BIOLOGY AND CONSERVATION OF THE COMMON MURRE 1 3 



colonies in the last two decades (Parrish 1995; Carter et 

 al. 2001). 



In addition to the factors noted above, breeding 

 success probably increases with age, at least up to ages 

 6-9, as found in the thick-billed murre (Gaston et al. 

 1994). The size and density of murre colonies or breeding 

 groups also are known to affect the reproduction of 

 murres. At Skomer Island, Wales, breeding success was 

 higher in dense breeding groups than small scattered 

 groups because of high egg-laying synchrony and lower 

 exposure to gull predation (Birkhead 1977b, 1978b). 

 However, consistent negative relations between colony 

 size and chick growth rate, fledging weight, and 

 breeding success have been shown at the Pribilof 

 Islands, Alaska, possibly because of competition and 

 interference at breeding sites, and possibly competition 

 for prey (Hunt et al. 1986). Whereas resource depletion 

 around large seabird colonies has not been well 

 demonstrated (e.g., Birkhead and Furness 1985), 

 competition among foraging murres in dense 

 aggregations might contribute to decreased chick 

 growth, lower fledging weight, and possibly decreased 

 post-fledging survival (Gaston et al. 1983; Schneider 

 and Hunt 1984). 



At-sea Chick Rearing 



Flightless chicks leave the colony at about one 

 quarter adult mass, before attaining complete juvenile 

 plumage. Murre chicks are usually accompanied to sea 

 by a single adult (Figure 1 .6), rarely by two adults (Tuck 

 1961; Varoujean et al. 1979; Gaston and Nettleship 

 1 981; Harris etal. 1990; Scott 1990). Usually, only males 

 care for chicks at sea (Scott 1 973, 1 990; Birkhead 1 976b; 

 Harris and Birkhead 1985). Why male murres guard and 

 raise chicks at sea has not been well studied and remains 

 one of the more interesting questions in alcid biology. 



Figure 1.6. Parent-chick pair of common murres at sea just minutes 

 after departing from the colony at Three Arch Rocks, Oregon, 1 1 July 

 1989 (Photo by R.W.Lowe). 



Males are slightly larger than females on average 

 (Gaston and Jones 1998) but differential chick-guarding 

 or foraging abilities have not been demonstrated. 

 However, females collected during the early at-sea 

 rearing period exhibit low body weights, which may 

 indicate poorer condition by this time (Croll 1990; 

 H. R. Carter and S. G. Sealy, unpublished data). Females 

 occasionally may still accompany male-chick groups 

 (Harris et al. 1990). In 1969-73 near Yaquina Head, 

 Oregon, Scott (1990) found that chicks were 

 accompanied by a single adult (86.6%), two adults 

 (2.3%), one adult and another chick (less than 1%), or 

 were unaccompanied when observed (10.7%). Of 18 

 adult murres collected with chicks, 17 were male. In 

 Barkley Sound, British Columbia, in 1979-80, 32 single 

 adults that were accompanying chicks at sea were 

 collected and all adults were male, based on gonad 

 examination (H. R. Carter and S. G. Sealy, unpublished 

 data). In two instances, another adult or subadult was 

 strongly associated with the male-chick pair for a period 

 of time one was a female and the other a male (i.e., 

 possibly the female parent or both may have been 

 "helpers"). In 1995, USFWS personnel collected 10 

 adult murres that were accompanying chicks at sea off 

 Yaquina Head and all adults were male, based on gonad 

 examination (R. W. Lowe, unpublished data). 



When not feeding, chicks usually remain behind 

 but within 2 m of an accompanying adult. Adults feed 

 the chick for 1-2 months after fledging, although chicks 

 learn to dive and supplement parental feeding in the 

 latter part of the at-sea rearing period (Oberholzer and 

 Tschanz 1969; H. R. Carter and S. G. Sealy, unpublished 

 data). When adults dive for food, they usually surface 

 within 75 m of the chick. Adults and chicks 

 communicate frequently by loud calls to facilitate rapid 

 feeding, prevent separation, and reduce 

 kleptoparasitism or predation during feedings. 



Many dead chicks are washed up on beaches in the 

 late summer and fall (Stenzel et al. 1988; Bayer et al. 

 1991 ; Carter 1996). South of Alaska, the largest numbers 

 of dead chicks on beaches are found in Oregon, probably 

 reflecting the large breeding population (Carter et al. 

 2001), onshore winds, and many accessible beaches. 

 From June to September 1978-90, an annual average 

 of 421 (range, 33-1,236) dead hatching-year murres 

 were recorded on a 7.5-km long beach south of Newport 

 (Bayer et al. 1991). High mortality of hatching-year 

 murres also is sometimes recorded along the Washington 

 coast (U. W. Wilson, personal observation). On 

 5 September 1979, 39 dead murres were found floating 

 in Barkley Sound, British Columbia, after an intense 

 storm; 36 (92.3%) were dependent chicks (none had 

 yet achieved independence by this date), which suggests 



