Common Murre Uria aalge Scientific name definitions
Version: 2.0 — Published August 6, 2021
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Habitat in Breeding Range
Breeds on cliff ledges, sloping island surfaces, or flat areas on rocky headlands and islands in which birds have a view of the ocean (see Breeding). When not at breeding sites during breeding season, frequents continental shelf and slope waters, rarely to beach (87, 111, 112, 113). In nonbreeding season, however, often found close to shore, on occasion far up inlets and sounds.
During breeding, most commonly found where prey concentrated by oceanographic fronts, tidal sheers, and the like, within flight range of colonies (e.g., 114, 115). At large scale, associated with waters exhibiting steep temperature gradients (4–5°C/100 km) and low visibility (9–10 m) owing to phytoplankton production (116). At mesoscale, along upwelling plumes and fronts, occurs on warm side, avoiding recently upwelled water, which generally lack prey (117, 84, 118); as studied off Oregon, associated especially with long-shore upwelling front, exhibiting temperature gradients of 1°C/3 km, affected as well by depth and salinity (115). Also associated with shelf-break front (119) and density fronts associated with runoff plumes, e.g., Puget Sound (Washington), Columbia River (Oregon/Washington), San Francisco Bay (California; 120, 118). A logistic model considering habitat factors over entire expanse of central California shelf, slope, and off-shelf waters (to 3,000 m deep) indicated preference for areas shallower than shelf break, with cooler water having a shallow thermocline (121); in another model, using a more spatially and temporally expansive data set, 58% of density variation explained by sea-surface temperature (cooler), thermocline strength (more stratified), distance from continental shelf break (curvilinear), distance from land (closer), and distance from breeding colonies (closer; 119). At smallest scales (kilometers), such as nearshore of Monterey Bay, California, little correlation between occurrence and ocean properties (122).
During El Niño, with upwelling of cold water not evident and food sparse, feeds closer to shore, i.e., in waters < 30 m deep (111, 102). Noted then in larger numbers within coastal estuaries such as San Francisco and Yaquina Bays (California; 123, 111) and, perhaps even eastern Puget Sound (Washington; 124). On longer time scale, as waters of California Current warmed slightly during 1985–1996, murres moved farther inshore from shelf break (119).
In Gulf of Alaska, at large scale, found on colder side of Subarctic Front, especially over neritic waters (113). Accordingly, occurrence inversely related to water depth, distance from land, sea-surface temperature, and salinity; found in bays but less so in those associated with estuaries, except during winter when common in inlets and fjords (125, 126, 127, 128, 129). Neritic occurrence confirmed by stable isotope analysis (130).
In Bering Sea, associated with midshelf front, where isothermic inshore waters meet stratified offshore waters (80), as well as shelf-break front (131) and tidal fronts generated by rapid flow of water over bathymetric features (132, 133, 134). Nearshore, also frequents density fronts associated with Alaska Coastal Current (135, 136, 137). Where both Uria species occur, Common Murre found in shallower water than Thick-billed Murre (131, 138, 139). In Chukchi Sea, it is also associated with warmer Alaska Coastal Current, moving north and east through Bering Strait, rather than occurring offshore in Bering/Anadyr Water; pattern related to forage-fish abundance (arctic cod [Boreogadus saida]; see below; 140, 139). Off Newfoundland, similarly associated with fronts and other ocean features that concentrate prey, especially those associated with topographically induced flow gradients (141). Foraging habitat shifts seasonally, at first inshore (bays), but then, when capelin (Mallotus villosus) present, to waters overlying ledges farther offshore (142).
At smallest spatial scales (≤ 2–3 km), particularly large flocks associated directly with prey schools, but small flocks may or may not be so associated (138, 143, 142, 144). It’s not just other murres with which individuals compete; for instance, a negative relationship exists in California Current between murre and salmon density, the salmon being a competitor (115). Numbers in flocks of 6–12 birds usually proportional to fish biomass underneath (144). A threshold of school size exists (e.g., schools of fish > 15 g/m2 in density varying by prey species), below which Common Murre may not be interested, related to high energetic requirements (145, 140; see below). Suitable prey school size/density, as judged for capelin, increases as the overall abundance of capelin increases at the regional scale (146).
Subadults frequent general area of breeding colonies, within 40 km, regardless of whether they visit breeding ledges (84). In Gulf of Farallones, California, subadults concentrate in southern portion (Half Moon Bay), where breeders and nonbreeders concentrate during winter (abundant food), about 40–60 km from major colonies in central California (112, DGA).
Habitat in Nonbreeding Range
Sea-ice cover, less so prey availability, severely limits distribution during winter at high latitudes (79, 88, 80). Occurs only in extreme southern portion of Bering Sea; western Alaska breeders apparently winter in southern Bristol Bay, among Aleutian Islands, and over shelf of southeastern Alaska (147, 148). Males and females may winter in different areas, returning to same ones each year (149). Elsewhere, breeding and winter range correspond in accord with seasonality of ocean fronts (see Breeding Range in Distribution). Spread thinly and no longer associated with breeding sites through December; begin to concentrate near breeding sites January–March (84, 27).
Oregon and Washington breeders rear chicks, undergo Prebasic molt, and partly winter among sheltered bays and straits to the north, where few breeding colonies exist, e.g., Straits of Juan de Fuca and Georgia and west coast of Vancouver Island, often to feed on herring (Clupea pallasii). When herring spawn finished by March, birds move farther offshore, although still over continental shelf, then back to colony areas (150, 126). During earlier years, Oregon and Washington birds may have moved south (84). In California, and elsewhere, occupies productive areas not reachable during breeding, e.g., Monterey Bay for Farallon Islands breeders. Associated with 40-m contour, especially in more sheltered Half Moon and Monterey Bays (84, 122, 112, 151, DGA).
In eastern Canada, occurs over continental shelf from southern limit of sea ice south to within a few hundred kilometers of southernmost breeding sites. Winters as far south as February 15°C sea-surface isotherm (38, 152, 87, 88, 8, 90). In United Kingdom, murres breeding at Isle of May winter in shelf waters of North Sea to the north and somewhat in waters to the south (92); those breeding at Skomer Island winter in waters off south coast of Ireland and England, south to Brittany and Bay of Biscay (91). In waters off Europe, particularly well-studied in North Sea, movements somewhat affected by sea surface temperature, e.g., molting where/when temperatures are warmest (92).