Nesting wood ducks (A. sponsa) were studied for 7 yr (1973-1979) following placement of nest boxes within a 250 ha experimental greentree impoundment located at the Montezuma National Wildlife Refuge in central New York [USA]. Wood ducks filled available nesting space in the 3rd yr of the study. As nesting space became saturated, density strife was reflected in dump nesting, nest desertion and reduced hatchability. By the 5th yr of study, nesting interference had reduced nesting efficiency to 22%. Discontinued flooding of the impoundment during the last 2 yr of the study reduced the density of breeding pairs and restored nesting efficiency to 50 and 60%, respectively. Egg pecking by northern flickers (Colaptes auratus) increased as the study progressed and contributed to nest desertion. Dump nesting contributed efficiently to production under low density breeding conditions and permitted greater use of nest sites with a moderate but progressive decline in nesting efficiency as the population expanded. Total nest starts correlated negatively with nesting efficiency (r = - 0.75, P < 0.05) and positively with the number of dump nests (r = +0.96, P < 0.01), number of deserted dump nests (r = +0.77, P < 0.05), and number of ducklings left in nest boxes (r = +0.77, P < 0.05). Mark-recapture estimates of day-old duckling production showed a sharp increase in production from tree cavities from 1973 to 1974, a probable result of a rapidly expanding nesting population and removal of raccoons (Procyon lotor) from the study area.
