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Great Black-backed Gull
Larus marinus
Order
CHARADRIIFORMES
– Family
LARIDAE
Authors: Good, Thomas P.

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Behavior

Locomotion

Walking, Hopping, Climbing, Etc

On land, typically walks or runs with legs alternating, a more lumbering gait than that of smaller gulls. Can jump or hop onto perches by opening wings, using single beat of wings for elevation, and pushing off with legs. Hops down from perches with wings partly spread. In agonistic charges, runs with wings partly raised. Runs to take off for flight. Does not use hopping as form of locomotion. Does not climb vertical objects.

Flight

To regulate speed, adjusts wing-beat and orientation to wind. Spends considerable portion of flight time gliding or soaring with outstretched wings. Dives and swoops by adjusting angle of wings. Often descends by flapping wings and flying in diminishing circles when joining feeding groups on water. Attacks terrestrial predators using steep dives; strikes at predator with wings, feet, and (rarely) beak.

Swimming And Diving

Swims on surface of water using paddling motion of legs for propulsion. Can dive either from surface or from short distance above water, but does not typically reach depths >1–2 m below surface (Ingolfsson 1969b, Seymour 1974, TPG).

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing, Anting, Etc

Not known to ant. Bathes regularly while resting on water, dunking head and body parts underwater and shaking them. Combines bathing and preening on water. On land, preens using beak on wing-, breast-, and tail-feathers. Rubs head over preen gland, and then rubs secretion on feathers. Fatty acids of preen gland are different from those of Herring Gull, Common Murre, Black Duck (Anas rubripes), and Northern Fulmar (Fulmarus glacialis); general chemical composition is similar to that of phytoplankton, copepods, herring, and cod; composition variable and linked to diet (Levy and Strain 1982). Scratches head while preening, by extending leg under wing.

Sleeping, Roosting, Sunbathing

Sleeps with head resting on breast and legs folded underneath body; some individuals sleep while perching on 1 leg, with other leg folded against body. Deeply sleeping bird tucks head under wing along back. Sleeps while incubating or next to incubating mate.

Roosts and loafs in large groups (often mixed species) in open areas that allow large distance between group and approaching predators, including fields, beaches, parking lots, helipads, airport runways, and garbage dumps. Winter aggregations in Maine average <500 but can reach 5,000 (Wells 1994).

Daily Time Budget

Before egg-laying, foraging patterns strongly correlated with tidal cycles; almost no birds on colony during low tides (Verbeek 1979). Adult makes few trips during breeding: mean 2.9 trips/d (range 1.3–4.7, n = 3 birds); duration of foraging trips less than that of Herring Gull, showing no increase through breeding: mean 1.7 h (range 1.0–2.2, n = 3 birds); P. M. Cavanagh unpubl. data). Before chicks hatch, female spends more time than male on territory (t = 51.1, n = 19, p < 0.05) and brooding (t = 32.0, n = 19, p < 0.005); after chicks hatch, time on territory and brooding time are not significantly different for male and female (Butler and Janes-Butler 1983). Before chicks hatch, male and female are on territory in early morning, late afternoon, and evening, and territory is left unattended for not >1–2 min; after chicks hatch, male and female are on territory in late afternoon and evening (Butler and Janes-Butler 1983). First 20 d after chicks hatch, one or both adults are in attendance (Butler and Janes-Butler 1982). Subsequently, periods of territory attendance are similar between sexes but markedly reduced; some chicks are left unattended for up to 8 h (Butler and Janes-Butler 1983). During breeding, longer foraging trips by male and female (mean 2.0 h ± 0.5 SD, n = 140) than for Herring Gull male (mean 1.2 ± 0.4 SD, n = 176) and female (mean 1.1 ± 0.4 SD, n = 184); chicks are fed less often (1.4–1.8 feedings/d, n = 5 nests) than are Herring Gull chicks (2.2–3.5 feedings/d; Pierotti 1979).

