SPECIES

Common Murre Uria aalge Scientific name definitions

David G. Ainley, David N. Nettleship, and Anne E. Storey
Version: 2.0 — Published August 6, 2021

Diet and Foraging

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Feeding

Main Foods Taken

Micronektonic prey, 2–25 cm in length (mainly 6–10 cm), including fish, euphausiids, large copepods, and squid. In summer mainly fish, especially when feeding chicks, in contrast to a more diverse diet during non-breeding period, with euphausiids in particular more important (169, 170, 171, 142, 172, 112, 173, 174, 109, 175; see below, Diet; Appendix 10, Appendix 11, Appendix 12).

Microhabitat for Foraging

Feeds on or, more usually, above bottom, over flat or varied relief and composition (e.g., 171, 142, 112), especially where ocean processes concentrate prey (115); see Habitat: Habitat in Breeding Range. In California Current, concentrated numbers of murres foraging in nearshore, shelf waters, appear to force competitors, such as shearwaters (Ardenna spp.), to forage in deeper waters, though the murres can dive much deeper (115). Critical is the frequency in which high quality prey patches adequate for efficient foraging are encountered and, as judged for capelin (Mallotus villosus), the density of such patches within the foraging area of a colony increases with regional capelin abundance (146).

Foraging Range (While Breeding)

In California Current, mostly concentrates within 40 km of colonies (84); maximum foraging range during chick-rearing at least 70–80 km, but in many years within 1 km depending on prey type and availability (111, 102, 83). Similarly, depending on prey availability, birds forage near to the colony in Barents Sea (176), and at Isle of May, northeastern Atlantic (92). The pattern is also evident elsewhere; for instance, at Pribilof Islands, Alaska, foraging range varies from 8–60 km (131); a range similar to that has also been reported for Tatoosh Island, Puget Sound, Washington (177). In Newfoundland, at Witless Bay, foraging range during incubation to 120 km (median 37.8 km), but during chick-rearing to 80 km (median 5.4 km in mid-1980s [178]; within 5 km in late 1990s [179]). At Funk Island, foraging ranged 60–81 km away depending on availability of energy-rich capelin (180; see also 176). Chick-rearing murres returned to the places where they have successfully foraged previously, suggesting that memory is important (181), and thus once in the general area (<2km), they are able to concentrate their search to find prey (182) including using local enhancement (observations of foraging by other seabirds) to refine their search (181).

Food Capture and Consumption

Diving

Prey captured in bill by diving, using wings for propulsion. Wing musculature and bones less specialized than in penguins, consistent with both aerial and underwater flight (183). Long, slender tongue, enclosed along entire length of bill by sharp edges, helps to “lock” prey against backward-pointing palate denticles (184). Dives deep for a relatively small bird (cf. loons, penguins), often to 70 m and occasionally to 180 m (185, 186, 142, 187, 188, 189), although normal feeding depth 20–50 m (185, 190, 191). Depth of dive 100% greater than that predicted in relationship of diving depth to body mass for auks and penguins (192), perhaps not surprising once depth of neutral buoyancy is considered, which in murres is approximately 70 m (193, 188). Chick-rearing murres make deep dives (50–150m) during daylight to reach fish that are easier to catch because they are in the cold intermediate layer of the water column in both Newfoundland (194) and the Bering Sea (195). Breeding success was reduced in a year when fish were deeper than this layer and less abundant (195). Diving speed on order of 1.5–2 m/s, with maximum 2.6 ± 0.2 m/s (185, 196, 197). Forages during day-light or crepuscular periods (111, 198, 199, 92); captive murre unable to capture prey in the dark (200). Under natural conditions murres do dive at night (194, 92), but they use shallower dives to take advantage of the diel vertical migration of fish, which are near the surface at night (201). Murres are able to adapt their diving behavior to light conditions and the diel vertical migration and catchability of their prey (194). Nocturnal dive depth is greater when the moon is full compared to partial moonlight, and while some diving still occurs under darker conditions, foraging efficiency is lower and is likely confined to successful locations identified by daylight (201). Crepuscular foraging is also common, when capelin are moving upward and downward in the water column as part of their diel vertical migration (189). Similar circadian variation in dive depth has also been observed for murres foraging on a variety of prey species near the Aleutian archipelago (202, 203). In both auks and penguins, wing area (cm2) increases directly with (log) body mass and with common slope, but for a given body mass, murre wings much smaller and thus less optimal for subaqueous flight; however, wing area:body mass relationship for Great Auk (Pinguinus impennis) and molting Common Murre closest of all alcids to penguin relationship (192; see also 204).

