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 suc cess, and use of cavities by other vertebrates at Muscatatuck National Wildlife Refuge (NWR), southcentral Indiana, in 1984-85. Of 789 surve yed tree cavities, 15% (122) were suitable for wood duck nesting. Mini mum 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 mat ure or sawlog trees (1.69 +/- 0.22 cavities/ha) than in areas with sma ller trees (0.31 +/- 0.11 cavity/ha). American beech (Fagus grandifoli a), red maple (Acer rubrum), and American sycamore (Platanus occidenta lis) produced 72% of suitable cavities, but composed only 28% of the b asal area. We estimated an annual survival probability of 0.91 for sui table cavities during the study. Cavities with vertically facing entra nces were used in greater proportion than other cavity types (P = 0.00 6). 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 w as 0.963 +/- 0.01 and estimated nest success was 0.22. Wood duck produ ction at Muscatatuck NWR was limited by raccoon predation and not by n est site availability.