Factors influencing wood duck use of natural cavities

The lack of suitable cavities is a primary limiting resource for wood ducks (Aix sponsa). We studied wood duck nest site selection, nest success, and use of cavities by other vertebrates at Muscatatuck National Wildlife Refuge (NWR), southcentral Indiana, in 1984-85. Of 789 surveyed tree cavities, 15% (122) were suitable for wood duck nesting. Minimum nest densities were 0.13 ± 0.08 (SE) nest/ha in 1984 and 0.08 ± 0.03 in 1985; 7-9% of the suitable cavities were used by wood ducks. Density of suitable cavities was higher (P < 0.001) in areas with mature or sawlog trees (1.69 ± 0.22 cavities/ha) than in areas with smaller trees (0.31 ± O.11 cavity/ha). American beech (Fagus grandifolia), red maple (Acer rubrum), and American sycamore (Platanus occidentalis) produced 72% of suitable cavities, but composed only 28% of the basal area. We estimated an annual survival probability of 0.91 for suitable cavities during the study. Cavities with vertically facing entrances were used in greater proportion than other cavity types (P = 0.006). Cavity volume, entrance area, and diameter of the bole at entrance were important in distinguishing cavities used by wood ducks (n = 21), fox squirrels (Sciurus niger; n = 29), and raccoon (Procyon lotor; n = 22) in 1985. Distance to nearest water in early spring was greater for successful nests (P = 0.017) than for unsuccessful nests, probably because of raccoon foraging behavior. Daily survival rate for nests was 0.963 ± 0.01 and estimated nest success was 0.22. Wood duck production at Muscatatuck NWR was limited by raccoon predation and not by nest site availability