On foraging trips, as observed at Witless Bay (Newfoundland), adults spent 5–14% of time diving for prey, 79–83% on surface, and 10% flying to and from colony (178). In waters around the Isle of May on a given day, murres spent much more time diving than flying; they spent more time flying during the breeding season (92). Time submerged varies with depth, increasing from an average 15 s in waters <2 m deep to 61 s in waters >8 m deep (205). Dive duration ranges 0.9–1.2 min, and up to 3.4 min, and on average dive duration is longer than in penguins once body mass is accounted for (206). Average dive time off Washington 41 s (207), off central California at Farallon Islands 55 s (111) and in coastal Monterey Bay 37 s (199), and off Oregon 71 s (208); maximum dive time at these locations 70, 71, 193, and 140 s, respectively. Dive-pause (amount of rest between dives) ratio 3.6 in shallow to 4.8 in deep water off Scotland (about 8 m; 205); 3.1 in Yaquina Bay, Oregon (10 m deep; 208); 5.2 off Farallon Islands, California (>8 m deep; 111), and approximately 2.0 in Monterey Bay (199). During food shortage, trips much longer in distance (see above) and duration, and more time spent diving; foraging time taken from time spent at colony, hence less colony attendance during food shortage (209; see Breeding: Colony Attendance). Compared to Fratercula (and presumably other smaller alcids), forages in shorter sequences, with fewer dives (0.5–0.6 dives/min; 210).

Foraging Behavior

Likely more agile than Thick-billed Murre (Uria lomvia) underwater, but probably slower, when diving to shallower depths (211, 188). There appears to be segregation in foraging where Common Murre overlaps with Thick-billed Murre, with Common Murre foraging deeper with more active wing strokes at bottom of dive, capturing more active fish than Thick-billed Murre; they have a similar diel pattern of diving (212). Greatest overlap with Thick-billed Murre chick and adult diet when food is abundant (176), and greatest segregation under conditions of food stress (warmer water temperature) as measured with stable isotope analysis (213). Foraging Common Murre maintain similar distances from conspecifics and other seabirds, whereas Marbled Murrelets (Brachyramphus marmoratus) maintain a larger distance from murres than to each other, indicating that there are competitive interspecific interactions that do not favor murrelets (214).

Forages alone or in single-species and multispecies flocks (see Behavior: Social and Interspecific Behavior). Day to day, or within days, may use widely separated feeding areas, indicating awareness of several options (215, 216, 102, 83). Little support found recently for “information-center” hypothesis (217; see also 218); departing murres do not cue in on arrival directions of successful foragers. Rather, birds return to where previously successful (179). Murres forage at prey patches (fish schools) within larger regions of enhanced prey availability (134, 219, 181). Benoit-Bird et al. (202, 203) used sonar to detect prey patches and counted the number of bubble trails from diving murres to show that murre density was related to fish density, but not related to specific prey species.

Most successful prey capture in pursuit of single prey, ignoring others present (200, 220, 212). Solitary fish were targeted in 69% of active foraging attempts even though capelin were aggregated in large schools in almost all underwater observations near foraging murres (91% of observations, 220). Descends quickly, almost vertically (188), apparently entering schools from below after pace is slowed. In case of slow-moving prey (e.g., euphausiids), dives without seeming to coordinate with other birds; surfaces well ahead of those about to dive, then swims back to main aggregation; progression at same pace as moving school, with flocks progressing in different directions (221). When feeding over fast-moving schooling fish (e.g., anchovy), murres are spaced about 1 m apart in long lines; dive and surface in concert, which suggests cooperative foraging (DGA).

Consumes prey mainly underwater, at times on surface; fish seized somewhere behind pectoral fins, then, by short bites, aligned for swallowing head first (200, 11). Therefore, long, thin, fusiform prey preferred (prey body depth <4.0 cm, 222; see above, Main Food Taken). Digestion rapid: 20-g spratt (Sprattus sprattus) fed to captive murres (stomachs empty) passed through stomach within 15 min, and entirely through gizzard within 45 min (using X-rays; 223).

Olfaction

Not associated with foraging in this species.

