14 USGS/BRD/ITR-2000-0012 



greater susceptibility of chicks to inclement conditions 

 than adults (H. R. Carter and S. G. Sealy, unpublished 

 data). Overall, many of the deaths of first-year birds 

 compared to adults (see later) seem to occur before the 

 end of the at-sea chick-rearing period. 



Philopatry, Recruitment, and Intercolony 

 Movements 



Like all alcids studied to date, common murres show 

 a strong tendency to return to their natal colony to breed 

 (Hudson 1985). Once having bred, a murre normally 

 tends to return to the same or adjacent breeding site 

 each year (Birkhead 1977a; Harris and Wanless 1988; 

 Harris et al. 1 996b), and rarely moves to another colony. 



The process of recruitment is not well understood. 

 Studies in Scotland (Swann and Ramsey 1983; Halley 

 et al. 1995; Harris et al. 1996a) have shown that (1) 

 subadults (2-7 years old) visit several parts of their natal 

 colony before selecting a breeding site for their first 

 breeding, usually in the same subcolony but rarely close 

 to their natal site; (2) immatures tend to arrive 

 progressively earlier as they become older, and are 

 present more frequently; (3) immatures that previously 

 visited a colony are more likely to make future visits 

 and eventually breed at the colony site; and (4) younger 

 immatures (i.e., 2-3 years old) mostly attended "clubs" 

 on intertidal rocks. Over 2 years of study, 64-67% of 

 immatures visited their natal subcolony, and 57% of 

 murres breeding for the first time did so at their natal 

 subcolony. For six cohorts, an average of 42-54% of 

 chicks recruited within their natal group of 50-200 

 breeding pairs (Harris et al. 1996a). 



Little attention has been devoted to banding and 

 resighting or retrapping murres in the Pacific Ocean. 

 Intercolony movements have been documented at the 

 Isle of May, Scotland. During 1987-91, Halley and 

 Harris (1993) recorded 61 murres (2 adults and 59 

 immatures) on the Isle of May that had been banded 

 elsewhere. Only one or two of these birds actually bred 

 at the Isle of May, which suggests some inter-colony 

 visitation, but low natal dispersal. Habitat saturation or 

 loss, mate or site loss, colony increase or decrease, close 

 proximity of other colonies, or human disturbance may 

 lead to higher rates of emigration for common murres 

 (less than 30%) or Atlantic Puffins (Fratercula arctica; 

 less than 50%) at certain colonies (Harris and Wanless 

 1991; Lyngs 1993; Harris et al. 1996a). 



Colony Formation and Irregular Attendance 



Since adult murres exhibit high breeding-site 

 fidelity, high philopatry, and high annual survival rates, 

 adult and subadult murres tend to return to and attend 



natal colonies each year at traditional colony locations. 

 However, under certain circumstances, adult or subadult 

 murres will attend other locations with suitable breeding 

 habitats. Under favorable population conditions, murres 

 may attempt "colony formations" (i.e., the establishment 

 of colonies at "new" locations or the reestablishment or 

 "recolonization" of colonies at previously-used 

 locations). A primary hindrance to murre colony 

 formations seems to be social factors, especially the 

 initial process of attracting sufficient numbers of 

 conspecifics over a period of time to encourage breeding 

 attempts (i.e., pairing, copulation, and egg laying) at 

 locations with suitable breeding habitat (Buckley and 

 Buckley 1980). In addition, colony formations require 

 adequate prey resources plus relatively low levels of 

 human disturbance, interspecific interference, and 

 predation. 



Rarely have colony formations been documented 

 in the Pacific or Atlantic Oceans because of the 

 infrequency of this behavior and the difficulty of 

 detecting such events as they occur. With incomplete or 

 unavailable information on past breeding or lack of 

 breeding at specific colony sites, it is often impossible 

 to distinguish between the formation of new colonies 

 and recolonization events. Though the historical 

 information is incomplete, it seems that natural 

 recolonization events have occurred in northern 

 California and Oregon, but not in central or southern 

 California (Carter et al. 2001). 



Formation of colonies in northern California and 

 Oregon have been noted mainly within "colony 

 complexes" (Carter et al . 200 1 ) where murres apparently 

 expanded from long-used colony sites or subcolonies 

 to breed on nearby (i.e., within a few kilometers) 

 unoccupied breeding habitats. Many fewer examples 

 of colony formation away from nearby existing colonies 

 are known. However, apparent recolonizations in 

 Mendocino County, California, and intermittent 

 formation of small colonies on the west coast of 

 Vancouver Island, British Columbia, occurred long 

 distances away from existing colonies. 



Murre colony formations in California and Oregon 

 often have been associated with nesting Brandt's 

 cormorants. In fact, murres often breed in association 

 with nesting Brandt's cormorants in California, Oregon, 

 and Washington (e.g., Sowls et al. 1980; Speich and 

 Wahl 1989; Boekelheide et al. 1990; Carter et al. 1992). 

 Cormorants may facilitate murre colony formations by 

 providing added protection to murres from potential 

 gull and corvid predation, as well as providing stimuli 

 for murre breeding (McChesney et al. 1998, 1999; 

 Sydeman et al. 1998; Carter et al. 2001). 