Adults spend most time on territory sleeping or resting. Spend most of the day in colony site during breeding: mean 18.9 h/d (range 14.3–21.4, n = 3 birds; P. M. Cavanagh unpubl. data). In nonbreeding season, forage 2–3 h/d; rest, sleep, and preen remainder of time.

Agonistic Behavior

Physical Interactions

Chases inter-and intraspecific intruders, both in air and on ground, and may attack them. Neighbors begin attacking each other by jabbing at opponent with beak, and grabbing opponent by tail, wing, beak, and rarely by neck. Birds gripping each other by beak engage in extended pulling bouts (Tinbergen 1960), strike with wings, or peck. Attack on intruders usually begins with Charge (see below). Bird retreating from opponent often gives Shrill Waver or Alarm Call (see Sounds: vocalizations, above). Bird also pursues retreating opponents by flight, or on ground with wings raised. Male engages in fights and pursuits much more often than female does; attacks and fights, although rare, can result in eye and wing injuries (Butler and Janes-Butler 1983). Low-density colonies may show little or no intraspecific agonistic interactions (Pierotti 1979). After chicks hatch on breeding colonies, mean aggression rate increases 25-fold toward Herring Gulls and 50-fold toward conspecifics; distance that birds will chase both Herring Gulls and conspecifics is greater after chicks hatch (Burger 1983). Frequency of agonistic interactions doubles in morning and early evening; frequency of agonistic interactions is halved in late afternoon, when ambient temperatures are higher and adults and chicks are asleep or inactive (Butler and Janes-Butler 1983).

Adult may attack chicks running across territory. Typically grabs chick by head and shakes it. May grab smaller chick by body, and pummel it, throw it, or swallow it whole. Only a few males (sometimes none) in any single colony engage in such infanticidal attacks. Adult also attacks first few chicks to fledge in area. Attacks on fledglings involve repeated swoops, and blows struck with wings, feet, and bill—sometimes involving several adults. Male threatens and attacks female infrequently when female attempts to eat food regurgitated by male for chicks (Butler and Janes-Butler 1983).

Communicative Interactions

Complex repertoire; many distinct displays. Several displays linked closely with vocalizations, after which they are named (see Sounds: vocalizations, above). Many displays have multiple context-dependent functions (Beer 1975). Therefore, displays not subdivided into threat and appeasement, although these functions are discussed.

Upright Posture. Aggressive Upright of Cramp and Simmons 1983 . Most common threat display. Approaches opponent slowly in rigid posture with neck stretched upward and forward and head pointed slightly downward. In high-intensity forms, lifts wings so they stand out from body, positioned to strike blows. Given significantly more often by male than by female, increasing significantly in both sexes after chicks hatch; directed at neighbors proportionally more than nonneighbors (Butler and Janes-Butler 1983). Often leads to Grass-Pulling (see below) or exchange of Long Calls with neighbors. With intruder, if opponent does not retreat, displaying bird begins to approach more rapidly, raises wings more prominently, grading into Charge.

Charge. Also called Attack or Supplant. Bird approaches opponent rapidly, half running, half flying, often giving Charge Call (see Sounds: vocalizations, above). Intruder almost invariably flies in response. Pursues persistent intruders through air and, if necessary, attacks them. Male more likely to Charge, especially after chicks hatch. Female intruder elicits Charge by both sexes; directed at nonneighbor proportionally more than neighbor (Butler and Janes-Butler 1983).

Alert Posture. Anxiety Upright of Cramp and Simmons 1983 . Same as Upright Posture (see above), except holds neck back and bill at or slightly above horizontal. Often given by target of Upright Posture. Also given in presence of predator before flight.

Oblique Posture. From Cramp and Simmons 1983 . Associated with Long Call (see Sounds: vocalizations above). Bird lowers head toward ground (not as far as does Herring Gull) and produces Long-Call Notes. Throws head back (not as far as does Herring Gull), stretches neck out fully with mouth wide open (body forms oblique angle with substrate; hence the name of this display) while emitting Long Call. Given after bout of aggression over territorial boundary, when mate returns from absence, when neighbor returns from absence, and at bird flying over territory. Oblique Posture without Long Call functions as threat when given by bird stretching neck toward opponent across boundary.

