Condition Indices of Live-Trapped American Black Ducks and Mallards

Abstract

We compared condition indices of interacting American black ducks (Anas rubripes) and mallards (A. platyrhynchos) during staging to contrast changes in energy reserves that potentially influence survival or other population parameters. We live-trapped and banded 1,126 black ducks and 1,292 mallards from October through January during 1990-1993 on Ottawa National Wildlife Refuge (NWR) in Ohio, USA. Ducks were aged, sexed, and weighed; total body length, wing chord, culmen, and tarsus were measured to compute condition indices. The condition indices were used as dependent variables in multiple regression models to measure influences of annual date, species, and ambient temperature for each age-sex class. Adult male black ducks usually had slightly higher (1% to 3%) condition indices than adult male mallards. Initially, in 1990 and 1992, juvenile female mallards had 6% higher condition indices than juvenile female black ducks, but during these 2 years, black duck juvenile females improved condition at higher rates than their mallard counterparts. Temperature effects on condition of live-trapped birds were noted, especially during November 1991, when decreased body weights corresponded with frozen wetland foraging areas. Daily temperature similarly influenced black duck and mallard egress from the Lake Erie marshes. Species differences in breeding chronology and breeding ground productivity could influence the body condition of these birds and the observed seasonal trends. The poor body condition of juvenile black duck females observed during some years could possibly contribute to lower survival and reproductive performance during the following spring if these differences continue through the remainder of the winter.