16 USGS/BRD/ITR-2000-0012 



Most egg and chick predation in Farallon colonies 

 was attributed to "specialist" western gulls that nest in 

 or adjacent to breeding groups of murres (Spear 1993). 

 These gulls tend to expel other gulls from their territories 

 and, consequently, gull predation does not necessarily 

 increase where large numbers of gulls nest near murres, 

 except during breeding failures and abandonments when 

 egg loss would likely occur regardless of gull predators. 

 Murre-specialist western gulls may not be present at 

 small murre colonies (L. B. Spear, personal 

 communication). 



Foraging Ecology 



Common murres forage widely between coastlines 

 and outer parts of the continental shelf, but are most 

 common in inshore waters (Brown 1980; Bradstreet and 

 Brown 1985; Briggs et al. 1987). During the breeding 

 season, foraging by breeding birds and older subadults 

 attending colonies becomes restricted to within foraging 

 distance of colonies, but birds still can forage as far as 

 200 km away from colonies (Cairns et al. 1990). In 

 central California, murres tend to forage largely within 

 about 35 km of breeding colonies (Briggs et al. 1987, 

 1988; Ainley et al. 1990, 1993; Allen 1994). However, 

 younger subadults or adults not attending colonies can 

 be found farther from colonies during the breeding 

 season. In winter, murres tend to forage farther from 

 colonies, often at distances that prevent regular colony 

 attendance. However, winter attendance by birds at 

 certain colonies reflects foraging within a short distance 

 from the colony. 



Feeding areas, both far from and near shore, are 

 predictable to some degree since recent studies strongly 

 link murre at-sea densities to specific oceanographic 

 features (Brown 1980; Woodby 1984; Schneider et al. 

 1990). For instance, ocean flow gradients are generated 

 from coastline and bathymetric features (Casanady 

 1982; Allen etal. 1983; Schneider etal. 1990) and lead 

 to prey aggregations at "fronts" between water types. 

 Smaller fronts in nearshore waters can be related to local 

 topographic features, tides, and river plumes. However, 

 many factors contribute to prey abundance, distribution, 

 and availability at fronts or other locations, such as 

 locations of spawning areas and habitats of fish prey, 

 patterns and timing of marine productivity in specific 

 coastal areas, distance from colonies, and various effects 

 of human activity (e.g., fisheries, pollutants, and 

 freshwater outflow from rivers). Because of their ability 

 to dive to great depths (up to about 180 m; Piatt and 

 Nettleship 1985), murres have wide access to prey 

 throughout a large portion of the water column and can 

 forage along the bottom in many nearshore areas. 

 However, common murres often forage at midwater 



depths, perhaps because of prey abundance, vertical 

 distribution of prey during daylight hours, underwater 

 energy expenditure, foraging efficiency, or differing 

 caloric value of prey (Spring 1971; Bradstreet and 

 Brown 1985; Birkhead and Nettleship 1987c; Ainley 

 etal. 1996). 



Foraging patterns of breeding murres have been 

 studied mainly by observing adults feeding chicks at 

 colonies. To feed chicks, adults typically capture single 

 prey items (usually 4-15 cm fish, but occasionally squid 

 and invertebrates) in at-sea foraging areas and fly back 

 to the breeding site, carrying the fish lengthwise in the 

 bill. As the chick grows larger, feeding rates and size of 

 fish may increase or remain the same (Burger and Piatt 

 1990; Hatchwell 1991; Harris and Wanless 1995b). 

 Chick feeding rates are largely unaffected by weather, 

 sea conditions, or chick age but high winds and heavy 

 seas can affect adult foraging behavior (i.e., increase 

 foraging time and effort) and reduce the size of fish fed 

 to chicks (Birkhead 1976a; Slater 1980; Burger and 

 Piatt 1990; Finney et al. 1999). 



The response of breeding murres to prey availability 

 was studied in the Shetland Islands, Scotland, during 

 years of high and low prey abundance (Uttley et al. 

 1994). In both years, murres fed on lesser sand lance 

 (Ammodytes tnarinus). Between years, hatching success 

 was similar, but the rate of chick feeding, chick growth, 

 fledging weight, and fledging success were all higher 

 in the year when prey were most abundant. Chick 

 feeding frequency showed little variation during the 

 early chick-rearing period at the colony when prey were 

 more abundant, but increased as the breeding season 

 progressed and prey were less abundant. When prey 

 abundance was low, adults spent less time at the colony 

 and their foraging trips required more than twice as 

 much time. Murre feeding also was studied concurrently 

 by using radio telemetry (Monaghan et al. 1994). Low 

 prey abundance had a dramatic impact on foraging 

 patterns ( 1 ) feeding trips were longer, (2) birds foraged 

 more than six times farther from breeding sites, (3) birds 

 spent more than five times as much time diving, and 

 (4) their estimated energy expenditure was twice as 

 great. Longer foraging time reduced time at the colony 

 tending the chick. These changes in time allocation 

 and energy expenditure could adversely affect chick 

 survival at the colony and possibly adult survival after 

 breeding. However, murres may compensate for such 

 changes. Zador and Piatt (1999) found little difference 

 between chick feeding rates, chick growth rates, or 

 breeding success between increasing and declining 

 colonies (with higher and lower prey availability, 

 respectively) in Cook Inlet, Alaska, but time spent on 

 the colony was greater at the increasing colony. 



