Common Gull Larus canus Scientific name definitions

William Moskoff, Louis R. Bevier, and Pamela C. Rasmussen
Version: 1.1 — Published August 18, 2021
Revision Notes

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Introduction

The Common Gull is a rather small white-headed gull with no distinct bill spot that is very familiar across much of Eurasia. When lumped with the Short-billed Gull L. brachyrhynchus, as has long been the case until very recently, the combined species has also been called Mew Gull in some global sources, but this has never gained wide usage in the Old World. The northeast Asian form known as "Kamchatka Gull" has also sometimes been considered a separate species but is evidently more closely related to the nominate than to L. brachyrhynchus.

Many aspects of the biology of the Common Gull have been studied, including the relationship between sexual and agonistic behavior (1), breeding behavior in Ireland (2), growth energetics (3), habitat selection in Poland (4), nest-site selection in Finland (5), population ecology in Estonia (6), and nest-defense behavior in Finland (7).

Identification

Medium-small gull. Total length 41-46 cm; nominate 290–552 g, kamtschatschensis 394–586 g; wingspan nominate 110–125 cm. Male averaging slightly larger and heavier than female. A rather delicately built gull with gentle appearance due to rounded head, relatively large eye, and slender, short bill that has a gradual curve along distal portion of culmen and shallow gonydeal angle; wings relatively long and slender. Floats buoyantly with much of body above water, wings and tail projecting upward at slight angle; often feeds on water by spinning and picking delicately from surface. When foraging over water, often flutters wings and stoops with dangling legs and head down to pick at surface.

Adult breeding (Definitive Alternate) plumage characterized by entirely white head, tail, and body, medium-gray mantle (back, scapulars, and wing coverts), large white tertial-crescent (tips of tertials), small white scapular-crescent (tips of lower scapulars), and black-tipped primaries with large white spots in outermost primaries, forming relatively large white patch at tip of wing. Adult winter (Definitive Basic) plumage differs from Alternate plumage in having heavy grayish-brown mottling and clouding on head and neck, especially hindneck. Eyes (irides) dark amber to dark olive-brown (often darker in breeding condition), but typically entirely pale yellow in ne. Asian breeders, though rarely shown in other populations. Bill entirely yellow to greenish yellow (brightest on breeding birds), typically becoming marked with vague dusky band near tip of bill in winter; legs and feet variable but usually dull grayish green to yellow-green, sometimes tinged pinkish (often brighter and yellower in breeding condition). Sexes similar throughout year. Size, bill shape, eye color, and wing-tip pattern vary geographically (see Systematics, below).

European L. c. canus, which occur casually in winter along the North American north Atlantic Seaboard, are usually more finely spotted on head and neck in Basic plumage than is the Short-billed Gull. All Eurasian populations also differ from Short-billed Gull in having more extensive black on outer 3 primaries, extending to or nearly to primary coverts on outer 2 primaries. Although this difference is best determined on specimens, it may be discerned in flight or on resting birds. On folded wing, Short-billed Gull shows only a narrow black line along outer primary bordered by gray on remaining primaries visible below tertials and behind line of folded secondaries, whereas Eurasian L. canus shows a distinct angle of black from lower edge of tertials forward and down to outer edge of primaries. This feature may not be visible in field depending on bird's posture. Race heinei larger, darker in all plumages and heavier-billed than canus. Adult has yellower bill and legs, the former often with a dark subterminal bar even in summer. Race kamtschatschensis is largest race and darker than canus in all plumages, although dark head markings of winter adult less pronounced than in canus. In adult kamtschatschensis the iris can be pale straw-coloured, mid-brown or dark. (For other differences, see Systematics, below.)

Distinctive subadult plumages occur from first fall through age 2 yr (Juvenile to Alternate II plumages; geographic variation is marked in these plumages). Birds in Basic II similar to adult, with more extensive black on primaries merging with black on primary coverts to form larger black wedge on outer wing (other minor differences include smaller white spots in primaries and greater amount of dusky markings on head and bill). Juvenile plumage heavily mottled with grayish brown, including forehead, becoming almost uniform brownish on lower breast and belly; tertials rather uniformly brownish with pale margins; back, scapulars, and upperwing coverts gray-brown with whitish edging (greater coverts paler overall than smaller coverts, which have rather rounded shape to tip of internal brown patterning); bill dark, with paler pinkish- to yellowish-brown base; underwing coverts almost uniformly grayish brown (only diffusely spotted or checked) and underside of remiges silvery gray with darker tips to primaries. Rump and uppertail coverts white with heavy-brownish mottling or barring; tail appears mostly dark brown with narrow pale tip (sometimes paler grayish-white base of rectrices extensive enough to show beyond tail-coverts, but usually hidden). Fairly well-defined gray mantle (back and scapulars only) acquired by first winter (Basic I), accompanied by slight paling to underparts and grayish-pink base to bill, which usually shows distinct blackish tip (distal third or so). Legs and feet grayish pink.

Juvenile and Basic I European Common Gulls that occur on east coast of North America differ from Short-billed Gull in having sharply defined narrow blackish band at tip of white tail, rump, and uppertail coverts, the latter at most sparsely spotted or barred with dark markings; sparse but distinct brownish tips on whitish underwing coverts; and generally whiter belly with scattered barring and spotting (especially on sides). Kamchatka Gull from ne. Asia most similar to European birds in pattern, although more heavily patterned with relatively coarse, blackish marks and bars on rump and uppertail coverts, more extensively dark tail showing dusky margins to outer webs of rectrices extending basally on dorsal surface (underside appears more distinctly banded, as on European birds); ne. Asian birds also show distinct, though more extensive, dark tips to pale underwing coverts creating a coarsely marked pattern, and more extensively barred and spotted belly. All Eurasian birds in these plumages show a vague dark bar across secondaries and dark outer primaries from below, unlike Short-billed Gull, which lack this bar and are pale silvery gray across underside of remiges except for tips of primaries. Additionally, all Eurasian birds in Juvenile plumage show a pale-whitish area around base of bill and forehead, this area typically streaked brownish on Short-billed Gull; forehead becomes progressively whiter with molt to Basic I, but Eurasian birds usually paler still. First-winter kamtschatschensis has a broader black tailband and second-winter has browner upperwing-coverts, a much darker underwing and a trace of tailband, unlike canus.

Similar Species

Separation of Common Gull from Ring-billed Gull (L. delawarensis) a frequent identification problem. Adult Ring-billed averages slightly larger, with more robust build and has only a narrow white tertial-crescent, paler gray upperparts (beware some European Common Gulls may approach pale gray of Ring-billed), and thicker bill that is rather parallel-sided (profile along culmen and lower mandible) and that has a distinct black subterminal band. Most adult Ring-billed Gulls have quite pale yellow eyes (Common Gull generally has darker eye, except ne. Asian birds); head finely spotted and streaked on Definitive Basic Ring-billed (Short-billed Gull heavily and diffusely mottled on head and neck in Basic plumage, but Eurasian Common Gull is patterned with sparse fine spots and streaks, like Ring-billed). In flight, large white patch formed by 2 large "mirrors" on Common Gull also distinctive from smaller white spots on Ring-billed Gull. Juvenile and Basic I Ring-billed Gulls differ most distinctly from Common Gull in usually showing a variegated tail pattern often with multiple broken bands basal to a broader dark subterminal band (Common Gull has a rather sharply defined dark subterminal band and white tail to rump, a pattern rarely exhibited by Ring-billed). By Basic I, Common Gull typically shows well-defined gray saddle (back and scapulars), whereas Ring-billed often has brownish markings in outer scapulars, disrupting saddle. Common Gull has lesser and median wing coverts more muted grayish brown with less contrasting, rounded brownish internal markings, while Ring-billed shows more strongly contrasting pattern in wing coverts, especially paler panel across greater coverts and prominent arrowhead-shaped and pointed internal pattern on lesser- and median coverts (latter pattern difficult to assess, especially if coverts worn or observer at some distance). In flight, Short-billed Gulls lack contrasting dark bar across secondaries from below shown by first-year Ring-billed, while Common Gulls are similar to Ring-billed in this trait. For details of identification, see 8, 9, 10, 11, and 12 . Excellent depictions and descriptions also appear in several field guides; e.g., 13, 14, 15, and 16 . For separation of Common and Short-billed Gulls, see Identification.

Plumages

Hatchlings

Chicks covered with thick, soft coat of down. European hatchlings described by Fjeldså (17). Prominent black spot on anterior portion of forehead said to be diagnostic for this species among European gulls.

