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

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Identification

Medium-large dark brown-and-white seabird (body length 38–43 cm, wingspan 64–71 cm; 800–1,125 g; Appendix 1). In Definitive Alternate (breeding) plumage, upperparts including head, neck, back, and upperwings brown to blackish brown; underparts mostly white; flanks and thighs striated brown and white. Secondaries tipped white, imparting a white trailing edge to closed wing. Dark color fades noticeably by late summer, especially on primaries. Bill entirely black and stiletto shaped. In the Atlantic region, most populations of Common Murre include “bridled” individuals, distinguished by a white eye-ring and a white line extending backward along an ocular groove, which is most obvious in breeding plumage (see Systematics: Geographic Variation). Only once has a bridled Common Murre been recorded in the Pacific region, at the Farallon Islands, California, either as a vagrant or genetic anomaly (1).

Juvenile, Formative, First-Alternate, and Definitive Basic plumages are similar to breeding except for head: “chin, throat, and cheeks white, the latter extending upward behind eye and crossed by diagnostic black postocular stripe. Hindneck dark, extending as partial collar at base of white foreneck” (2: 395). Plumage variable, with some birds (often those in Second Basic Plumage) with dark mottling or occasionally entirely dark heads, resembling Definitive Alternate Plumage (3).

Similar Species

Common Murre is distinguished from very similar Thick-billed Murre (Uria lomvia) by a longer, thinner bill, tapering gradually to the tip, compared to notably decurved culmen in Thick-billed Murre (ratio of bill length:depth 3.2 in Common versus 2.4 in Thick-billed; cf. 4, 5; see also Measurements); longer, slimmer body and neck; bill dark along tomium (Thick-billed has white stripe along cutting edge of upper mandible, except for some individuals during winter); dorsal body plumage overall browner; streaking on flanks and underwing coverts darker; and white of breast meeting brown throat in a straight line or a shallow, inverted “U” (compared to a sharp “V” in Thick-billed Murre). Distinguished from Razorbill (Alca torda) by much slimmer build, browner coloration, and much longer, sharper bill (Razorbill's bill deeper and blunter, more laterally flattened or “puffinlike”). Common Murre chicks fledge early and can be confused with murrelets, but when this small they are attended to by male parent (see Breeding) and their feathering is loosely textured ('fluffy') unlike murrelets found at sea .

Plumages

Common Murre has 10 full-length primaries (numbered p1–p10 distally), 15–16 secondaries (numbered s1–s12 or s1–s13 proximally, and including 3 tertials, numbered t1–t3 distally), and 14 rectrices (numbered r1–r7 distally on each side of the tail); most alcids, including murres, are diastataxic (see 6), indicating that a secondary has been lost evolutionarily between what we now term s4 and s5. Geographic variation in appearance slight (see Systematics: Geographic Variation) and some geographic variation in the timing of molt evident (see Molts).

Natal Down

Hatchlings completely downy. Down medium gray, with no trace of brown brindling as in Thick-billed Murre (Uria lomvia; 7); paler below, with silvery tips to down on head and neck (8). Feet dark gray; toenails black.

Juvenile Plumage

Present primarily July–September. Before fledging, Natal Down replaced by filamentous juvenile body feathers and weak juvenile primary coverts while juvenile remiges are developed at sea, following fledging (9). Juvenile Plumage resembles Definitive Basic Plumage, except that prominent white postocular streak may or may not exist and a diffuse gray collar varies in prominence (8: 134). In Barkley Sound, British Columbia, 1979–1980, all Common Murre chicks with male parents had white-tipped secondaries and many but not all large chicks had a faint lower neck-ring caused by lightly flecked feather tips; ring only rarely and partly retained by midwinter (H. R. Carter and S. G. Sealy, unpublished data).

Formative Plumage

Present primarily September–April. Formative Plumage similar to Definitive Basic plumage, except for browner and more worn upperwing primary coverts contrasting with fresher upperwing greater coverts, back, and primaries (10, 9; and see Molts). Birds in first year also separable from adults by smaller bills, skull ossification, and width of the premaxillary process (see Bare Parts). Head plumage variably dark, but usually not completely dark as some birds show in Second and Definitive Basic plumages (3).

