leatherleaf ( Chamaedaphne calyculata ) , sweetgale ( Myrica gale), and sedges 

 (Carex spp.) are common nest site habitats. Upland nests studied by Coulter 

 and Miller (1968) were found in nettles (Urtica dioica ) , raspberries (Rubus 

 spp.), and American yew ( Taxus canadensis ) . The variability of black duck 

 nest sites may prevent nest predators from forming an efficient search image 

 for locating nests (Reed 1974). Coulter and Miller (1968) reported that at 

 least a third of the female black ducks under observation produced a second 

 clutch of eggs when the first was destroyed. Some produced third clutches. 



A black duck clutch in Maine averages about 10 eggs (Coulter and Miller 1968). 

 They are generally laid at the rate of one per day. The weight of a clutch is 

 60% of the weight of the female bird, and the physiological stress of egg 

 production is associated with a weight loss of about 100 g during nesting, 

 including 50 g of fat (Reinecke 1977). The lipid energy reserves carried by 

 the female are a significant input into the energy requirement of the bird 

 during reproduction (Owen and Reinecke 1977). 



During egg-laying, the female usually visits the nest in the morning and 

 spends an increasing amount of time (2 to 10 hours) at the nest as the clutch 

 nears completion (Caldwell and Cornwell 1975). The female is rarely at the 

 nest at night until the clutch is complete. During egg-laying, the male rests 

 and preens when the female is in the nest, and joins her for feeding, bathing, 

 and preening when she is away from the nest. 



As the female increases her time at the nest, the bond between the pair 

 weakens. Soon after the female begins incubating the clutch, the male 

 abandons her, becomes less aggressive, and joins other groups of feeding and 

 resting males. The female assumes sole responsibility for hatching the eggs 

 and rearing the young. 



After abandoning the females, the males form flocks and move to larger marshes 

 and estuaries to molt their wing feathers and begin a period of 

 f lightlessness . The flightless period lasts about 4 weeks in May and June. 

 By early fall most adult males concentrate on intertidal flats along the 

 coast. 



During incubation the females remain on the nest except for one to four 

 (average of 2.3) rest periods of from 1 to 3 hours (average of 80 minutes) per 

 day (personal communication from J. K. Ringelman, School of Forest Resources, 

 University of Maine, Orono, ME.; June, 1978). Incubation of the clutch 

 requires 25 to 27 days. The egg-bound ducklings establish vocal contact with 

 the female and open (pip) the eggshells during the final 2 days of incubation. 

 The downy young remain in the nest until they are dry and the sheaths have 

 been rubbed from their down feathers. When they are dry and the weather 

 favorable, the female leads them to water. The average life span of females 

 is probably less than 2 years; Anderson (1975) reported mallards averaged only 

 1.7 years. This suggest most females produce only 1 or 2 broods per lifetime. 



The mortality rate of juvenile black ducks is high. Despite the 10 egg mean 

 clutch size (Coulter and Miller 1968), Spencer (1967) reported in an 18-year 

 study the average class III (6 weeks to fledging) brood size was only 5 for 

 the 560 broods observed. The range was 4.3 to 6.0 young per class III brood 

 (figure 15-12). 



15-44 