Juvenile Plumage

Both canus group and kamtschatschensis differ from L. brachyrhynchus in that head and neck more extensively streaked with whitish and paler, especially in loral region and forehead; primaries more extensively dark, with outer 4–6 mostly dark (paler inner web not well exposed until primaries inward of these; i.e., P1 to P5–P7); secondaries show through as darker bar from below (vague to prominent vs. almost no bar below on L. brachyrhynchus). L. canus has mostly whitish rump and uppertail coverts with small brown bars (mainly outer margin), extensively white base of rectrices (showing well beyond uppertail coverts), and sharply demarcated blackish tail-band (vs. more brownish tail on brachyrhynchus); outer rectrices, especially, may have black running basally along outer margin, and rare individuals may have dark tail-band up to or just beyond uppertail coverts (pattern and demarcation always distinct, however); underparts much whiter overall compared to brachyrhynchus. Kamtschatschensis group overall similar to canus group, especially in wing pattern, but more extensively dark (toward brachyrhynchus) on body plumage (dark spotting and mottling more extensive and canus but differs from more uniformly dark pattern of brachyrhynchus), and with broader blackish tail band that is still usually rather distinctly demarcated from whitish base, which often is more prominently barred or mottled, especially outermost rectrices; rump and uppertail coverts overall whiter and less heavily barred than brachyrhynchus, but more so than canus group.

Basic I Plumage

Basic I plumage similar to Juvenile plumage except pale mottling and streaking more extensive on head and belly, with throat, portions of breast, vent, and undertail coverts appearing paler. Dark-brown wash on lower neck and sides of breast becomes prominent, and belly usually more or less solidly grayish brown.

Eurasian L. canus paler on rump, uppertail coverts, head, neck, underwing-linings, and belly than L. brachyrhynchus; these areas mostly whitish or indistinctly streaked and mottled on European (L. c. canus) gulls and increasingly marked eastward across Asia. Gray on back and scapulars is paler on European birds, and becomes darker gray in ne. Asia, where darkest (kamtschatschensis) have gray similar to Short-billed Gull.

Alternate I Plumage

Alternate I plumage characterized by more solidly gray back and scapulars contrasting with paler (worn) wing coverts. Head and underparts whiter through molt and wear. Remiges and rectrices as Juvenile, but paler brown from fading and wear.

Basic II Plumage

Basic II plumage characterized by back, scapulars, and wing coverts mostly gray, some wing coverts washed with brown, and uncommonly wing coverts brownish with pale edgings. Head and neck heavily washed with brown or grayish brown, this sometimes extending down flanks; rump and uppertail coverts mostly white; tail white with irregular subterminal black band, most frequently broken in center; this band uncommonly is complete and sharply demarcated, rarely lacking (tail all white), or exceptionally tail appearing all dark as on Basic I (11). Primaries brownish black to black, with outer 2 dark to or nearly to primary coverts and P8 (third from outside) usually showing a noticeable gray tongue on inner web (this gray tongue bordered with small wedge of white before black tip); outermost primary (P10) often with small white subterminal spot (mirror) and, more rarely, (P9) also with smaller white spot. Tips of gray tongues on inner primaries with black tips or subterminal bands (P4–P8) usually have small to medium-sized white wedge bordering gray just inside black tip. Primaries may have, at most, a very small white apical spot, but this usually lacking, especially on outer primaries. Secondaries gray with moderately broad white tip. Primary-coverts gray to gray brown with variable blackish tips, these running in short point basally. Lower (posterior) scapulars gray with narrow white tips. Tertials gray with broad white tips. Underparts white.

Alternate II Plumage

Head and body mostly white. Dark areas of wing faded and worn, white areas usually worn away. Wing-coverts more extensively gray (but this may be because of overlap with onset of Definitive Prebasic molt).

Definitive Basic Plumage

Described in Identification and Similar Species.

Definitive Alternate Plumage

Definitive Alternate plumage similar to Definitive Basic except head and neck become entirely white.

Molts

Similar to Short-billed Gull (which see), on which most descriptions of plumages are based.

Bare Parts

Colors vary with age and season (winter or summer, and whether in breeding or nonbreeding condition). Descriptions from sources listed under Molts and plumages, above.

Bill And Gape

Nonbreeding (Basic) adult bill dull greenish yellow, typically with basal portion more greenish (from gonydeal angle); variable subterminal dusky mark or band on bill typically noticeable. Breeding (Alternate) adult bill yellow to greenish yellow throughout, color brighter and more vivid than nonbreeding; gape becomes bright pink to red (vermilion), and inside of mouth orange.

Juvenile bill blackish with dull grayish pink base, this color becoming more extensive into Basic I and only tip black (about distal one-third, from near gonydeal angle to tip); line demarcating black irregular and often extending basally along cutting edges of mandibles from angle, and extreme tip sometimes pale. Gape ochraceous. From mid- to late winter, pinkish base changes to yellowish pink or pale olive-gray as bird acquires Alternate I, when gape becomes pale orange-buff. Basic II bill grayish blue-green with black tip.

Iris And Orbital Ring

Iris typically dull yellowish brown to greenish yellow, appearing rather dark, especially at a distance, and varying from dull yellow to dark brown; occasionally quite pale-eyed birds occur, with lighter and clearer coloration (fewer dark fleckings in iris); these may have light grayish-yellow irides. Orbital ring of breeding adult red (vermilion); orbital ring on nonbreeding birds hardly noticeable and dark (black or brown).

Juvenile and Basic I irides dark, brown (raw umber or Prout's brown) to grayish brown. By Alternate I, iris may begin to lighten somewhat (Verona brown in 18). Basic II iris nearing that of Definitive adult, but averaging darker (brown, buffy, or burnt umber; 18).

Legs And Feet

Definitive Alternate birds have greenish-yellow legs and feet; in winter, Definitive Basic birds have duller, more greenish to grayish-green legs and feet.

Juvenile has dark pinkish-brown legs and feet, these becoming more pinkish into first Basic and dull grayish pink, bluish pink, or grayish blue-green, sometimes with yellow tinge, in Basic II.

Measurements

Linear Measurements

See Appendix 1 In Scotland, males significantly larger than females in 2 dimensions: bill + head length and wing length. If bill + head >87 mm, 95% probability is male; if bill + head <87.4 mm, 95% probability is female (J. C. A. 19).

Mass

See Appendix 2 . Males significantly heavier than females in all locations. In Norway, masses of males increase south to north, while those of females same at all latitudes (20). No data on seasonal change in mass, but females probably heavier near egg-laying.

Systematics History

Long generally considered conspecific with Short-billed Gull Larus brachyrhynchus, as Mew Gull Larus canus, and only formally split very recently (21). Although all are clearly closely related, a genetic study suggests that Short-billed Gull is more closely related to Ring-billed Gull than to the Palearctic members of L. canus (22); and morphological and vocalization differences have been analyzed quantitatively (23), bolstering the argument that Short-billed Gull differs at the level of species.

Major groups of Larus canus sensu stricto include: European and central Asian breeders (canus group), the name Mew Gull sometimes restricted to these populations; and ne. Asian breeders (kamtschatschensis), often called "Kamchatka Gull". However, the name "Mew Gull" has been used confusingly, with most North American literature using it for the species as a whole. In the past, and to some extent recently, "Mew Gull" has been used for European birds only (canus group), with Short-billed Gull used for North American L. brachyrhynchus (e.g., 24, 25), and the latter name has now been reinstated for L. brachyrhynchus (21). Likewise, the name "Common Gull" has been applied confusingly at times, with English literature in Europe generally using this name to refer to the species as a whole, but many popular North American accounts and field guides using it to refer to European birds of the canus group. In this account, Common Gull is used for the Eurasian species L. canus sensu stricto, with Kamchatka Gull being used for the kamtschatschensis group.