First Alternate Plumage

Present primarily April–July. Most individuals fail to acquire completely dark heads as in Definitive Alternate Plumage, thus most resemble Definitive Basic plumage, but some do resemble Definitive Alternate plumage or appear intermediate, with mottled black and white feathering in head (11, 12, 13, 14). Browner and more worn upperwing coverts, and bill and skull criteria (see Formative Plumage) continue to be useful in distinguishing individuals in First Alternate Plumage.

Second Basic Plumage

Present primarily September–January. Second Basic Plumage is essentially indistinguishable from Definitive Basic Plumage although the percentage of birds with dark heads appears to average greater in Second than in later Definitive Basic Plumages (3). Bill size and premaxillary ("gape") width can still be used to identify some second-cycle birds (see Bare Parts).

Definitive Basic Plumage

Present primarily September–December (southern populations) or September–March (northern populations). Duration of time in Definitive Basic Plumage may decrease with age, from entire winter for some individuals (Second Basic Plumage?) to hardly at all for some older adults (e.g., 18 d reported for breeding adults >3 yr; 15). Throat, sides to neck, and face mostly white except for dark streak extending from behind eye toward nape. Otherwise, upperparts uniform dark brown, in worn plumage showing pale tips to back and upperwing coverts; a small area of white shows on trailing edge of wing, formed by white tips to inner secondaries; remainder of underparts white; flanks streaked to varying extent with blackish brown. Underwing coverts white, sometimes lightly mottled brown, glossy blackish below remiges (from 8: 134; also 2). Distinguished from Formative Plumage by all upperwing coverts being uniform in quality, without brownish cast (10, 9).

Definitive Alternate Plumage

Present primarily November–August (southern populations) or March–August (northern populations). Similar to Definitive Basic plumage, except head, throat, and upper breast dark brown and similar to darker upperparts, but head more chocolate brown. “Bridled” morph (up to 50% of population in some parts of Atlantic) has white eye ring from which a narrow white line extends back behind eye, highlighting a narrow groove in feather coat (present in all morphs; see Identification; also 2, 8 for more details). Duration of time in Definitive Alternate plumage increases with age, about 5 weeks in 2-yr-olds, to 8.5 months among breeding adults (>4 yr; 11, 15).

Aberrant Plumage

Melanistic and albinistic individuals rare (2). At least two completely dark Common Murres recorded at or around Southeast Farallon Island, California (3); may result from melanism or possibly from a molt-plumage interaction (see Molts). Male at Cape Thompson, Alaska, had white postocular groove, but no eye-ring (i.e., incomplete bridling; 16), whereas a completely bridled individual on Farallon Island, California, may have been either a vagrant from the Atlantic or an anomalous individual (1). Bridling can vary; most birds as described, but rarely, markings may be thinner, or no spectacle, or no white groove behind eye (17). Individuals at sea for long periods may acquire growths of diatoms on breast feathers, which discolor the plumage, appearing at times like patches of oil (18).

Molts

Molt and plumage terminology follows Humphrey and Parkes (19) as modified by Howell et al. (20, 21). Common Murre exhibits a Complex Alternate Strategy (cf. 20, 22), including complete prebasic molts, a partial preformative molt, and limited-to-partial prealternate molts in both first and definitive cycles (10, 9; Figure 1). See Pyle (9) for various interpretations of first-cycle molts.

Prejuvenile Molt

Complete, primarily July–September. Body-feather molt completed by August, usually before fledging, but growth of remiges protracted through October, overlapping Preformative Molt of body feathers and rectrices (9). By 14 d, hatchlings acquire a dark-gray mask, white throat, white cheeks, and a white line running back and down from eye; some variation in amount of white on cheeks and behind eye. In Thick-billed Murre (Uria lomvia), and probably Common Murre: “Pin-feathers visible on wing at 5 d; begin to burst from sheaths at 1–10 d; by 14 d most contour feathers are developing, and by 18 d all down replaced except on head. At ledge departure, chick fully feathered except remiges and rectrices”; only upperwing primary coverts fully grown (5: 22; 9).