Diet

Major Food Items

More (but not exclusively) piscivorous than Thick-billed Murre (Uria lomvia), as judged on morphology and confirmed by diet (184, 211; see below). Diet remarkably well studied for western North American populations throughout annual cycle, but incompletely known for eastern North America and Europe (studied mainly during chick-rearing; see Appendix 10, Appendix 11, Appendix 12). Winter diet in eastern North America was historically capelin (38), but is currently partly at a lower trophic level indicating some invertebrate consumption (224, 168). In accord with greater latitudinal spread of populations, and more research, about 36 prey species identified along eastern Pacific Ocean/Bering Sea coast versus about 20 species in North Atlantic. Fish predominate during summer, small cephalopods and euphausiids during winter and early spring. In case of fish species that attain large size as adults, juveniles are important prey, e.g., Atlantic cod (Gadus morhua), rockfish (Sebastes spp.), pollock (Gadus chalcogrammus); owing to growth in size, these prey become unavailable by late fall (225, 112).

Adult, Summer

Mostly fish, both benthic and midwater (Appendix 10, Appendix 11, Appendix 12). Levels of stable isotope of Nitrogen (N) in muscle (expressed as δ15N) 15.5 ± 1.5 SE (n = 6) from Queen Charlotte Islands, British Columbia, and 15.3 ± 0.9 (n = 5) from Shumagin Island, Alaska, ranking it as the most piscivorous (fish-eating) marine avian species of eastern Gulf of Alaska (130); values of 14.8 ± 0.9 (n = 3) from Farallon Islands, California, indicate slightly less piscivory in California Current, especially compared to more piscivorous species (226). As capelin (Mallotus villosus) became more abundant, and murre diet concentrated more on them, δ15N increased from 13.97 ± 0.36 to 14.78 ± 0.40 in waters off Newfoundland, with similar values among Razorbills (Alca torda), but slightly higher than in Atlantic Puffins (Fratercula arctica; 227).

Tends to need high density of abundant, schooling forage fish during breeding season, owing to high energy life style and need for single-fish delivery to chicks. In Gulf of Alaska (Appendix 10): capelin, herring (Clupea pallasii), juvenile walleye pollock/Alaska pollock, and sandlance (Ammodytes spp.; 228, 229, 230, 37, 231); Bering Sea shelf: juvenile walleye pollock (138, 134, 144); northern Bering Sea: arctic (Boreogadus saida) and saffron (Eleginus gracilis) cod (139); in California Current (Appendix 11): juvenile rockfish (Sebastes spp.), anchovy (Engraulis mordax), salmon (Oncorhyncus spp.), smelt (Osmeridae), and sandlance (Ammodytes spp.; 83, 102, 85, 232). In northwest Atlantic: capelin (171, 181, 233, 234) and alternate prey when capelin are less available, including sandlance (up to 45% sandlance in worst capelin year, 234), and daubed shannies (Lumpenus maculatus; 235); in northeast Atlantic/North Sea region (Appendix 12): capelin, herring (Clupea harengus), and sandlance (174, 236, 175); northern Norway: juvenile Atlantic cod (Gadus morhua), saithe (Pollachius virens), and haddock (Melanogrammus aeglefinus), as well as the more typical forage species (109); Barents Sea: capelin (107, 237, 219, 146); Baltic Sea: sprat (Sprattus sprattus; (238, 239).

Prey varies with respect to foraging habitat, e.g., sandlance, anchovy, and smelt taken in sandy, inshore areas; rockfish, capelin, and pollock taken farther offshore (240, 102). Murres show individual differences in the degree of diet specialization, even in a year of abundant capelin availability (as exemplified at Cabot Island, Newfoundland; 241).