Species limits within the Common Gull remain uncertain, now mainly whether to recognize 1 or 2 species across Eurasia, which requires further study. Although "Kamchatka Gull" (L. c. kamtschatschensis) differs in a number of morphological characters (size, plumage pattern, eye color) from the canus group, it appears to be the end point of more or less clinal variation in these characters across Europe and Asia. While some authors have noted that many characteristics of "Kamchatka Gull" appear intermediate to Short-billed Gull (e.g., darkness of gray mantle and heavy mottling in Juvenile and Basic I plumages; 26), others have recognized "Kamchatka Gull" as a separate species while considering Short-billed and Common (canus group) gulls as a single species (27). Despite these opinions, morphological evidence suggests that it is best to consider all Eurasian taxa as more closely related apart from L. brachyrhynchus. Within Eurasia, individuals that appear intermediate between L. c. kamtschatschensis and the canus group (through subspecies L. c. heinei) are known from about the Lena River region east to the Indigirka and Kolyma Rivers in ne. Asia (28, 29; specimens in Zoological Museum of Moscow, according to Devillers [30]). This apparent intergradation along with overall similarity in wing pattern of adults (e.g., extensive black in outer 3 primaries) and several plumage characteristics of Juvenile and Basic I plumages (bold dark tips to whitish underwing coverts, dark bar across underside of secondaries, underside of primaries, whitish pattern around base of bill and forehead on Juvenile) suggests all Eurasian taxa are more closely allied than is L. brachyrhynchus. Indeed, 2 species were recognized along these lines (Eurasian vs. North American) by Sibley (31), who based this chiefly on limited genetic comparisons by Zink et al. (32). Overall, the most dramatic difference in size and appearance is between L. c. kamtschatschensis and L. brachyrhynchus. Using restriction fragment length polymorphisms (RFLP) to compare the mitochondrial DNA of these taxa (1 specimen from Kamchatka and 2 from Washington), Zink et al. (32) found L. c. kamtschatschensis and L. brachyrhynchus highly differentiated relative to other avian taxa (percentage nucleotide divergence, p = 0.02). Further comparison of genetic samples across Eurasia (especially in zone of intergradation between L. c. kamtschatschensis and L. c. heinei) as well as between North American and European (L. brachyrhynchus vs. L. c. canus) are needed to better understand their evolutionary relationships.

Geographic Variation

The following is based on 28, 33, 34, and examination of specimens at Museum of Comparative Zoology (MCZ) by LRB. Size increases more or less clinally from west to east across Eurasia, with birds breeding in ne. Siberia being largest, having proportionately larger bills and consistently pale yellow irides. On adults, wing-tip pattern and mantle color all vary geographically. Mantle color apparently palest in w. Europe and Iceland, becoming darker gray eastward across Eurasia, with darkest in central and e. Asia. Reported differences in darkness of mantle in the literature are conflicting, however. For example, Dement'ev and Gladkov (28) state that e. Siberian populations (L. c. kamtschatschensis) are darkest in Eurasia, being darker than those populations immediately to the west (L. c. heinei); Johansen (27), however, reported that L. c. kamtschatschensis and L. c. heinei were most similar. Size and distribution of white markings in wing-tips, and differences in extent of gray and white borders to black primary-tips exist, with ne. Asian birds similar to North American Short-billed Gull in showing a band of white spots between black wingtip and gray wing, but typically lacking a white spot between gray and black on P8; European birds usually lack any white between gray and black of primaries, but may rarely show narrow white markings there. In addition to size and structure, differences in plumage pattern exist in all Predefinitive (subadult) plumages among the subspecies groups.

Subspecies

Three subspecies.


EBIRD GROUP (MONOTYPIC)

Common Gull (European) Larus canus canus Scientific name definitions

Systematics History

L. c. canus Linnaeus, 1758; type locality restricted to Sweden.

Distribution

Breeds Iceland and British Isles east to White Sea, Russia; winters across Europe to n. Africa east to Persian Gulf; rare in winter (Sep-May) along Atlantic Seaboard, with a few summering records in recent years from Quebec attributed to this race. Specimens of L. c. canus have been taken in Greenland and Massachusetts (35, 36). Occurrence along Atlantic coast of North America also supported by many sight reports supported with identifiable photographs showing characters of this subspecies; most records are from Newfoundland and e. Quebec (B. Mactavish unpubl., Quebec regional summaries in North American Birds and predecessors), whereas scattered records exist from Nova Scotia, New Brunswick, Maine, Massachusetts, New York, Maryland, Virginia, and N. Carolina (37, 35, 38, LRB). One specimen, from Lock's Cove, Newfoundland, 19 Apr 1956 was of a bird banded as a chick on the White Sea (37); another individual banded as a chick in Iceland returned to Newfoundland for at least 6 winters (B. Mactavish pers. comm.). So far, all North American records identifiable as L. c. canus are from the immediate coastal region, but with increasing populations in Iceland and consequent increase in records in recent decades along the east coast, records from farther inland in e. North America might be expected.

Identification

Medium size, similar to L. brachyrhynchus but perhaps slightly heavier and with slightly bigger bill; adult has black extending to near tips of primary coverts on P8-P9; usually lacks white spot between gray and black on primaries, although this highly variable, and many specimens show some small white spots similar to L. brachyrhynchus (LRB); mantle medium to pale gray, with w. European birds averaging paler than L. brachyrhynchus (some almost as pale as Ring-billed Gull); eye generally dark (averages darker than L. brachyrhynchus).


EBIRD GROUP (MONOTYPIC)

Common Gull (Russian) Larus canus heinei Scientific name definitions

Systematics History

L. c. heinei Homeyer, 1853; type locality based on wintering bird from Greece (synonyms L. c. var. major Middendorff and L. c. stegmanni Brodkorb).

Distribution

Breeds across a vast region from central Russia (Kanin Peninsula and Moscow region) east to w. and central Siberia (Lena River); winters Baltic Sea, se. Europe, Black and Caspian Seas, Persian Gulf, and, to lesser extent, e. Mediterranean basin, n. Red Sea, and perhaps also se. China. Diagnosability of this taxon from L. c. canus needs to be reexamined; many birds not certainly identifiable (e.g., see 30). Birds showing wing characters of this subspecies reported over 1,200 km east of Lena River on Omolon River (10).

Identification

Similar to L. c. canus, but averages larger and darker on mantle; tends to be whiter-headed in Basic plumages, being more sparsely marked on head and neck; intermediates with L. c. canus frequent in Israel (39).


EBIRD GROUP (MONOTYPIC)

Common Gull (Kamchatka) Larus canus kamtschatschensis Scientific name definitions

Systematics History

L. c. kamtschatschensis (Bonaparte, 1857); substitute name for Gavina Kamtchatchensis Bonaparte, 1854; type locality Kamchatka.

Distribution

Breeds ne. Siberia from Lena River east to Anadyrland and Koryakland, south to Sakhalin, Kamchatka, and Kuril Is.; winters coastal e. Asia (China, Taiwan, Japan, and islands south of Japan). Vagrant to w. Aleutians (Attu, Shemya), St. Lawrence I., and Pribilof Is. (St. Paul), based on photographs and specimens (40). Other reports along west coast of North America remain uncertain.

Identification

Largest subspecies, with relatively more robust bill that is thicker and more parallel-sided than other races; black extends basally to near tips of primary coverts on P8-P9; P1-P7 usually with white spot between gray and black; mantle medium gray; eye generally pale yellow.

Related Species

Most authorities consider Ring-billed and "Mew" (Common and Short-billed) gulls closely allied, based on comparisons of morphology and behavior (e.g., 18, 41, 42, 43). Based on phylogenetic analysis of mitochondrial DNA sequence data, Mew Gull emerges basally with Ring-billed Gull in a clade of "white-headed" Larus species, the relationships of which are otherwise unresolved due to apparently rapid radiation (44, 22).

Hybridization

Individuals thought to be hybrids between Common Gull (Larus c. canus) and both Black-headed Gull (L. ridibundus) and Mediterranean Gull (L. melanocephalus) have been reported and photographed in w. Europe (45, 46, 47).

Distribution

Breeding Range

Iceland eastward across Eurasia, from Faeroe Is., British Isles, Scandinavia, and n. Russia east to ne. Siberia (Anadyr and Koryakland), and south to central Europe (Netherlands and n. Germany); east generally north of 55°N along Volga River, Kirghiz Steppes, Minusinsk, Lake Baikal, n. Mongolia, sw. Siberia (Stanovoy Mtns.), and Sea of Okhotsk from Kamchatka and Kuril Is. south to Sakhalin; isolated breeding on lakes in Armenia, nw. Iran, and perhaps Caspian Sea (28, 29, 34).

Winter Range

From breeding range south to Iberian peninsula, Mediterranean region, n. Africa, Israel, Iraq, Persian Gulf, Black and Caspian Seas, Afghanistan, Pakistan (rare); also coastal e. Asia from Japan and Korea south to se. China and Taiwan (29, 34, 39). Some breeding populations move little (e.g., present all year in Faeroe Is. and s. Baltic Sea). Those breeding in Finland winter from Denmark to Britain , while other European birds winter from the Baltic to Brittany. Relatively few reach the Mediterranean ; up to a few hundred occur in the Iberian Peninsula in winter, where most are found on N coast, hardly any reaching the far S (48). A few, mainly first-winters, reach the Moroccan Atlantic coast in winter 49. E Siberian birds (kamtschatschensis) winter from S Ussuriland coast and S Japan to SE Asia, with a recent record from the Philippines (Luzon, Dec 2013–Jan 2014) (50). C Russian breeders (heinei) winter in the Baltic, Black and Caspian Seas and in Middle East, some moving to S Asia; some of this race winter in C Europe.

