Nest Parasitism on Constructed Islands in Northwestern North Dakota

Parasitism of duck nests can reduce host productivity. We examined effects of nest parasitism on success of host nests found on constructed islands in the Fuller-Big Meadows marsh in northwestern North Dakota from 1994 to 2000. We found 1642 duck nests of 10 species on 25 0.3-ha islands. Nine hundred- seventy (59%) of the 1642 nests were parasitized, of which 87% were parasitized by redheads (Aythya americana). The observed parasitism rate was greater than 50% in four of seven years and was highest in 1997 (81 %, n = 252). Mallard (Anas platyrhynchos) nests tended to have a higher probability of being parasitized than did nests of other species. The number of parasitic eggs laid per nest varied annually and was greatest in years with highest rates of parasitism (1997, 1999, and 2000). Among duck species, lesser scaup (Aythya affinis) nests contained the greatest number of parasitic eggs. From 1994 to 2000, nest success declined (97% Mayfield nest success in 1994 vs. 28% in 2000) whereas abandonment rates increased (2% in 1994 to 52% in 2000). Data revealed no evidence of a relationship between the probability of nest abandonment and incidence of parasitism