Silent Squat. Also called Squat-and-Freeze or Face-off (Butler and Janes-Butler 1983). Bird crouches with breast touching or just above substrate, rear end elevated. Head in position similar to that of Upright Posture (see above). Often alternates with bill jabs or Grass-Pulling (see below). Directed only at neighbors while face to face. Given by males more often than by females; given by females especially after chicks hatch (Butler and Janes-Butler 1983).

Grass-pulling. During territorial disputes, one or both opponents take vegetation in beak, brace feet wide apart, and pull vigorously at vegetation (Tinbergen 1960). Low-level agonistic act usually performed while facing neighbor opponent <1 m away. Less commonly observed than in Herring Gull; ritualized version may be performed by failed breeders in absence of territorial dispute (Cramp and Simmons 1983). Similar posture taken by bird grasping opponent by wing, tail, or beak during fight (Tinbergen 1960); may be displacement activity. Given by male much more than by female; given by female more after chicks hatch (Butler and Janes-Butler 1983).

Choking. Display accompanying Choking Call (see Sounds: vocalizations, above). Lowers breast, bends legs, points head down, and depresses hyoid bone, making throat look swollen. Performs rhythmic jerking movement with head, producing deep call. Typically given by pair in tandem during territorial boundary disputes (Cramp and Simmons 1983). Same display is directed at partner when identifying nest scrapes and during nest exchanges; in these cases, given by bird on nest or over scrape.

Mew Call Posture. Similar to Upright Posture (see above), except neck more arched and head lowered with mouth open so that Mew Call can be produced. Attracts mate or chick when given after returning to territory; often precedes regurgitation of food for mate or offspring. Also given in nest relief and territorial disputes, when intruder lands on territory. In latter cases, appears to function as high-intensity threat.

Head-Tossing. Associated with Begging Call (see Sounds: vocalizations, above). Hunches neck so that head is drawn close to body. Repeatedly flicks head upward, giving Begging Call with each toss. Appears to stimulate regurgitation by male when given by female, or by either parent when given by chick or juvenile. Given by both members of pair during initial phases of courtship-feeding sequences and in tandem before copulation (see Sexual behavior, below; Cramp and Simmons 1983). Frequency of Head-Tossing in male and female is similar before chicks hatch. After chicks hatch, given more by female than by male, and given by male less than before chicks hatch (Butler and Janes-Butler 1983).

Facing-Away. Similar to Upright or Alert postures (see above), with neck stretched vertically to maximum and head and body horizontal. Individual, or at least head, is turned away from other bird, which means weaponry (wings, beak) is also turned away. May function in appeasement, allaying opponent’s fear, or in cutting off visual stimuli from other bird that might provoke its own flight or attack behavior (Beer 1975). Given during boundary disputes, by mates upon return of partner, and by chicks (directed at parents) after parents display at other adults.

Spacing

Territoriality

Maintains breeding territory on colony during breeding season. Territory established by male; defended by pair. In winter, defends feeding or nesting sites (see Winter territoriality, below).

Nature and Extent of Territory. Breeding territories are areas of substrate defended against conspecifics or congeners. Least colonial of larids. In Sweden, breeds solitarily or in small colonies of about 7 pairs; least likely of larids to be found in mixed-species colonies (Gotmark 1982). Along northern shore of Gulf of St. Lawrence and s. Labrador, generally seen nesting solitarily (Gross 1937). Territory size depends on nature of substrate and heterogeneity of terrain. On Little Duck I., ME, distance to nearest neighbor averaged 6.7 m ± 0.8 SE (n = 51; Butler and Janes-Butler 1982); distance to nearest neighbor averaged 4.7 m ± 0.5 SE (n = 15) on high-density territories and 12.1 m ± 1.2 SE (n = 9) on low-density territories (Butler and Trivelpiece 1981). On Appledore I., ME, mean distance to nearest neighbor ranged from 4.9–5.6 m ± 0.23 SE (n = 117; McGill-Harelstad 1985, TPG) to 6.7 m ± 3.9 SD (n = 99; Burger and Gochfeld 1983). In New Jersey, individuals nesting among Herring Gulls were spaced solitarily with respect to conspecifics (Burger 1978). On Walney I., England, nearest-neighbor distance of nonsolitary nesters averaged 21.6 m ± 10.3 SD (range 6.1–49.68, n = 37; Verbeek 1979).