Summer Nonbreeders

No information.

Other Records

Accidental in Pacific Ocean to w. Hawaiian Is. (Kure) and possibly Palau; also sw. Bering Sea to Commander Is. (51, 52). Casual to Greenland (36) and accidental to Spitsbergen and Bear I.; also casual south in e. Atlantic to Azores, Madeira, Canary Is., and Mauritania (34); and vagrant to Nepal, Bhutan, India, and Pakistan (53, 54, 55).

Historical Changes to the Distribution

European range and population increased over last few decades; Iceland colonized in 1955, with population there apparently expanding rapidly (e.g., 60 pairs in early 1980s and 300–400 pairs by end of that decade; 34, 56). Records of European-origin birds along Atlantic Seaboard of North America likewise have increased over past several decades.

Habitat

Coasts, tidal estuaries, agricultural land, reservoirs; breeds on coastal cliffs and islands, in beaches, bogs, marshes and meadows, not necessarily close to wetlands.

Habitat in Breeding Range

A remarkably adaptable species; breeds in both marine and freshwater habitats. In w. Palearctic, as likely to be found on sea coasts or inland either near or at a distance from water. Mostly in lowland areas, but found up to 900 m in Scotland and to 1,400 m in Norway. Most nest sites near lakes, pools, in bogs, or grassy or heather moorland, on open ground away from water, and cultivated grain fields. On marine coast, breeding habitat varied: small inshore rocky stacks, islets and islands, grassy and rocky slopes, sand dunes, and the foreshore. Uses shingle bars, stony islets, and marshes on rivers (34; see Breeding: nest sites, below). In Poland, colonies use sand bars without vegetation about half the time, the rest divided between different vegetation types: dispersed dwarf herbs (15.0%), dispersed willow (Salix spp.) bushes (17.4%), and thickets of tall willows, tall herbs, or steep banks (20.4%; n = 314 colonies; 4). Across Eurasia, chiefly associated with lakes and large rivers; in Kamchatka, L. c. kamtschatschensis nests on rivers, marshes, tundra, and islands in lakes (28).

Habitat in Nonbreeding Range

Habitat in the Overwintering Range

In most areas, habitat during migration and winter is similar, with birds associated with nearshore waters and coasts, river estuaries, beaches, mudflats, harbors, and sewage outfalls and treatment ponds. Shortly after breeding, European birds shift to grassland and croplands as well as tidal estuaries; winters more often along seacoasts and harbors at southern limits (34).

Movement

Short- to medium-distance, mostly complete migrant. Breeding populations in ne. Asia winter from coast of s. Ussiriland in Russian Far East and Sea of Japan south to se. Asia. Most breeding birds of central Russia migrate to Baltic, Black, and Caspian Seas and Middle East, some to s. Asia. Race canus is least migratory, many moving relatively short distances and others being sedentary. Birds breeding in Finland migrate only as far as Britain and Denmark. Other European populations winter from the Baltic to Brittany, with some reaching Mediterranean (57).

Dispersal and Site Fidelity

Fidelity To Breeding Site

Site fidelity strong, with up to 90% of pairs returning to same site every year (34). In the Netherlands, >50% of banded birds were found within 40 km of where they were originally banded. Site fidelity of younger birds is higher than that of older birds (58). In Estonia, only 5% of pairs in 25-yr study changed nesting islands between breeding attempts, usually young pairs; 41% of males and 4% of females bred in the natal colony (6). On Vistula River in Poland, 50% of colony sites used in 1981 were used in 1982. Turnover rate a function of colony size: rate for small colonies (1-5 pairs) 40-49%, that for large colonies 5-10% (4).

Timing and Routes of Migration

Spring

L. c. canus group begins departure from southernmost wintering areas Feb to late Mar (mostly in second half of Feb and early Mar in Israel; 39), peaking during mid Mar to mid Apr for adults, and late Apr to mid May for first-years (59) . In Europe, pattern is for migration to take place through maritime countries; however, numbers in central Europe have been increasing (34). In sw. Finland, alters spring migration schedule (1989-1991) when ice breaks up early; individual adults occupying breeding colonies 26 d earlier than late springs (60). In Japan, L. c. kamtschatschensis gone by early May (61).

Fall

Adults leave earlier than juveniles. In S Scandinavia two main migratory waves are observable; the first involves Fennoscandian and Baltic breeders and begins in mid Jun with second-years, adults peaking mid Jul to early Oct and juveniles in Sept–Oct. The second peak probably involves adult Russian breeders, including some heinei, and peaks during late Oct to mid Nov. Most birds arrive in Baltic and North Sea Aug-Sep; arrival at southernmost wintering localities dependent on severity of winter (e.g., most south to Brittany in west, reaching Iberian peninsula and Mediterranean in coldest winters) and gradual, with birds arriving from late Oct to mid-Jan, most arriving in Israel mid-Nov (34, 39). Large-scale coastal movements are observed locally during passage periods. Large migrant roosts, of tens of 1000s of birds, occur in autumn, notably in Denmark and Netherlands 59. Arrives in n. Japan ( kamtschatschensis group) at Hokkaido by late Sep and is common on coasts until late Dec, withdrawing as snow and ice appears; occurs in central Honshu from mid-Oct to early Apr, and has occurred as far south as Okinawa in Jan and Feb (61).

Migratory Behavior

No information.

Control and Physiology of Migration

No information.

Feeding

Main Foods Taken

Omnivorous . In Europe, mainly terrestrial foods, earthworms, insects, grain, garbage; less so fish and invertebrates (62). On White Sea coast, however, diet largely dependent on the sea (63).

Microhabitat For Foraging

Varies with type of food consumed. In Europe, uses 3 habitats: wet field, 53%; mudflat, 26%; and river marsh, 21% (64). In Scotland and Norway, of 8 possible substrates, 2 dominant: inland fields, 74.6%, and water (open sea), 15.2% (65). In Wadden Sea, Netherlands, feeds on exposed tidal flats and at tide line (66). Pursues mixed foraging strategy in France that begins in water then moves into fields and meadows of interior before returning to water to roost, particularly in winter, when days are short. Several factors determine whether foraging is at littoral only, interior only, or is mix of water and inland feeding: age of bird, amount of time between sunrise and the next high tide, and whether there are temporary ponds on agricultural lands (67). In United Kingdom, in winter, 93.4% feed in fields (68). A comparative study of a coastal North Sea breeding colony found that this species and L. ridibundus divided their foraging between the intertidal zone and terrestrial habitats, and both were scarce at sea (69).

Food Capture And Consumption

Multiple techniques to obtain food: Occasionally kleptoparasitic, sometimes uses aerial foraging; some swim-dipping and surface-dipping observed. Flutters over water, head down, and legs dangling to pick up bits of food from water surface. Sometimes paddles against current, picking up food as it floats past. Intentionally drops mollusks onto hard surfaces in flight (57). Difference in diet and foraging habitat between North America and European populations leads to differences in foraging methods (see Diet, below). As a percent of total, in North America, pick up, 29%; surface dip, 32%; jump plunge, 20%; and aerial dip, 19%; in Europe, pick up, 79%; surface dip, 21% (64).

Kleptoparasitizes several species in multiple habitats, at times defending a robbing area against other gulls (70). Kleptoparasitizes earthworms from Northern Lapwing (Vanellus vanellus), European Golden-Plover (Pluvialis apricaria), and Common Redshank (Tringa totanus) in pastures (71). Kleptoparasitizes Eurasian Oystercatcher (Haematopus ostralegus) feeding on common cockles (Cerastoderma edule), mostly when cockles are larger. Success rate of attacks without flight (unknown) greater than attempts to steal prey after a flight (36%). Kleptoparasitism most profitable when prey is large (72). Kleptoparasitizes Eurasian Curlew (Numenius arquata) and Bar-tailed Godwit (Limosa lapponica; 71). At a garbage dump in Ireland, rather than eating refuse, apparently obtained all its food by kleptoparasitizing Black-headed Gulls that were foraging in dump and often carried away sizable food items that are difficult to swallow at once. In a nearby pond, if a Black-headed Gull was on water, Common Gull swooped down and, after settling on water, attempted to steal prey item; if in the air, it was pursued until it surrendered food (73). In n. Norway, successful in 25-75% of attacks on Bar-tailed Godwits, which may lose 20-25% of the worms they catch (70). In competition with other seabirds following fishing vessels and scavenging in the North Sea, steals 1.2 fish for every fish stolen from it (74). Reduced availability of primary prey species in Oct on Wadden Sea leads to higher rate of kleptoparasitism (66).

