BIOLOGY AND CONSERVATION OF THE COMMON MURRE 9 



predators and facilitate chick feeding in dense colonies. 

 Protection from predators also is afforded by adjacent 

 birds in the colony that attack nearby potential predators 

 of murre eggs and chicks (Birkhead 1977a, 1978b). 

 Immediately after hatch, chicks grasp fish by the head 

 end and swallow fish head first, avoiding injury from 

 fish spines (Oberholzer and Tschanz 1968). In the late 

 incubation and early chick-rearing periods, parent- 

 chick vocal recognition and chick breeding-site 

 recognition become strongly developed which 

 facilitates brooding, feeding, and chick return to the 

 site if dislodged (Tschanz 1968; Wehrlin 1977). 



On the South Farallon Islands, a murre chick spent 

 an average of 23-24 days at the breeding site before 

 departing from the colony with an adult (usually the 

 male) to complete its development at sea (see below; 

 Boekelheide et al. 1990). Chicks hatching later and 

 those at colonies at higher latitudes have shorter 

 chick-rearing periods (Boekelheide et al. 1990; Murphy 

 1995). Reduction in the time spent at the colony before 

 departure (i.e., chick departure from the colony when 

 only partly grown) could have evolved in relation to 

 decreased prey availability around the colony as the 

 breeding season progresses, increased predation on 

 later-hatched chicks, and reduced time remaining for 

 the parents to complete a prebasic molt before winter 

 (Birkhead and Harris 1985; Harris and Birkhead 1985; 

 Wanless and Harris 1988). Several other selective 

 pressures such as high wing loading, small prey 

 load-carrying capacity, chick provisioning rates of 

 breeding adults, chick growth rates on the colony and 

 at sea, and availability of prey resources far from the 

 colony also may have helped forge this life history 

 pattern (Stettenheim 1959; Sealy 1973; Gaston 1985; 

 Ydenberg 1989; Gaston and Jones 1998). 



Demography 



Adult and Subadult Survival 



The only long-term demographic study of the 

 common murre in the Pacific Ocean has been conducted 

 at the South Farallon Islands, California, where a banded 

 sample of murres has been studied since 1985 (Sydeman 

 1993). Murres from a large subcolony (n = 2.500 

 breeding pairs) had an annual survivorship of 94%, 

 whereas birds from a much smaller, new subcolony 

 (n = 50 breeding pairs) survived at a rate of only 77% . 

 This difference was attributed to high predation by 

 peregrine falcons in winter at the latter subcolony. 

 Annual survival rates for males and females were 99% 

 and 93%, respectively (Sydeman 1993). 



Studies on common murres in the Atlantic Ocean 

 provide demographic information that may be generally 



applicable to Pacific Ocean murres, despite significant 

 differences in prey resources, hunting of murres in certain 

 areas of the Atlantic, and various conservation issues. 

 Band returns at or away from the colony have been used 

 to determine adult and subadult survival rates in Europe 

 (Birkhead 1974; Mead 1974; Hudson 1985; Hatchwell 

 and Birkhead 1991). Adult annual survival rates of 

 common murres ranged from 87 to 94% in five European 

 studies. Survival rates of juveniles from the time of 

 colony departure to breeding age varied from 1 7 to 41 % 

 in 10 European studies, based mainly on band 

 recoveries. Many hatching-year juveniles die between 

 colony departure and during their first autumn 

 (Birkhead 1974; Stenzeletal. 1988; Bayer etal. 1991). 

 At the Isle of May, Scotland, survival of post-fledging 

 murres decreased with later hatching date in 2 of 6 years 

 studied (Harris et al. 1992). In this study, 12-47% of 

 chicks survived to at least six months of age, which 

 indicates that juvenile mortality also may be great in 

 mid- to late winter. 



Proportion of Adults that Breed 



Murres breed for the first time between the ages of 

 4-9, with most birds recruiting between ages 5 and 7 

 (Hudson 1985; Harris et al. 1994: Halley et al. 1995; W. 

 J. Sydeman, unpublished data). After reaching sexual 

 maturity, most murres lay eggs each year, unless unusual 

 circumstances occur. Harris and Wanless ( 1 995a) found 

 that 5-10% of adult murres did not breed each year, 

 owing mainly to mate loss. Sydeman (1993) noted that 

 banded adults did not breed in 4.5% of years studied at 

 the South Farallon Islands. During severe El Nino events 

 in 1982-83 and 1992-93, a large proportion of breeding 

 adults likely did not attend colonies or attended colonies 

 without laying eggs in California. Oregon, and 

 Washington (Boekelheide et al. 1 990: Carter et al. 2001 ). 

 Extensive colony disturbances by humans or predators 

 also might increase the proportion of adults that do not 

 breed, although some birds may delay breeding or move 

 to and breed at other colonies in response to such 

 problems (Parrish 1995; Carter et al. 2001). 



Hatching Success 



Mean "hatching success" (i.e., percentage of eggs 

 laid that hatch) for first eggs of Farallon murres from 

 1972 to 1983 was 85% (range, 80-93% in 1972-82), 

 but was much lower in 1983 (32%) because of severe El 

 Nino conditions (Table 1.1; Figure 1.5; Boekelheide et 

 al. 1 990). Replacement eggs had lower hatching success, 

 averaging 67% (range, 0-100% in 1972-82). Of 249 

 eggs (including first and replacement eggs) that failed 

 in 1972-83, 58% disappeared, 20% did not hatch (after 

 39 days of incubation), 8% rolled away from the site. 