Preformative Molt

Partial, primarily August–October. Includes all body feathers and rectrices, mostly all upperwing secondary coverts (a few outer greater coverts occasionally retained), but no primaries, primary coverts, or secondaries. Preformative Molt overlaps with initial growth of remiges during Prejuvenile Molt (10, 9). See Pyle (9) for details including assignment of molt terminology.

First Prealternate Molt

Perhaps absent but otherwise limited, primarily February–May. Appears to involve head and breast feathers only, as in Definitive Prealternate Molt, though a few to many formative feathers may be retained in these areas. There is little evidence of color-pattern change (see First Alternate Plumage), indicating either a lack of molt or that first alternate feathers can be patterned like formative feathers; study needed.

Definitive Prebasic Molt

Complete, primarily July–October, but may commence as early as May–June in southern populations (U. a. californica, U. a. albionis), in which molt is best studied. Timing and duration vary annually in southern populations (presumably in relation to food availability; 15); therefore, likely to vary by latitude as well. Oregon birds (that winter in more productive central California Current) tend to breed and molt slightly earlier than those from Washington and British Columbia (23, 24; H. R. Carter and S. G. Sealy unpublished data). In Atlantic, northern populations also molt later (and breed later) than southern ones (12). Timing varies also by age and sex; subadults (e.g., undergoing the Second Prebasic Molt) and failed breeders molt first, followed by successful females (who continue to visit colonies after chick departure), and finally successful males (attending chicks at sea); however, much overlap exists between birds of different status (15, H. R. Carter and S. G. Sealy, unpublished data). Off Washington, no evidence for annual difference in molt timing between sexes within age classes (23). In southern populations, molting birds appear as early as July (or as early as mid-May for the Second Prebasic Molt; 3), with first fully molted and flying by September; all birds have replaced flight feathers enough to fly by November (U. a. californica and U. a. albionis; 15, H. R. Carter and S. G. Sealy, unpublished data, DGA). See Pyle (3) for interactions between molt timing and plumage coloration; earlier prebasic molt (e.g., the Second Prebasic Molt) appears to result in darker basic feathers.

Duration of entire molt in U. a. albionis <70 d in breeding adults and birds >3 yr of age; longer in younger birds, up to >120 d (25, 15). In U. a. californica off Washington, primary molt required about 25 d in 1996, but 75–81 d in 1993 (El Niño); secondary and rectrix molt required 72% and 65% as much time, respectively (23). In a captive population, duration was 51.7 d ± 5.3 SE (25); faster in wild populations by 18–23 d (26, 15).

Definitive Prebasic Molt involves all or almost all contour and flight feathers (12, 14, 23, 10, 9). Primary and secondary molt rapid, reported to begin between p4 and p7, progressing proximally and distally (23). Secondary molt begins when primaries are about 38% grown and ends when primaries are about 99% grown. Secondaries lost and may be regrown beginning at 3 foci, proceeding proximally from s1, proximally from s5, and both proximally and distally from the middle tertial, t2, as in other diastataxic species (10). Rectrices lost and regrown in no discernible order; begin to regrow when primaries and secondaries 43% and 20% grown, respectively, but growth completed when latter only 81–88% grown. Loss of flight feathers so rapid that previous, more cursory observation led to conclusion that flight-feather molt was synchronous or simultaneous (reviewed by 23: 660); rapid replacement may lead to variation in flight-feather replacement sequences indicated above. Sequence speculated to be similar to other disparate avian groups (e.g., parrots [Psittacidae]); likely a trait that evolved in an ancestral auk (23).

Owing to rapid, near-simultaneous flight-feather molt, murres rendered flightless. Loss of “flight” efficiency (aerial and subaqueous) confined to late summer and early fall, when food availability is high and predictable in molting areas and there is no need to occupy breeding sites. Males attending chicks at sea do not fly or leave chicks in any case and, thus, are behaviorally flightless prior to Definitive Prebasic Molt.

