Autumn Roosting Flight Counts as an Index to Wood Duck Abundance

Roosts and roosting flights of wood ducks (Aix sponsa) were studied during autumn, 1959-64. Observations were made during 768 flight periods at 52 roosts. The primary study area was a 100-mile segment of Mississippi River bottoms in northeastern Iowa. Roosts were in many species of emergent vegetation. Barring major changes in habitat, autumn roost sites were usually the same each night and each year. Autumn migrants used roosts established in late summer by local birds. Seasonal changes in roosting populations were similar each year. September 20 is recommended for making roosting flight counts to be used as an index to annual changes in abundance of wood ducks. Evening counts were superior to morning counts. Numbers at a roost ranged up to 5,400. Sampling units, sampling schemes, sensitivity, and use of roosting flight counts for estimating abundance of wood ducks are discussed.