Nest and Brood Attentiveness in Female Black Ducks

--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, 1.1 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 broodrearing 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. The behavior of female anatids during incubation and brood-rearing reflects the energetic demands of the reproductive season. High incubation constancy is typical of geese (Ryder 1970, MacInnes et al. 1974, Ankney and MacInnes 1978) and Common Eiders (Somateria mollissima; Korschgen 1977), which depend on stored nutrient reserves during this period. The females of smaller anatids are unable to store large endogenous reserves and, therefore, depend on environmental food resources to meet most of their metabolic requirements during incubation (Afton 1979). Because food is obtained during incubation recesses, recess duration and frequency may be related to metabolic reserves (Afton 1978), feeding efficiency (McKinney 1970), and density and availability of food resources. Incubation rhythms and brood attentiveness of female Black Ducks (Anas rubripes) have not been quantified. Mendall (1958:96) stated that "Black Ducks normally have only two rest periods per day, one in the early morning and another in late afternoon." He estimated the duration of incubation recesses at 60 min. Coulter and Miller (1968:20) concluded that "there was no period of the day when the majority of hens were off their nests." After hatching, female dabbling ducks usually remain with their broods until the ducklings are seven to eight weeks old (Munro 1949, Evans et al. 1952), although the duration of the hen-brood bond differs among species (Beard 1964, Ball et al. 1975). Before this time, hens leave their ducklings for periods ranging from 15-75 min (Beard 1964) to several hours or all day (Mendall 1958:126, Ball et al. 1975). We describe here the schedule of nest and brood attentiveness of radio-marked Black Ducks and relate the timing and duration of incubation recesses to weather and nest loca-