areas may be found in Johnsgard (1975), Bellrose (1976), and Palmer (1976b). 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying Nesting in Iowa and Manitoba began in May with peaks in early 

 (Iowa) or late (Manitoba) June (Low 1941, Bellrose 1976, Siegfried 1976a). 

 Palmer (1976b) noted complete first clutches by late April or early May, while 

 those nesting in the northern tier of states complete clutches from the end of 

 May into June. In some areas of the United States some eggs may be laid as late 

 as mid-July. Eggs have been found in the West Indies from December to May, with 

 a peak in March; birds in South America evidently lay from about November to 

 April (Palmer 1976b). 



According to Palmer (1976b), Ruddy Ducks are single-brooded in the north- 

 ern portion of their breeding range; he suggests that they may often be double- 

 brooded in the southwestern United States and perhaps in Mexico. 



Mean Clutch Size Siegfried (1976a) reported that most nests studied in 

 Manitoba contained seven or eight eggs; the mean was about 7.5 eggs. Summar- 

 izing several studies, Bellrose (1976) calculated an overall average clutch of 

 8.05 eggs. The normal range of clutch size is apparently 5-15 eggs (Bellrose 

 1976, Palmer 1976b). Ruddy Ducks also have "dump nests" in which more than one 

 female may lay eggs. As many as 80 eggs have been found in a single nest (Pal- 

 mer 1976b). 



Incubation Period The incubation period at 6 nests in Iowa was 25 or 26 

 days (Low 1941); that in 7 nests in Manitoba was 23 days (Hays in Bellrose 1976). 



Hatching Success Bellrose (1976) summarized studies of 356 nests of which 

 69.6% were successful in having some young hatch; the average successful nest 

 produced 5.7 ducklings. Palmer (1976b) mentioned 3 studies in which the hatch- 

 ing success in nests in which at least some young hatched ranged from 70.4% to 

 100%. Low (1941) noted that some females lead the young from the nest before 

 all the eggs hatch; the abandoned eggs may be the latest laid eggs or eggs 

 dumped by other females (Bellrose 1976). 



Fledging Success Bellrose (1976) reported a considerable loss in ducklings 

 during development, so that broods nearing fledging averaged only 4.4 young. 



Age at Fledging Young Ruddy Ducks could fly at an age of of six or seven 

 weeks in Manitoba (Hays in Bellrose 1976). Palmer (1976b) indicated that age at 

 first flight in wild birds was about six weeks. 



Age at First Breeding Palmer (1976b) pointed out that there is no definite 

 information on age at first breeding for wild Ruddy Ducks. Bellrose (1976) sug- 

 gested that some, but not all, Ruddy Ducks begin breeding in the first year but 

 noted instances in which captive birds did not breed until the second or third 

 year. 



Mortality of Eggs and Young Low (1941) reported the mink ( Mustella vison ) 

 as a predator on Ruddy Duck nests. Some eggs are deserted as a result of nest 



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