Incubation rhythms and brood attentiveness of radio-marked Black Ducks (Anas rubripes) were studied in southcentral Maine during 1977-1980. Recess duration and frequency differed between three females nesting near wetlands (x = 82 min, 2.3 recesses/day) and two nesting at upland sites(x = 183 min, I. I recesses/day), but incubation constancy was similar for all birds (x = 86.7%). A fourth wetland-nesting female apparently responded to the absence of down and concealing cover at the nest site by taking shorter and fewer recesses (x= 34 min, 1.0 recesses/day) than did other wetland-nesters with typical nests. Wetland-nesters took longer recesses with increasing air temperature and following long incubation sessions. After their ducklings were two weeks old, two brood-rearing females began leaving their broods to forage on nearby wetlands. Duration of rearing recess (x = 56 min) and total recess time (x = 94 min/day) were less during this mid-rearing stage than during the latter part of rearing (x = 265 min, 488 min/day). The two hen-brood bonds terminated at 43 and 48 days. We suggest that small endogenous nutrient reserves and the low density of invertebrate foods, typical of Black Duck breeding habitat, were critical factors affecting the evolution of Black Duck incubation behavior. Bouts of inattention during brood rearing may have also evolved in relation to food requirements; by foraging on wetlands away from their broods, females avoid competing with offspring for common food resources.