6 USGS/BRD/ITR-2000-0012 



season. Like many other seabirds, murres live entirely 

 at sea, except for breeding-related activities at the 

 colony, which include breeding-site prospecting and 

 defense; courtship, pairing, and copulation; egg laying 

 and incubation; and chick rearing. 



During the breeding season, breeding adults (i.e., 

 after reaching sexual maturity and breeding for the first 

 time) obtain a mate and breeding site, lay and incubate 

 eggs, and brood and feed chicks at the colony. However, 

 during severe El Nino-Southern Oscillation (hereafter 

 "El Nino") conditions, or in response to other factors 

 (e.g., human disturbance or severe disruption by 

 predators), many or all murres may abandon colonies 

 before or after egg laying. 



During incubation, steady numbers of birds attend 

 breeding sites although some daily variation occurs 

 (Boekelheide et al. 1990; Takekawa et al. 1990). At 

 Triangle Island, British Columbia, murre numbers 

 peaked in early evening with another lower peak in the 

 early morning during the incubation period (Rodway 

 1 990). Lowest numbers occurred around mid-day ( 1 300- 

 1 600 h PDT). The number of murres attending colonies 

 may decline after the median hatching date if parents 

 spend more time away from the colony foraging for 

 chicks. Numbers attending colonies drop sharply as 

 chicks leave the colony (Boekelheide et al. 1990). This 

 general pattern of attendance during the breeding 

 season also has been observed at eastern Canadian and 

 Alaskan colonies (Tuck 1961 ; Piatt and McLagan 1987; 

 Hatch and Hatch 1989). 



At some colonies, nonbreeding subadult murres (2- 

 6 years old) congregate on land in "clubs" adjacent to 

 breeding areas (Birkhead and Hudson 1977). Attendance 

 patterns vary more at clubs than breeding areas, both 

 within and between years, and clubs may not be present 

 at certain colonies. Virtually nothing is known about 

 colony attendance patterns of nonbreeding murres (i.e., 

 subadults and nonbreeding adults) along the west coast 

 of the United States and British Columbia. 



At the end of the colony chick-rearing period, 

 successful breeding males and their partly-grown chicks 

 depart the colony. During the at-sea chick-rearing period, 

 chicks are fed at sea until independence. Other adults 

 (i.e., females, failed breeders, and subadults) also cease 

 colony attendance once male-chick pairs have departed. 

 However, female adults may linger at breeding sites for 

 some time, probably to defend the breeding site against 

 prospecting birds if present (Birkhead and Nettleship 

 1987a). Adults and subadults undergo a flightless, 

 prebasic molt at sea within 1-2 months of leaving the 

 colony and develop a "mottled" or white head plumage 



(Birkhead and Taylor 1977). Younger subadults molt 

 earlier than older birds in captivity and the wild 

 (Swennen 1977; H. R. Carter and S. G. Sealy, unpublished 

 data). No colony attendance occurs during the at-sea 

 chick rearing period, although sporadic attendance of 

 breeding sites by birds that are not feeding chicks can 

 occur at the South Farallon Islands for a short period 

 after the colony has been largely evacuated. 



In the nonbreeding season, adults and possibly 

 subadults may resume colony attendance and perform 

 breeding-related behaviors such as site or pair-bond 

 maintenance, or prospecting (Harris and Wanless 1988, 

 1989, 1990a,b). The degree of colony attendance in the 

 nonbreeding season varies between geographic areas. 

 No attendance occurs when murres move to wintering 

 areas that are disjunct from colonies. A partial 

 prealternate molt occurs in late fall and winter when 

 adults and subadults redevelop black head plumage, 

 although molt in adults and older subadults precedes 

 younger subadults (Swennen 1977). Almost all murres 

 attending the South Farallon Islands in December- 

 March have black heads but a few have mottled heads 

 (Smail et al. 1972). Thus, few or no younger subadults 

 visit the colony during winter and stay at sea. 



In winter, California colonies are visited 

 periodically by varying numbers of birds, starting as 

 early, as October and extending through the winter 

 (Ainley 1976; Sowls et al. 1980; DeGange and Sowls 

 1981; Boekelheide etal. 1990; Parker etal. 1997, 1998; 

 Hastings et al. 1998; Carter et al. 2001). At the South 

 Farallon Islands, much variation in winter attendance 

 occurs between years because of local prey availability, 

 weather conditions, and behavioral factors related to 

 breeding-site attendance (Boekelheide et al. 1990; H. 

 R. Carter, unpublished data). Fairly regular attendance 

 begins as early as February but murres do not stay 

 overnight at breeding sites until April, shortly before 

 egg laying. In Oregon, murres sometimes attend 

 colonies as early as mid-December (Bayer and Ferris 

 1988), but regular attendance does not occur until 

 March-April. No information is available about winter 

 colony attendance in Washington and British Columbia 

 where it may not occur regularly. Murres started 

 attending the Tatoosh Island colony area in March- 

 April (Parrish 1995). 



In winter, murres often raft in waters around the 

 South Farallon Islands before landing on the colony 

 and, at times, rafting occurs without subsequent 

 landings. Similar behavior also has been noted at 

 nearshore colonies in central California (M. W. Parker, 

 unpublished data). In spring, murres often raft in 

 association with frequent landings on and evacuations 