Steals eggs from Eurasian Golden-Plover nests in ne. Scotland and Eurasian Oystercatcher nests in Netherlands, mainly when clutch is completed (75, 76). In fishing for river lamprey (Lampetra fluviatilis), circles several meters above water. Upon sighting prey, dives to surface of water to capture fish. If successful, immediately leaves area with lamprey in its bill to avoid being kleptoparasitized (77). Follows commercial brown shrimp (Penaeus aztecus) trawlers in E. Frisian part of Wadden Sea (78). In a North Sea experiment in which roundfish and flatfish were discarded, however, one of the least successful species attempting to feed on discarded fish. This may account for it being an infrequent ship follower (79). In Wales follows mechanical harvesters of cockles scavenging harvested areas for annelids, thin-shelled mollusks, and smaller cockles (80). Inland, also follows plough, feeds on new-mown fields.

In winter, where they eat larvae of winter moth (Operophtera brumata) and dotted border (Agriopis marginaria) off heather (Calluna vulgaris), individuals feed by balancing on heather plants, frequently fluttering as they feed, and walking slowly, pecking at rate of 1/s (81).

Diet

Major Foods Items

Diet varies by location and season. In Europe, insects 75%, offal 25% (64).

Geographic Differences

In e.-central England, birds foraging in fields eat earthworms, fly larvae (Tipulidae and Chironomidae), beetles (Staphylinidae, Carabidae, Lathriidae, Phalacridae, and Helophoridae; 82). In w. Siberia from 1963 to 1971, mammals in 68.3% of droppings, insects in 41.8%, fish in 14.9%, birds and bird eggs in 12.2%, and plants in 17.2%, but interyear variation in diet extraordinary: mammals in 37.1% of droppings in 1967, 82% in 1970; insects in 7.4% of droppings in 1968, 31.4% in 1971 (83). Regularly feeds on roadkill in Shetland, especially Old World rabbit (Oryctolagus cuniculus) and hedgehog (Erinaceus europaeus; 84). In sw. Sweden, birds breeding near mainland consume some fish and marine invertebrates, but mainly eat insects, earthworms, and grain on inland fields (85). On island of Heligoland, Sweden, stomach contents (n = 93): 82.7% garbage and 17.3% natural food (e.g., Crustacea, Mollusca, Insecta), of which 37.6% stomachs contained fish, principally poor cod (Trisopterus minutus), cod (Gadus morhua), and whiting (Merlangius merlangus), and 33.3% contained pieces of plants (86). In Baltic, diet consisted of 73% fish.

Seasonal Differences

Sharp intermonthly shifts in diet in nw. Russia near White Sea: from May to Sep, insects 6.1-31.1% of diet; cereal seeds, 18.9-46.5%; vegetation, 3.2-20.2%; scuds, 27.1-61.1% (87).

In Wadden Sea, consumed green crabs (Carcinus maenas) and sandworms (Nereis diversicolor) in Sep and Oct and then switched to fish, mussels, and other polychaetes (66). On Finnish coast in early summer, eats large amounts of the pine weevil (Hylobius abietis); when weather turns cold in fall, switches mainly to oats (Avena sativa), but also corn (Zea mays) and other plant matter (88). Seasonal and daily activity foraging patterns connected to those of river lamprey in n. Sweden. River fish present in diet only during breeding season. Peak of nocturnal feeding of birds coincides with peak of spawning period; during summer solstice, foraging activity lasts 24 h (77).

Idiosyncratically forages on cherries (Prunus spp.) and other fruit in Germany and Scotland (89, 90). Those eating cherries in Scotland were 76% juveniles, although only 37% of flock were juveniles. Shift to fruit may have reflected absence of usual diet of earthworms because of exceptionally dry weather (90).

Food Selection and Storage

No information.

Nutrition and Energetics

No information.

Metabolism and Temperature Regulation

No information.

Drinking, Pellet-Casting, and Defecation

No information.

Vocalizations

Vocal mainly in breeding season.

Development

No information.

Vocal Array

Calls of Eurasian birds described as piercing keeaa-keeaa or chak-chak (91), with possibly lower and hollower quality than North American birds (16), and more prolonged, flatter-shaped long call notes than the symmetrical ^-shaped notes of the corresponding call of L. brachyrhynchus (23). Long call of L. c. canus described as KI-a kia kiiiija ka-ka-ka-ka-ka-ka-ka-ka-ka-ka (34). Variations depend on motivational state of individual bird. Detailed description of various calls of L. c. canus based on study in gull colony on small island in Loch Sunart, Scotland, as follows: Long Call is several short, low-pitched notes followed by 2 or 3 very high, long, loud, and harsh screeches, followed by 2 or 3 gradually descending lower-pitched notes. Long Call accompanies the Oblique Posture (see Behavior: agonistic behavior, below). Frequently, a brief guo or gliie is incessantly repeated at brief intervals. Two gulls can exchange Long Calls for several minutes at a time. Long Call usually used as response of a territory owner when conspecifics fly nearby, or land or walk on or near owner's territory. Crooning Call, which often accompanies the Flat Posture (see Behavior: agonistic behavior, below), is a high, soft oiiiiiiiie lasting 1–3 s and often repeated at intervals. Frequently alternates with scraping during nest-building. May be employed by a pair after landing on its own territory while walking toward nest. Landing Call, associated with Landing Posture, is a rapidly given, short series of loud notes of 4–10 syllables lasting about 1 s that descends midway through a gi-gi-gi-ge-go-gu . This call, given by both sexes, ceases the moment a bird lands on ground. Most often uttered in early morning the first few times birds land on their territories. Copulation Call, given prior to male's attempt to mount female, is a series of loud, deep calls, ga-ga-ga, reminiscent of a cackling hen. Typically, 3 or 4 ga sounds/s, rising in pitch when male mounts female (1).

Geographic Variation

Some apparent differences in vocalizations noted between L. c. canus and L. c. kamtschatschensis (23) may help elucidate their taxonomic status, but require further study.

Social Context

See above. Young recognize parental vocalizations (92).

Nonvocal Sounds

None known.

Locomotion

Walking

Compared with larger "white-headed" gulls, has somewhat dainty gait (26).

Flight

Strong and direct when moving long distances. While foraging, exhibits rather buoyant flight, with fluttering and dipping reminiscent of Bonaparte's Gull.

Swimming And Diving

Often forages on water in manner similar to phalarope (Phalaropus spp.), spinning and dipping, snapping surface of water with bill to capture small prey. Birds on water tend to float rather high with rear (wings and tail) pointing upward and head and neck erect. Dives as part of play behavior (93; see Social and interspecific behavior, below).

Self-Maintenance

Preening

During hailstorms in Great Britain, feeding flocks faced into wind, aligning their bills in direction of hail. Preens followed end of storm (94).

Sleeping, Roosting, Sunbathing

No information.

Agonistic Behavior

Intrapair aggression nonexistent.

Physical Interactions

Fight over ownership of territory, either directly on claimed territory or at common boundary of disputed territory. Fights begin with attacking bird approaching adversary in different ways. May move very near to other in Upright Posture. After threats in one of the postures (see below), may "Dash" or fly at adversary from 2 to 3 m away or may approach adversary quickly in Flat Posture, then attack quickly or perform threat display prior to attack. In the Dash, bill is pointed down and forward, ready for fierce peck. Wings are out of pockets, and attacker may fly a short distance just above ground. Fight begins with a peck. This may end the fight, but attacked bird often fights back, trying to grab attacker's bill, neck, wing, or back. If one has the other in a grip, it will beat its opponent with its wings. Fights can last up to 5 min. Intensity of fight determined by seriousness of intruder's intentions. Casual intruders never wait for second peck and escape immediately after first peck; most escape even before first peck (1).

In winter, adults generally dominant over juveniles (95). Plunge-diving for leaves with Black-headed Gulls appearing to start out as play turns into frequent interspecific aggressive interactions; entire episodes last 10-15 min, followed by bathing (96). Part of flock of 20 conspecifics and Herring Gulls (L. argentatus) harassing a Eurasian Sparrowhawk (Accipiter nisus), repeatedly forcing it to land in the sea (97).