Size of defended area changes during breeding season, especially if chicks hatch early or territory has few contiguous neighbors (Butler and Janes-Butler 1982). Changes relate to value of territory and settling pattern. During earliest stage, fewer pairs are settled and defended areas are larger. After chicks hatch, parents are much more aggressive; attack all intruders in area and strongly defend boundaries against neighbors (Butler and Janes-Butler 1982, 1983). Estimated territory size averaged 35.4 m2± 6.8 (n = 15) for high-density pairs and 149.9 ± 24.3 m2(n = 9) for low-density birds. Territorial boundaries are quite flexible, depending on context; small “unique territory” is defended against all birds other than pair and offspring, and “primary territory” is defended only against neighbors. Territoriality not observed on Great I., Newfoundland; pairs maintained large, overlapping areas encompassing 5–6 breeding territories (Pierotti 1979). Rare (<2% of post-hatch agonistic interactions) defense beyond primary territory (e.g., in adjacent territory) always directed at nonneighbors, always after chicks hatch, and usually while neighbors are absent (Butler and Janes-Butler 1982).

Manner of Establishing and Maintaining Territory. Arrives at colony already paired or forms pairs at colony (Cramp and Simmons 1983). Male performs most defense and maintenance of territory (Butler and Janes-Butler 1983). Established pair typically returns to same territory as long as they remain paired.

Interspecific Territoriality. Nests in mixed-species colonies with other gulls, terns, skimmers, alcids, and eiders; rarely with cormorants and gannets. Defends territories only against other gulls: Glaucous, Herring, Ring-billed (Larus delawarensis), and Laughing gulls along Atlantic Coast and Great Lakes. Often supplants smaller species; usurps breeding habitat by arriving before other larids. Will attack and kill smaller species.

Winter Territoriality. Defends feeding or resting sites against conspecifics and congenerics using Upright Posture and Long Call (see Agonistic behavior, and Sounds: vocalizations, above); strangers at roost and feeding sites engage in elaborate meeting ceremony, involving lengthy exchange of postures and vocalizations (Cramp and Simmons 1983). Some individuals or pairs defend feeding territories throughout year (R. Pierotti pers. comm.).

Dominance Hierarchies. Dominance is context-specific. Adults typically are dominant over juveniles or immatures. Male may dominate female during feeding and boundary disputes; female may win conflicts over choice of nest site and incubation. Dominant to all other gull species on and off colonies. Most frequent scavenger at salmon (Salmo salar) carcasses in Scotland; dominant to crow (Corvus corone) at carcasses but subordinate to Grey Heron (Ardea cinerea; Hewson 1995). Kleptoparasitizes from and is kleptoparasitized by Bald Eagle (Lien 1975, Sobkowiak and Titman 1989); in >90% of interactions, loses prey or carrion to Bald Eagles (Sobkowiak and Titman 1989).

Individual Distance

Maintains personal space on roosting areas in both breeding and nonbreeding seasons. May roost in dense groups at landfills, on ice floes, and on beaches (TPG).