Definitive Prealternate Molt

Limited, primarily November–April, with timing varying substantially with latitude of breeding. In southern populations (U. a. californica and U. a. albionis), majority complete molt by January–February (15, H. R. Carter and S. G. Sealy, unpublished data, DGA), with some completing it by late November (3). In northern populations, complete Definitive Alternate Plumage not seen until March (U. a. aalge of Newfoundland and, presumably, U. a. inornata of Bering Sea; 8). Onset can vary annually but, in southern populations, occurs well before breeding when sites occupied early as October (see Breeding: Colony Attendance). In some years, females may begin molt sooner than males; onset not related to date when adult left colony in previous breeding season, laying date the next season, or body mass (27, 15). Includes head and breast feathers.

Bare Parts

Bill and Gape

Bill black, gape creamy yellow.

Iris and Facial Skin

Iris is dark brown or black.

Tarsi and Toes

Light brownish gray, toes and webs sometimes yellowish; nails black.

Measurements

Linear Measurements

Little sexual dimorphism, but males slightly larger in culmen length, bill depth, and tarsus; females perhaps slightly larger in wing length (Appendix 1). Wing length and bill depth significantly less in 1-yr-olds. Longest primaries frequently abraded, losing several millimeters in length by end of chick-rearing period. In fresh plumage, adult males (n = 20) have significantly longer primaries, shorter secondaries, and longer rectrices than females (n = 15) (in mm): males 1113.0 ± 3.5 SE, 1012 ± 7.1 SE, 301.4 ± 4.4 SE, versus females 1095.7 ± 10 SE, 1031.6 ± 8.7 SE, 289.6 ± 3.0 SE (23).

Culmen longer, thinner, wings smaller in U. a. californica than U. a. inornata (Appendix 1). Both Pacific subspecies larger than U. a. aalge (all populations). Northern populations of U. a. aalge larger than southern, especially wing length. Longer wings, therefore, in populations that move farthest from breeding sites during winter, which is true of migratory species (e.g., 28). Male's longer wings needed to support heavier body mass; see discussion of wing-loading in Behavior: Locomotion.

Mass

Among breeders, varies between and within years. Adults at sea, including those tending chicks (and/or in molt in case of females) heaviest; adults feeding chicks at the colony lightest (16, 29; DGA and L. Spear, unpublished data; see below). Both sexes lose mass from prelaying to chick-rearing, and females continue loss during period when they visit breeding ledges after chick fledging (30). Molting (flightless) birds heavy, but lighter during food shortage; e.g., El Niño (23; DGA and L. Spear, unpublished data; and see 31). Mass varies also between sexes (males heavier) and age classes (adults heavier, except during molt; 32, 31; DGA and L. Spear, unpublished data). In arctic Alaska, mass of breeders varies inversely with sea-ice cover, with greater cover decreasing feeding efficiency (16).

Selected body mass data (g) as follows for U. a. californica, central California coast, 1985–1988 (DGA and L. Spear, unpublished data): prelaying adult male 991 ± 69 SD (n = 40), adult female 991 ± 66 SD (n = 30), subadult male 951 ± 78 SD (n = 15), subadult female 929 ± 58 SD (n = 22); incubation adult male 1,027 ± 80 SD (n = 16), adult female 994 ± 58 (n = 22), subadult male 900 ± 29 SD (n = 5), subadult female 900 ± 45 SD (n = 6); chick-rearing-colony adult male 958 ± 87 SD (n = 6), adult female 928 ± 11 (n = 3); chick-rearing-at sea/molt adult male 1,043 ± 82 SD (n = 8), adult female 990 ± 52 SD (n = 3), subadult male 1,055 (n = 2); winter adult male 958 ± 31 SD (n = 4), adult female 1,000 ± 35 SD (n = 5). Data from other areas not significantly different; see Johnson (33), Swartz (16), Threlfall and Mahoney (32), Piatt et al. (34), and Thompson et al. (23).

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