DEMOGRAPHY AND POPULATIONS 



MEASURES OF BREEDING ACTIVITY 



Age at first breeding; intervals between breeding. Only a single known-aged male has 

 been seen with a mate; it was marked as a juvenile in 1992 on Mineral Creek, Montana, and 

 observed by J. Ashley paired with a female (white NH) at Hornby Island, BC, in March 1 996. 

 Adult male breeding plumage is attained at three years of age (Phillips 1925). No one- or two- 

 year-old males, out of 176 independent male observations, have been observed in Montana 

 during 1992-95 surveys (this report, Ashley pers. comm.). Very few, if any, 1 or 2-year-old 

 males have been reported on the breeding grounds in North America. Yearling males make up 1- 

 2% of the population on the breeding grounds in Iceland (Bengtson 1972, Gardarsson 1979). 



The youngest female known to have bred is a 2-year-old which raised a brood of 3 in 

 1994 on Trail Creek, Montana; nine additional non-breeding (or not successfully breeding) 2- 

 year-olds have been observed on natal streams and 16 marked 2-year-olds are known to have 

 been alive. Additionally, only a single 3-year-old has bred successfully (on Marten Creek in 

 1995); 7 additional non-breeding 3-year-olds have been observed on natal streams, and 1 1 

 marked 3-year-olds are known to have been alive. Ages of females when first seen on the 

 breeding grounds have included 2-year-olds (10) and 3-year-olds (4); females seen on the 

 wintering grounds, that had not been seen on the breeding grounds, included 1 -year-olds (2) and 

 3-year-olds (3). Since we began marking juveniles in 1992, the oldest known-age birds in 1995 

 were 3-year-olds. In Iceland, Bengtson (1966) believed that 2-year-old females Harlequins did 

 not regularly go to the breeding grounds; this was opinion, and not based on known-age birds. 



Some females on breeding streams apparently, however, do not lay eggs (Bengtson and 

 Ulfstrand 1971, Dzinbal 1982, Wallen 1987, Cassirer and Groves 1991). Bengtson and Ulfstrand 

 (1971) classified 15-30% (n=48) of adult (by bursae inspection) females as non-breeders, and 

 found that 87% of all clutches were successful; therefore, approximately 90% of non-breeding 

 females did not even attempt to breed in Iceland. Additionally, examination of ovaries of 6 non- 

 breeding females showed that none had lain eggs (Bengtson and Ulfstrand 1971). Many of these 

 non-breeding "adults" may have been young (2-3 year-old) birds, since cloacal examination gives 

 adult status to 2-year-olds. Dzinbal (1982) estimated that 53-95% of females not producing 

 broods did not attempt to breed; those results may have been due to use of patagial markers 

 negatively affecting breeding behavior (Bustnes and Erikstad 1990). Wallen (1987) reported that 

 some females left the breeding stream at the same time as their mates; unpaired females arrived 

 about 4 weeks later than pairs, did not breed, and left after 3-5 weeks. 



Clutch size. Twelve clutches from the Pacific Northwest averaged 6.25 eggs (range 3-7) 

 and are listed below. In Montana, a clutch of 5 was reported (Diamond and Finnegan 1993), four 

 clutches of 6, 6, 7, and 7 were reported in British Columbia (Campbell et al. 1990), and 2 

 clutches of 7 were reported in Washington (Jewett et al. 1953). Cassirer et al. (1993) reported 3 

 nests with 3, 5, and 7 eggs in Idaho. Thompson et al. (1993) reported 2 nests, each with 7 eggs, 

 in Oregon, while Gabrielson and Jewett (1940) reported a clutch of 6 eggs on 30 May 1931 on 

 the Salmon River near Zigzag. In Iceland, 77 complete clutches averaged 5.7 eggs with a range 

 of 3-9 (Bengtson 1972). There was a seasonal decline in clutch size (Bengtson 1972). The mean 

 number of eggs to hatch from successfiil nests was 5.3 (Bengtson 1972). A single known 

 Greenland clutch was 8 (Salomonsen 1950). 



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