Individual broods in North America range from 3 to 13 young, with an average of 

 7.8 (Bellrose 1976). 



Fledging Success Broods of young often combine into large groups (Bellrose 

 1976, Palmer 1976b), masking the success of individual broods. 



Age at Fledging The age at first flight for birds in the wild is not known, 

 but is probably less than the 65 days or more required by the Common Merganser 

 (Bellrose 1976). Heinroth and Heinroth (1928 jji Palmer 1976b) estimated an age 

 at first flight of 59 days; their estimate was based on observations of captive 

 birds. Cramp et al. (1977) indicated that young achieved independence before 

 this, at about 50 days. 



Age at First Breeding Red-breasted Mergansers first breed as they approach 

 two years of age (Palmer 1976b). 



Mortality of Eggs and Young Kortegaard (1968) indicated that nests in 

 North Jutland had been destroyed by otters ( Lutra lutra ) , rats (Rattus norveg- 

 icus ) , foxes ( Vulpes vulpes ) , and gulls ( Larus sp.). 



Renesting Bellrose (1976) suggested that renesting is rare because of the 

 lateness of nest initiation, but Palmer (1976b) cited data to suggest it happens 

 frequently in Europe. 



Maximum Natural Longevity The oldest bird yet recorded in North America 

 was about 5 years old (Clapp et al . in press), but records from Europe show that 

 Red-breasted Mergansers may attain an age of 9 years, 8 months (Rydzewski 1978). 



Weight Nelson and Martin (1953) gave a mean weight of 18 adult males of 

 2.5 lb (1,100 g) and that of 17 adult females of 2.0 lb (910 g) . 



SUSCEPTIBILITY TO OIL POLLUTION 



Its wintering habitat in coastal marine habitats and its method of feeding 

 (diving, often in flocks) make the Red-breasted Merganser vulnerable to oiling. 

 There are many recent reports of oiled birds, both from the Old and New Worlds 

 (Table 13), but few major losses have been reported. Ranwell and Hewitt ( in 

 Vermeer and Vermeer 1974) indicated heavy losses following a spill in Poole 

 Harbour, England. Brown et al. (1973) suggested that as much as two-thirds of 

 the Red-breasted Mergansers wintering in Chedabucto Bay, Nova Scotia, died fol- 

 lowing an oil spill in February 1970. Mortality from oiling has also been re- 

 corded in the southeastern United States. Robertson and Mason (1965) found two 

 Red-breasted Mergansers that had been killed by oil at Long Key in the Dry Tor- 

 tugas in January 1964, and at least two more died from oiling following a spill 

 off Tampa, Florida, in January 1970 (data from the Bird-Banding Office). 



King and Sanger (1979) gave the Red-breasted Merganser an Oil Vulnerability 

 Index of 56 (out of a possible 100) for birds in the northeast Pacific. This 

 figure indicated a species that might be affected, but not catastrophically so. 



A substantial proportion of the American Red-breasted Merganser population 



430 