Communicative Interactions

Threat Displays. The following is drawn from 1. Variety of hostile postures against conspecifics. Upright Threat Posture most frequently employed by territorial male against intrusion; females alone on a territory will also assume the posture. Rarely used in boundary disputes with established neighbors, however. Head stretched upward and somewhat forward and distinctly pointed down; neck swollen. Outcomes suggest that purpose of posture is to convince another individual to escape and render chasing and fighting unnecessary.

In Anxiety Upright Posture, neck again stretched and forward, but bill pointed horizontally. Repetitious head and neck movements in several directions suggest anxiety. Occurs when landing on another's territory. Strong tendency to escape when individual invokes this posture.

Oblique Posture, which accompanies Long Call, occurs when neck stretched forward and somewhat upward and bill opened widely when uttering calls. Individual thereby displays distinct vermilion coloration inside its mouth.

In Choking Posture, front of body lowered so that breast touches ground and tail lifted into air. In addition, wings typically out of their pockets; bill, which is closed, pointed downward; and neck somewhat stretched. Head and bill at times moved up and down at a rapid rate. Choking gull either stays in one place or moves forward or sideways slowly toward its adversary. Adversaries usually Choke side by side, often touching each other with sides of their bodies. Choking occurs mostly in boundary disputes between neighbors.

Flat Posture: Body flat, tail possibly raised, neck slightly extended forward, and bill and head held downward. In this posture, will often rush or walk toward an intruding neighbor in hostile encounters. Forward Posture resembles Hunched Posture, but neck slightly extended and held in manner such that there is modest downward curve from body to upper side of neck. Used by intruders when first alighting in another bird's territory.

Head-Flagging, used when bird is in Upright Posture, involves moving head jerkily away from an opponent and then bringing it back slowly to original position. Used under several circumstances, including after copulation, when alighting near mate, or when approaching an adversary.

Appeasement Displays. Possible that Head-Flagging may be gesture of appeasement, as bird removes its principal weapon, the bill, from sight of an adversary (1).

Spacing

Territoriality

Unmated males and pairs chase and threaten intruders off their territory by variety of threat movements and calls. Boundary disputes common; fighting can be intense if both pairs claim an area when the other pair has temporarily left a territory (1; see Agonistic behavior and Sounds: vocalizations, above). Combination of aggressive nature and sizable territory allow it to successfully chase intruders from territory (34).

Individual Distance

No information.

Sexual Behavior

Mating System And Sex Ratio

Typically monogamous.

Pair Bond

Pair bonds sometimes maintained for many years. In Estonia, 72% of pair bonds maintained in succeeding breeding seasons (34). Thus, some birds are already paired when they arrive at the colony (2). Bigamous males rare; in such cases, both females lay eggs in same nest and all 3 defend territory (34).

Courtship Displays and Mate-Guarding. Hunched Posture used only by females in early stages of approaching male. Neck retracted, thus looking thick, bill and body both held horizontally. Female walks around male in this posture while Food-Begging. Both sexes can Food-Beg, repeatedly tossing up bill. Begging bouts can last from one "beg" to 2 min of failed begging by female (1). Pair-bonding begins when female approaches territorial male in Hunched Posture. After Head-Flagging, female begs for food. Already-paired male chases female away. Unmated males also aggressive, but may follow female that flies too far away; alternatively, females may return to pursue male. Pair bonds develop over time, after which aggression ceases. One mate, frequently followed by the other, runs toward nest in Flat Posture, giving Crooning Call; pair may then Choke together and perform Long-Call Display or Courtship-Feed and copulate. In Courtship-Feeding, female starts by Head-Tossing. Both sexes then Head-Toss; 4-8 tosses given in 6 s and bill may become vertical. Female moves around male or pecks at his bill until fed. Female most likely to beg after lengthy absence of male. Begging frequently leads to copulation (1, 34).

Long-Call Display. Performed for purpose of territorial defense and during agonistic encounters at feeding areas. Neck stretched forward and somewhat upward, bill slightly open and horizontal. The first go notes of Long Call follow. Then neck is arched in downward direction and long goiiie notes given. Head thrown up to vertical and rest of Long-Call notes uttered with bill wide open as head simultaneously begins to retract into shoulders; carpal joints held outside body throughout this display (34).

Copulation. Copulation Call accompanies act (see Sounds: vocalizations, above). Prior to male mounting female, he extends neck; he then flies onto female's back and uses open, beating wings to balance himself. Bill pointed downward, belly feathers fluffed, male uses claws to grab hold of female's humeri. Then bends his legs until he appears to be sitting. Male lowers tail, and copulation movements begin until cloacas meet. Female often utters Food-Begging Call while male copulates; or is silent but pecks at male's breast (1).

Extra-Pair Mating Behavior

In Poland, extra-pair copulations (EPCs) mainly forced; 15.7% of all copulations, but only 3.6% of chicks (2 of 55) resulted from EPCs, suggesting possible mechanisms for paternity control by mated males and/or females (98).

Social and Interspecific Behavior

Degree Of Sociality

Facultatively colonial (99). In Europe, mostly a colonial nester in both freshwater and marine environments (100). A small number in n. Sweden were solitary nesters (85).

In Europe, extraordinary variation in colony size. In Britain, a few dozen to 300 pairs; in Germany 1,000-2,000 pairs; as high as 10,000 pairs in w. Baltic (34). On Gulf of Finland, breeds in large colonies only when food is plentiful (99). In Poland, on the middle of Vistula River, colony size 1-500 pairs; >50% of colonies 1-5 pairs, although almost 50% of population nested in colonies of >50 pairs, these constituting 6.2% of all colonies (4).

In Ireland, during main breeding period, colonies made up only of breeding birds; second-summer birds quickly chased out of colony (2).

Site tenacity lower in colonies, although colonies tend to be stable. In Sweden, colonial breeders experience lower nest predation than solitary nesters.

Highly gregarious in Europe; flocks up to 100 individuals, although size dependent on habitat. Although roosts with other Laridae, mainly feeds in single-species flocks (34).

Play

Adults dive into shallow water to bring leaves to surface, then shake their heads, repeatedly tossing leaves and retrieving them, or dive after more leaves. Also bring leaf litter to surface, occasionally behaving in a frenzied fashion, diving over and over again and chasing other gulls with leaves until latter are discarded (93).

An immature Common Gull was seen carrying an object to a height of about 10 m, dropping it and then snaring it before it hit water. If object was not caught, it was retrieved from water and behavior repeated. This action was repeated 20-30 times. Three conspecifics joined in activity, and the 4 engaged in dropping and capturing the falling object (101).

Nonpredatory Interspecific Interactions

Forages and nests in association with other species. Frequently joins flocks of Northern Lapwings and European Golden-Plovers and feeds kleptoparasitically (71). In e.-central England, associates with Brant (Branta b. bernicla) in fields of winter wheat (Triticum sp.), feeding on invertebrates disturbed by geese; 86% of gulls feed walking interspersed among geese, remainder searching for food while flying low over geese (82). Nests in association with Parasitic Jaegers (Stercorarius parasiticus) in n. Norway and Common Eiders (Somateria m. mollissima) on west coast of Sweden (102, 103). Association with jaegers likely serves as protection against avian and mammalian predators; association with eiders may help protect latter (102, 104). A single pair nested successfully with a colony of Black-headed Gulls in France and on a roof in Aberdeen, Scotland, with a pair of Eurasian Oystercatchers (105, 106). Member of a multispecies gull roost including Herring, Black-headed, and single Lesser Black-backed (Larus fuscus) and Great Black-backed (L. marinus) gulls in Lithuania (107).

Hybridization. Possibly in Europe based on existence of putative hybrids (see Systematics: related species, above).

Predation

Egg And Chick

Endangered by avian and terrestrial predators throughout its range. In Europe, terrestrial predators are wild boar, badgers, foxes, less commonly wolves, and raccoon dog (Nyctereutes procyonides; 99). Avian predators are Marsh Harrier (Circus aeruginosus), Herring Gull, Great Black-backed Gull, Hooded Crow (Corvus cornix), Ruddy Turnstone (Arenaria interpres), terns (Sterna spp.), Peregrine Falcon (Falco peregrinus), and Northern Goshawk (Accipiter gentilis; 83, 108, 99, 19). Predation by feral American mink (Mustela vison) widespread in n. Baltic and w. Scotland (109, 19).

Ruddy Turnstones rob nests of eggs (108). Predated eggs typically show evidence of being pierced by bird bills (100).

Adults

Some loss from hunting (100). Killed in n. Baltic and w. Scotland by feral American mink (109, 19).

