Sarcocystis in American black ducks wintering in New Jersey.

Macrocysts of a protozoan parasite, Sarcocystis sp., were found in 28 of 173 American black ducks (Anas rubripes) examined during winters 1984-1985, 1985-1986 and 1986-1987 in south coastal New Jersey (USA). No macrocysts were detected in 80 juvenile black ducks. In adults, the prevalence of macrocysts increased from 3% (1 of 37) in 1984-1985, to 36% (12 of 33) in 1985-1986, and 65% (15 of 23) in 1986-1987. This increase could result in a greater number of harvested birds being discarded, or a change in the attitudes of waterfowl hunters towards black ducks.