Chicks

Chick diet as returned by parents to the breeding ledges can differ markedly from adult diet. In northern Norway, chicks were fed mainly capelin and sandeels, while adult diet consisted mainly of juvenile cod and haddock (242). On the other hand, in central California, chick diet prior to fledging very similar to that of adults (112). Adults preferentially feed energy-rich prey to chicks: in western Atlantic, capelin (e.g., 90% of diet at Great and Gull Islands., Newfoundland, 1982–1984 (142); 79% of diet at Gannet Islands, Labrador, 1981–1983 (243, 244, 171, 245, 246, 234); in Barents Sea region, capelin, sandlance, and herring dominate with capelin often 60–100% of the diet (237); in North Sea, sandlance was initially 40–65% of diet (236), shifting to clupeids in early 2000s (174, 175); at Skomer, herring and spratt (Sprattus sprattus; 247); in central California, Farallon Islands, diet 90% rockfish if available close to colony, otherwise 90% anchovy (more energy dense but farther away) if rockfish not available (102, 82, 83), though in coastal northern California, feeding chicks on anchovy, rather than closer rockfish and smelt, leads to reproductive failure (232). Chick diet also reflects prey availability, which can be affected by both local and remote parameters, including upwelling, tide, and decadal oscillations (248, 102, 232), as well as fisheries management (238, 249). Accordingly, pollock have increased and capelin decreased in Bering Sea and northern Gulf of Alaska diet (250, 251, 103); anchovy and sardine have replaced rockfish in California Current, subsequently reverting (112, 103, 102, 83); spratt have at times, especially recently, replaced sandlance in the diet of murres in North Sea (236, 175); and in North Atlantic waters off Wales, since the early 1970s, the prevalence of herring (Clupea hargenus) and spratt has decreased from being 70–90% of diet, and being replaced somewhat by gadids of several species (gadids now 50-65%; 247). In the Baltic Sea, the increased availability of high quality spratt (fatter life stages), owing to fish depletion cascades, led to increased breeding success and murre population increase (238, 252). Likewise, fishery related changes in prey availability led to altered chick production and corresponding decrease or increase in murre populations in central California (102, 82). Spawning capelin are also the main forage fish fed to murre chicks in the western North Atlantic, with capelin abundance being related to pre-spawning ice conditions that affect capelin foraging success and development (253), as well as cold February to June sea temperatures that delay gonadal development (254). In years with low capelin abundance, chicks are fed alternate prey such as daubed shannies (235) and sandlance. In a 23-year study on Funk Island, Newfoundland, murres returned to the colony with gravid female capelin (44% of samples), which was more than other seabirds that had less need to target the highest energy available prey (255). Montevecchi et al. (234) documented the decline of capelin populations near Funk Island (the largest western Atlantic Common Murre colony), and noted that chick mass at fledging has decreased but adult condition has remained stable even though parents were working harder (i.e., flying farther to get food). Chick growth can also be affected by prey quality as well as quantity (256, 238).

Adults, Winter

Especially midwater crustaceans (e.g., euphausiids), which are more prevalent in diet than during summer; amphipods, euphausiids, and other crustaceans ≥70% of eastern Newfoundland diet, 1984–1998, >90% of Kodiak Island, Alaska diet, and >90% of Farallon Islands, California diet (257, 112, 258); among non-breeding birds in Monterey Bay, California, market squid (Doryteuthis opalescens) can contribute almost 50% of diet (199; Appendix 10, Appendix 11, Appendix 12). Midwater crustaceans also dominate diets year-round in pelagic waters (259). Burke and Montevecchi (168) noted that capelin, arctic cod, and zooplankton were likely eaten by adult Common Murre (no good data for diet in winter), based on data from Thick-billed Murre and young Common Murre that normally feed at a lower trophic level than adult Common Murre.

Food Selection and Storage

Selects prey suitably shaped, preferably long and thin (222, 196), as well as prey of high energetic value (245, 260; see above, Diet). Does not store food. Chicks refuse to accept deep-bodied prey, which are difficult for them to swallow, such as Pacific butterfish (Peprilus simillimus; 111; see 222, 196). Chick and male parent at sea share same diet (261, 112).

Nutrition and Energetics

Daily energy expenditure is several times higher during breeding, up to >1000 kJ/d, than during the non-breeding period, owing to increased requirement for flight; especially low during molt (92). Water temperature importantly affects energy expenditure (92). Eats 10–30% of body mass daily, or 90–300 fish/d (262, 222). A captive murre required 28% of body mass in energetically valuable fish/d (trout; Salmo) in order to maintain body mass (200); without feeding lost 2.8–5.7% of mass/d. Deprived of food, begins to feed immediately when food available. In accord, 300 g/d and 100 g/d required by an adult or chick, respectively, during summer (263; see Conservation and Management: Effects of Human Activity). During first 16 d (linear phase of mass change), chicks require 27–49 g fish/d (244, 264), depending on caloric value (245). Conversion efficiency of fish consumed to chick growth ranges 18–31%/d, but sensitive to number of meals, size of fish, and chick mass change (264).