Response To Predators

During chick-rearing stage, response to human intrusion is combination of circling above (passive mobbing) or swooping down on intruder (active mobbing). Most attacks on intruders exclude actual physical contact, but some pairs strike intruders with their feet. As breeding season advances, both frequency of attacks (attacks/min) and attack rate (attack frequency/number of potential mobbers) increase. Of 19 pairs with chicks, 26% were attackers; of 2 colonies, the one with the higher attack rate had greater reproductive success (7).

Communal defense used, but not universally. Rate of predation on eggs in colonies significantly lower than on eggs in solitary nests (110). Distraction displays rare in Finland, and in all cases performed only after eggs have hatched (100, 7). In Ireland, adult male performed display after leaving islet breeding territory and flew in front of a nearby boat, half alighting on water and beating its wings, then flying a short distance and repeating wing beating; this done repeatedly (111). Solitary pairs will move their young up to 2 km from breeding place when presence of predators detected (99).

Phenology

Pair Formation

Some pairs arrive together on breeding grounds; in other cases, one mate settles before the other arrives (99). In Finland, date of breakup of ice affects timing of arrival at breeding site (60). Elsewhere, factors governing timing of arrival little known. See Migration, above, for dates of return to nesting areas.

Nest-Building

No information.

First/Only Brood Per Season

In Ireland, egg-laying begins 15–20 Apr, 2 wk earlier than in Scandinavia and former USSR (2).

Departure of Young from Nest or Cessation of Close Parental Care

Young begin to leave nest 1–2 d after hatching (92).

Second/Later Brood Per Season

In Russia, begin new nests 5–7 d after experimental removal of primary clutches. 90% of replacement eggs require minimum of 48 h to be laid; only 52.4% of primary nest eggs require this amount of time (112).

Nest Site

Selection Process

Both a tree - and ground-nester. Nest-site choice reflects limitations imposed by habitat and threats of predation. Strong nest-site tenacity; see Demography and populations: range, below. Former mates that arrive simultaneously recognize their former nest site and often build their nest in same spot. Abandons nest site when eggs/chicks stolen or killed (99). See Nest, below.

Microhabitat; Site Characteristics

Coastal and inland nest sites differ. In Europe (including Russia), uses bare soil or rocks, stony areas, pine (Pinus sp.) branches and nests of other birds at a height of 6–7 m (113, 114). In sw. Finland, nest sites have 3 features: a solid foundation, typically a niche, crevice, or platform ensuring that nest would not disintegrate; sites overlooking a considerable portion of the sea because nonincubating mate spends considerable time guarding nest on an overlook within vicinity of nest; and sufficient distance from trees to guard against predation by Hooded Crow. Smallest distances are 7 m from pine trees 3-m tall and 13–14 m from pines about 6-m tall (5). Idiosyncratically nests on roofs in Aberdeen, Scotland, and Tallinn, Estonia (106, 115).

Nest

Construction

Method of construction, time of day spent, and length of time required to build nest undescribed.

Structure And Composition Matter

Nest materials differ by location. Shallow cup of vegetation, mainly dry grass, frequently with a stone centrally placed (2). In nw. Russia, instead of rarely used twigs, uses grass stems, moss, and seaweed yielded by surf activity (114). In n. Norway, heaths depauperate of nesting material lead to nests with little material (102).

Dimensions

No information.

Microclimate

No information.

Maintenance Or Reuse Of Nests, Alternate Nests

Reuse of old nests common. In 1985, in archipelago southwest of Helsinki, one nest site used for 23 consecutive years. From 1979 to 1985, in same archipelago, about 50% of nests (113 of 224) in colonies were located in precisely same places as previous season, even though all eggs and young had been lost at a stage that would have caused solitary pairs to desert nest site (99).

Eggs

Shape

No information.

Size

Kandalaksha Bay, White Sea, Russia: 58.5 × 41.7 mm (n = 425). Norway: 57.2 mm ± 2.5 SD × 41.0 mm ± 1.4 SD (100).

Color

Eggshell patterns correlate with laying sequence; proportion of elongated spots on a shell increases with laying sequence. When elongated spots are common on all eggs, spots on third egg are smaller than on first 2 (116).

Surface Texture

Smooth and somewhat glossy.

Eggshell Thickness

From 117, unit of measurement 0.02 mm. From 1869 to 1952: 9.6 ± 0.25 SE (n = 18). From 1977 to 1978: 9.33 ± 0.32 SE (n = 15).

Clutch Size

In Norway, 82% of 122 clutches had 3 eggs (118). Supernormal clutches (4 or 5 eggs) rare or lacking: in Norway, none supernormal among 122 clutches (118).

Egg-Laying

Evenly distributed throughout day; most eggs laid during day, but differences between time periods among European birds not significant: 20:00–04:00, 30.5%; 04:00–12:00, 33.6%; 12:00–20:00, 35.9%. Average interval between laying of first and second eggs and second and third eggs is same, 45.4 h. Average time required to complete laying of 3-egg clutch = 89 h (118).

Parental Behavior During This Period, Including Sexual Guarding. Young protected by parents from neighbors as well as other conspecifics (92).

Replacement of Individual Eggs or Clutches. In Europe, some pairs replaced lost clutches twice; mean of 7 replacement clutches = 1.7 (34).

Incubation

Onset Of Incubation

In Europe, incubation usually begins after last or earlier egg is laid (119). In Ireland, in most cases incubation starts with second egg, some even after first egg (2).

Incubation Period

In Europe, incubation period is 25.9 d ± 2.0 SD (n = 56; 113).

Parental Behavior

No information.

Hatching

Can be either synchronous or asynchronous, with maximum of 2 d between hatching of first and third chicks (2).

Young Birds

Leave nest within 3–5 d but remain near nest (34). Start flying at about 4 wk, fly well at 5 wk (119). In Estonia, growth pattern under experimental conditions as a function of time resembled sigmoid curve. Young birds weighed 36 g on first day, reached maximum of 386 at 32 d, and 380 on 36th d. Growth rate most rapid during second 4-d period (3). In Ireland, growth started to level off about 22 d of age when chicks 300–350 g (2). Heaviest chicks in Russia reached maximum mean body mass of 460 g at 20–30 d, then dropped to average of 430 g before fledging at 25–30 d (114).

Parental Care

Brooding

Parents cover bodies of young only during first few days after hatching, after that only during inclement weather. At breeding territory, guard young from adults and other young (92). Perform distraction displays to lead potential intruders away from nest site (111).

Feeding

Just after hatching, parents feed chicks a semidigested mass, transmitting it bill to bill (92). While both parents feed young, female is primary provider (34). No information on feeding rates. In former USSR, fed mainly on insects, small fish, and crustaceans (Gammaridae) up to 4 d; from 4 to 17 d, ate primarily insects and small fish, on occasion berries; at 3 wk, young may find own food (34).

Nest Sanitation

No information. Likely not an issue because precocial chicks leave nest after a few days.

Parental Care Of Young

Parents recognize young after about 5 d, apparently using dark marking on chick's crown as cue (34). Nonetheless, adoption common. On islands of Vistula River (Poland), in 1997, 81 chicks from 35 nests were adopted (40% of all pairs), almost always by neighbors. The shorter the internest distance for males, the greater the genetic similarity of adopting parents, suggesting indirect fitness benefits for adopting neighbors (120).

Brood Parasitism by Other Species

Instances of egg-dumping in several nests in Scotland well after start of incubation had begun (121). In Germany, Mediterranean Gull placed an egg in Common Gull's nest; young Mediterranean Gull was fed and discriminated between its adoptive parents and other Common Gulls (122). In Scotland, a Parasitic Jaeger deposited 1 egg in a Common Gull nest with 2 eggs and then incubated its own egg and the Common Gull eggs (123).

Fledgling Stage

Departure From Nest

Chicks do not leave breeding territory immediately after developing capacity for flight (92).

Growth

No information.

Immature Stage

Little information from period of independence until breeding. In Ireland, second-summer birds occasionally chased out of breeding colonies (2). During winter, tend to linger at feeding places longer than adults (95). Immatures generally remain together during fall migration (34).

Measures of Breeding Activity

Age At First Breeding; Intervals Between Breeding

Males reach sexual maturity earlier than females: males mature at 2-3 yr, females at 3-4 yr (34). In Estonia, 59.4% of males began to breed at age of 3 yr, 32% at 4 yr (n = 175); 42.9% of females began to breed at 3 yr, 50% at 4 yr (n = 56; 6).

Clutch

See Breeding: eggs, above.

