|Abstract or Summary
- In 1976 and 1977 I examined three broad problems associated with the recruitment of young mallards, Anas platyrhynchos, in the Prairie Pothole Region of North Dakota. The three problems studied were: the effects of interspecific nest parasitism on production; the chronology and magnitude of total-brood loss during the brood-rearing period; and, mobility, home range, and habitat utilization of broods. Nest parasitism occurred only in mallard nests that were in marsh habitat. Of 24 active mallard nests located in marsh habitat during 1976, 46% were parasitized. Forty-two percent were parasitized by redheads, Aythya americana, and 8% by ruddy ducks, Oxyura jamaicensis. Only three mallard nests were found in marsh habitat in 1977, presumably because of a severe drought, and none were parasitized. Nest parasitism by redheads or ruddy ducks did not significantly decrease mallard nest success (P>0.05). Parasitism by redheads reduced mallard clutch-size by about 1.5 eggs; parasitism by ruddy ducks had no significant effect on mallard clutch-size. In successful nests, nest parasitism by redheads significantly reduced mallard egg success (P<0.05), primarily through host egg displacement. Due to a small sample size, the effect nest parasitism by. ruddy ducks had on mallard egg success was not determined. Nest parasitism by redheads could potentially reduce the number of mallards produced in the Prairie Pothole Region during some years. Survival of mallard broods was estimated from data obtained from 25 radio-marked broods monitored during 1976 and 1977. Radio-equipped mallard hens fledged at least one duckling in 44% of broods initially hatched in 1976 and 55% in 1977. Combined brood survival for 1976 and 1977 was 48%. Eighty-five percent of the loss of entire broods occurred within the first two weeks after hatching and all losses occurred in wetlands. Few ducklings and no broods were lost during overland travel. The primary predators on ducklings in wetlands were mink, Mustela vison. Mallard broods were quite mobile during the first few weeks after hatching, but mobility varied greatly between 1976 and 1977. Of 16 broods monitored in 1976, 12 made major overland moves among wetlands and utilized from 2 to 10 different wetlands during the brood-rearing period. In 1977 only 2 of 9 radio-marked broods made major habitat shifts. The reason for the difference in brood mobility between 1976 and 1977 appeared to be related to drought conditions. The area of the corrected 'home range of radio-marked broods increased rapidly until broods were about one week old; by two weeks the home range of most broods was stable. Cumulative home ranges varied among broods but averaged 11.0±4.7 ha (mean±SD). Broods used only a small portion of the home range in any one week period. Generally, the home range of a brood on a particular wetland ranged in size from 4 to 6 ha. Habitats utilized by broods varied greatly between 1976 and 1977. In 1976, when many types of wetlands contained water, mallard hens with broods demonstrated a significant preference for whitetop ponds, but rejection was indicated for other types of seasonal wetlands. In 1976 overall use of semipermanent wetlands was significantly less than expected; but in 1977, when drought conditions prevailed on the study area, semipermanent wetlands were used by mallard broods directly in proportion to their availability. Mallard hens with broods used brood-rearing areas with high standing crops of benthic invertebrates.