = 45) in the upland. Logistic regression models of simulated nest data indicated cavity security could be important in the fragmented floodplain forests of Union County Conservation Area (UCCA). No physical characteristics of wood duck nest cavities differentiated successful and unsuccessful nesting attempts. The growth rate of the local population was positive and estimated to be about 3%. Lambda was most sensitive to upland nesting parameters and floodplain parameters appeared to have little impact on lambda. Hens nesting in the area appear to have adapted to predation pressure by nesting in more secure floodplain cavities at UCCA or by nesting in the upland habitats. Floodplain and upland habitats are ecologically intertwined and the local wood duck population would not survive if either habitat were destroyed or severely degraded.
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