Metabolism and Temperature Regulation

The difference or ratio of field-metabolic rate (FMR) to resting-metabolic rate (RMR) indicates the energetic cost of activity. Mean FMR of 17.9 W/kg ± 2.6 SE is 50% higher than predicted on basis of allometry; likewise basal metabolic rate (BMR, or RMR) of 3.6 W/kg ± 0.7 SE is also higher than expected (260). Other directly measured BMR (RMR) results also high relative to expectation: e.g., 6.8 (262), 6.0 W/kg (6.1 in water; 265), for energetically costly reasons explained below. Foraging demands increase during winter, and for males with fledged chicks (266, 168); males with chicks at sea spent twice as much time foraging as females (266). As such, energy requirements nearly double for murres at the end of winter in the northwest Atlantic, and murres exceed 7 times basal metabolic rate during this time, exceeding the maximum thought to be sustainable for vertebrates (168). Similar pattern observed in northeast Atlantic (92).

Slope of regression line of metabolism to ambient temperature and heat loss coefficients are also high compared to arctic species of similar size. Therefore, high metabolic activity, and not insulation, maintain homeothermy at cold temperatures, as in smaller species (262).

High metabolic rates, and high daily energy expenditure, also result from energetically costly flight and foraging (diving; 260, 92). Significant positive correlation between FMR and time at sea, with ratio of FMR/RMR varying 1.7–6.8 (267). Accordingly, myoglobin concentrations in flight muscles much higher than in terrestrial birds or even penguins; anaerobic glycolysis during diving not used extensively, as true in penguins (268, 269, 270). High cholesterol levels in blood, relative to nondiving birds, related to high fat content of prey required to sustain metabolism and activity (271).

Due to energetically costly activities and large populations, consumes great quantities of fish and dominates energy expenditures of multispecies colonies, as in coastal Oregon (272, 273), Pribilof Islands, Alaska (132), Prince William Sound, Alaska (231), Barents and Norwegian seas (274), and Gulf of the Farallones, California (83). Both Common and Thick-billed together can dominate energy expenditures of entire seabird communities (e.g., Bering Sea during summer), expending 79 MW/Mm2 (M = mega), second only to Ardenna spp. (275). Entire murre population of eastern Bering Sea and eastern North Pacific (both Common Murre and Thick-billed Murre) may consume about 945 tons fish/d, constituting highest take by all resident seabird species (172); similar scenario in Prince William Sound, Alaska, where in winter the seabird community consumes 2,409 tons, up to 80% by Common Murres (231). A simulation model estimated energy needs in California Current off Oregon: winter (November-March) 306 kcal/d, prelaying 294–306 kcal/d, laying 296 kcal/d, chick-rearing 280–290 kcal/d, molt 299 kcal/d, and fall (warm weather, August–October) 276–294 kcal/d (272). High levels of prey consumption brings conflicts with commercial fisheries (see above; also Conservation and Management: Effects of Human Activity).

Corticosterone (CORT, the main glucocorticoid in birds) levels are elevated in Common Murre under difficult foraging conditions (276, 277), and in both Common Murre and Thick-billed Murre when they carry geologgers (278), which affect foraging efficiency. A multi-year study showed that Common Murres have higher CORT levels in years with intermediate foraging conditions than under good or poor conditions, suggesting that murres elevate CORT when greater foraging effort is likely to increase food intake, but not when conditions are so poor that extra foraging effort is unlikely to make a difference (279).

Murres lose body mass after their chicks hatch (280, 281, 282), and they lose more mass in years of poor food availability (281). Fluctuations in body mass are due to changes in lipid losses or gains (282). Beta-hydroxybutyrate levels, a measure of lipid metabolism, were higher in murres sampled in mid chick-rearing during a good foraging year compared to intermediate and poor years, suggesting that mass loss was delayed in good years and was still ongoing when murres were captured in good years, but already completed in poorer years (279). Haematocrit levels were higher in intermediate years than in good ones, suggesting that murres were working harder under less optimal conditions (279), as high haematocrit levels are associated with longer dives in seabirds (283, 284). Thick-billed Murre with particularly difficult winter foraging conditions had shorter telomeres than birds with greater foraging opportunities (285). Taken together, this information suggests that though murres appear to compensate to a wide range of foraging conditions, there are considerable physiological costs resulting from difficult foraging conditions.

Drinking, Pellet-Casting, and Defecation

Presumably drinks seawater, excreting excess salt through large supraorbital glands (DGA and DNN). On breeding cliffs, defecates in all directions; birds that have incubated eggs or brooded chicks for a time become splashed with guano from neighbors. Does not make pellets.

Recommended Citation

Ainley, D. G., D. N. Nettleship, and A. E. Storey (2021). Common Murre (Uria aalge), version 2.0. In Birds of the World (S. M. Billerman, P. G. Rodewald, and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.commur.02