3% or more of the diet were green hawthorne ( Craetaegus viridis - 7.3%), south- 

 ern smartweed ( Polygonum densiflorum - 4.3%), the seeds of buttonbush ( Cephalan - 

 thus occidentalis - 6.4%), a sedge ( Cyperus - 7.3%), and watergrass ( Hydrochloa 

 carolinensis - 5.8%). 



The food habits of another 63 ducks wintering in coastal South Carolina 

 were reported by Kerwin and Webb (1972). Again, these birds had fed largely on 

 plants (98.4%). Of the foods identified, pickerelweed ( Pontederia cordata - 

 13.1%) and northern jointed spikerush ( Eleocharis equisetoide s - 10.5%) were 

 the most important. Other species found in significant amounts were swamp 

 smartweed (6.1%), saltmarsh bulrush ( Scirpus robustus - 6.0%), dotted smartweed 

 ( Polygonum punctatum - 5.7%), wax-myrtle ( Myrica cerifera - 4.9%), arrowleaf 

 tearthumb ( Polygonum sagittatum - 4.8%), bigleaf tearthumb ( Polygonum ari- 

 f olium - 4.7%), softstem bulrush (4.0%), a flat sedge ( Cyperus odoratus - 3.6%), 

 and widgeongrass (3.1%). 



Landers et al. (1976) reported the foods eaten by 36 Black Ducks collected 

 during the hunting seasons in 1972-73 and 1973-74 from managed tidal impound- 

 ments. The majority of the food (93.8% vegetable) consisted of dotted smart- 

 weed (33.0%) and saltmarsh bulrush (34.1%). Only three other plants made up 

 more than 3% of the diet: saltmarsh cockspurgrass ( Echinocloa walteri - 8.4%), 

 redroot ( Lachnanthes caroliniana - 3.8%), and a flat sedge ( Cyperus polysta - 

 chos - 3.5%). 



Finally, Prevost et al. (1979) reported that six Black Ducks collected dur- 

 ing the 1976-77 hunting season in Georgetown County had fed almost entirely on 

 saltmarsh bulrush (89.7%) and widgeongrass (10.3%). 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying Black Ducks nesting at Pea Island, North Carolina, had a hatch- 

 ing peak in the first half of June, suggesting a peak of laying about a month 

 earlier (Palmer 1976a). In Maryland, a short distance farther north, peak lay- 

 ing occurred from mid- to late April. More northern populations nest later 

 (Bellrose 1976, Palmer 1976a), but terminate laying at about the same time. 



Mean Clutch Size Summarizing many studies that total more than 1,100 

 nests, Bellrose (1976) placed the average clutch size at 9.3 eggs; most clutches 

 contain between 7 and 11 eggs. 



Incubation Period The incubation period varies considerably depending on 

 ambient temperatures and the attentiveness of the hen. Averages in two studies 

 ranged from 23 to 29 days (Bellrose 1976). Extremes of 23-33 days are given by 

 Palmer (1976a), who noted that the mean incubation period was 26.2 days (mode 

 25) in Maryland, compared with a mean of 29.3 days (mode 27) for cooler Quebec. 



Hatching Success Overall, nest success of the Black Duck averages about 

 42%. About 6% of the eggs in successful nests failed to hatch in a Maryland 

 study (Bellrose 1976). Palmer (1976a) remarked that hatching success varies 

 from year to year throughout the range. He reported a range of hatching suc- 

 cess from 51.4% to 83.3% over a five-year period in Quebec. 



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