Annual And Lifetime Reproductive Success

In w. Scotland, in colonies without nest predation, 0.34-0.42 fledglings/pair in 1992 (n = 9 colonies, 591 pairs) and 0.19-0.45/pair in 1993 (n = 12 colonies, 486 pairs; J. C. A. 19). In Ireland, over 7-yr study period, 20-52.5% of completed clutches failed to produce live young; reproductive success (fledged juveniles/eggs) averaged 22.9% (range 11-38.4; 2). In Finnish colonies, production of 0.2 and 1.8 fledged young/pair (n = 210 and 215 pairs, respectively; 34).

Loss of eggs and chicks influenced by several factors, including predation (see Behavior: predation, above), gnat infestations causing fatalities from parasitism, brood desertion, death of embryos, insufficient care of young (124), and heavy winds (125). No data on loss of young.

Number Of Broods Per Season

Normally rears only 1 brood.

Life Span and Survivorship

Recorded longevity of 33+ years 126.

In 25-yr study in Estonia (6), only 9% of given cohort survived until breeding age. 45% of hatched chicks survived until fledging; 59% of these died before next breeding season. Mortality in second year 29%; in third year 19%. Mortality of breeding birds averaged 13%/yr.

In Scotland, maximum age at death of banded birds 12 yr (males) and 8 yr (females; 19).

Disease and Body Parasites

Commonly infected by a wide variety of helminth species that are gull generalists (127). Seasonal pattern to rates of infection: number of species lowest in Apr, at maximum in Jun/Jul (128). In Norway, 11 different cestode species from 3 orders found in 86% of 269 gulls, with 17.1 individuals and 1.6 species/infected gull. Most commonly observed species was Anomataenia micracantha, present in 50% of gulls (129). In same group, 16 species of Digenea from 9 families found, the 2 most common of which were Cryptocotyle lingua and Plagiorchis laricola; also 12 species of nematodes (130, 131). See also 132 and 124 .

Young infected by age of 3 d with helminth species Leucochloridium macrostomum (133). Helminth communities develop quickly in unfledged birds and diversity patterns become similar to immatures and adults (128). Adults infected with average of 2 species of Digenea, immatures and juveniles with 1 species. Males more subject to infection than females (133), but no sex differences in diversity parameters (128). In Europe, young affected by mass blackfly (Simulium) outbreaks.

Degeneration of liver and other internal organs found in birds with concentrations of PCBs (polychlorinated biphenyls) in Gulf of Finland; causality between PCB residues and chick diseases unclear (134).

Causes of Mortality

Known causes of mortality include predators (see Behavior: predation, above).

Population Status

Numbers

No precise data. Global population may exceed 1 million pairs, according to Burger and Gochfeld (57), although a global estimate of 578,000-585,000 pairs was given by Lloyd et al. (135), which may be low given an estimate of 416,157-558,316 for Europe alone (136). More recent reports suggest much higher estimates for populations with the global population estimated at 2·1–3·3 million individuals; of these race canus is the most abundant, with up to 2·25 million birds, followed by heinei with up to one million birds; and camtschatschensis is the scarcest race, with up to 100,000 individuals (137).

The European breeding population, including all race canus and some heinei in European Russia estimated at 1,280,000–2,160,000 mature individuals and is largely regarded as stable; the largest European breeding populations are in European Russia (250,000–600,000 pairs), Sweden (71,000–132,000 pairs), Finland (70,000–90,000), the UK (49,000 pairs) and Germany (22,000–24,000 pairs). Large-scale population displacements occur in winter. For example, during surveys in 2003–2004 to 2005–2006, the total overwintering population in the UK was estimated at 705,392 individuals (138).

Trends

In w. Palearctic, substantial increases in most of range, especially in twentieth century (34). Race canus increased and spread in Europe during 20th century, colonizing many new areas, including Iceland; it has bred in Poland and Austria mainly since 1950s. Counts in the Wadden Sea, Netherlands, between 1980 and 1991 showed increases over counts taken from 1965 to 1977 (139). Reasons for increase unknown.

Population Regulation

No data. Likely that principal influences on population numbers are adequate food resources and nesting habitat; secondarily, harsh weather and human disturbance. Where threatened by predators, especially exotic species, reproductive success suffers. However, long-term impact of any single factor on populations is unclear.

Not globally threatened (Least Concern). The global population has been estimated at 2·1–3·4 million individuals; of these race canus is the most abundant, with up to 2·25 million birds, followed by heinei with up to one million birds; and kamtschatschensis is the scarcest race, with up to 100,000 individuals (137).

Effects of Human Activity

Shooting And Trapping

Species has suffered some direct persecution from egg collecting in Germany, Scotland, the Russian Federation and Poland, and shooting in the Russian Federation 140.

Pesticides And Other Contaminants

Absorption of extremely high levels of fluoride by females in Norway near aluminum smelters from 1991 to 1993 led to a higher concentration of bone fluorine than males had (141). Eggs from nw. Russia contained DDE and lindane in 1989 and 1990, although concentrations were not at levels likely to affect reproductive success (142). In Hungary, in 1995, deltamethrin, active ingredient in an insecticide used against mosquitoes, was found in tissues of dead birds (143).

Ingestion Of Plastics, Lead, Etc

No information.

Collisions With Stationary/Moving Structures Or Objects

Of 70 species involved in aircraft strikes in United Kingdom, third most prevalent; often congregates on airfields to feed on soil invertebrates (144). In United Kingdom, 1 of 3 gull species at Edinburgh Airport posing a hazard to aircraft; 2 collisions in 1960s caused by winter feeding and roosting patterns, as birds fly over airport at dawn and return at dusk (145).

Fishing Nets

No information.

Degradation Of Habitat

Breeding habitat loss has resulted from land reclamation, drainage, and afforestation. Habitat losses also affect winter quarters (140). European populations have also been variously threatened by predation from introduced ground predators such as American mink (Neovison vison).

Disturbance At Nest And Roost Sites

European breeding colonies face disturbance by anglers and other human visitors.

Human Impacts

Where fed on regular basis, becomes tame and flight distance from people no more than 1-3 m. For others, flight distance typically 10-20 m. If threatened on breeding territory with a stick or by thrown stones, will retaliate with aerial attacks. Even 1 wk later, people resembling attackers (e.g., dressed like them) will be threatened by gulls if they approach the territory. Also apparently learns to recognize regularly encountered boats (99).

Management

Conservation Status

Not globally threatened (Least Concern). Not threatened in any part of its range. Global population possibly >1 million pairs.

Priorities for Future Research

Although Common Gull has now been split from Short-billed Gull, questions remain, especially on the taxonomic status of "Kamchatka Gull". More comprehensive genetic studies comparing samples across Eurasia and between North America and European birds are needed.

Acknowledgments

We thank the following people for their assistance: Christine Bush, Christopher L. Caprette, Doug Causey, Susan Cloud, Robert H. Day, Donna L. Dittmann, Jon L. Dunn, Paul Lehman, Sandra L. L. Gaunt, Clayton Gray, Jr., Luana Heikes, Joann Jacoby, Simon Perkins, Wayne Petersen, Alison Pierie, Alan Poole, Keith Russell, Sandra Sherman, Rand Smith, and Angus Wilson. Unpublished information on Yukon distribution was provided by Pam Sinclair, Canadian Wildlife Service, Whitehorse.

About the Author(s)

William Moskoff is Hollender Professor of Economics and Biology at Lake Forest College, where he teaches field ornithology. He received a B.A. in economics from Hunter College and an M.A. and Ph.D. in economics from the University of Wisconsin and an M.S. in biological sciences from the University of Illinois-Chicago. He has authored or co-authored 4 previous BNA accounts: Veery, Solitary Sandpiper, Philadelphia Vireo, and Lesser Yellowlegs. Currently at work on a book about bird aggression, he has written on aggressive behavior of Ring-billed Gulls and the two yellowlegs species in feeding associations. Current address: Department of Biology, Lake Forest College, Lake Forest, IL 60045-2399. E-mail: moskoff@lfc.edu.

Louis R. Bevier is an assistant editor of The Birds of North America project. He is also a part-time guide leading bird-watching tours for Field Guides, Inc. He received a B.A. in environmental biology from the University of California Santa Barbara and has participated in a number of studies on birds with faculty there. He edited The Atlas of Breeding Birds of Connecticut and contributed species accounts or editorial advice to several field guides on North American birds. He is currently working on an avifaunal treatment for the birds of Maine with 2 co-authors. Current address: 46 Back Rd., Fairfield, ME 04937-3127. E-mail: lrbevier@colby.edu.

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  • Migration
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  • Non-Breeding

Recommended Citation

Moskoff, W., L. R. Bevier, and P. C. Rasmussen (2021). Common Gull (Larus canus), version 1.1. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.mewgul.01.1