Sexual Behavior

Mating System And Sex Ratio

Almost exclusively monogamous. Unusual behavior reported: male and female from separate established nests on Great I., Newfoundland, established third nest together. Two days of nest-building were followed by Choking (see Agonistic behavior: communicative interactions, above) but not by copulation (Pierotti 1979). Rate of mate replacement following dissolution of pair or death unknown. At least 2 parents are necessary to successfully rear offspring; eggs left alone in nests are often eaten, and offspring left alone may be attacked or killed. Sex ratio in North America unknown. Sex ratio in Russia reported as 1.5 males:1 female (Cramp and Simmons 1983).

Pair Bond

Courtship Displays and Mate-Guarding. Territorial male attracts potential mate by assuming Oblique Posture (see Agonistic behavior: communicative interactions, above) and giving Mew Call (see Sounds: vocalizations, above). May also perform Advertisement Flight, flying often with slower-than-normal wing-beats, head and neck outstretched, periodically giving variant of Long-Call Note; given to female on territory, who may join and follow some distance behind (Cramp and Simmons 1983). Female lands on territory some distance from male, giving Facing-Away display on landing (see Agonistic behavior: communicative interactions, above); male may give same display. If tolerated, female typically approaches male in hunched posture, giving Head-Tossing display and Begging Call (see Agonistic behavior: communicative interactions, and Sounds: vocalizations, above). Male responds either (1) by assuming either Upright Posture or (2) by assuming Mew Call Posture and giving Mew Calls. Female circles male, increasing begging intensity if he gives Mew Calls. Male may either give Choking display (above) or regurgitate and feed female. If male regurgitates food and female accepts it by eating; often leads directly to copulation.

Copulation; Pre- and Postcopulatory Displays. Male and female give Head-Tossing display (see Agonistic behavior: communicative interactions, above) together repeatedly, female typically more than male. Male moves behind female, mounts her with wings outspread, and wags tail rhythmically from side to side. Female continues Head-Tossing and may pull at male’s breast-feathers while male continues tail-wagging and Copulation Call (see Sounds: vocalizations, above). Tail-wagging and accompanying Copulation Call speed up until cloacal contact is made; 1–7 (mean 3) cloacal contacts made (Cramp and Simmons 1983). After copulation, male jumps off of female, shakes, and preens. Either male or female may terminate copulation. If female does not eat food regurgitated by male, she may prevent him from mounting by walking away (TPG).

Duration and Maintenance of Pair Bond. Pair bond is maintained over multiple seasons (Cramp and Simmons 1983), possibly for life. No data on percentage of pairs that break pair bond. Rupture of pair bond possible after eggs fail to hatch because male provides inadequate food to female during egg formation or because male and female do not synchronize activities, leaving eggs unattended and allowing them to be eaten; incipient and failed breeders may increase egg predation (Butler and Trivelpiece 1981, TPG). Extra-pair activity observed on Great I., Newfoundland, after eggs failed to hatch (Pierotti 1979). Single parent abandons nest if mate is removed late in incubation; time to abandonment is equal for males (mean 2.6 d ± 1.5 SD; range 1–7 d, n = 17) and females (mean 3.0 d ± 1.2 SD; range 1–4 d, n = 5); Transue and Burger 1989).

Extra-Pair Copulations

Paired, territory-holding male may solicit copulation from other (usually neighboring) territory-holding females. On Great I., Newfoundland, male and female from separate nests established third nest, collecting material and building nest cup. Pair performed Choking display (see Agonistic behavior: communicative interactions, above); copulation not observed and eggs not laid (Pierotti 1979).

Social And Interspecific Behavior

Degree Of Sociality

Nests in loose colonies (see Spacing, above); social interactions between neighbors range from agonistic in dense breeding situations to tolerant in sparse situations. Appear to nest as far apart as limited space allows. If sufficient habitat available, nests solitarily or in small colonies (Gotmark 1982). Away from breeding colony, birds loaf and roost in groups; forage in aggregations when prey is located. Foraging groups often include other Larus species, as well as kittiwakes, cormorants, shearwaters, alcids, dolphins, and whales (Pierotti 1988). Behind fishing vessels, groups often include skuas, Northern Fulmars, Northern Gannets [Sula bassana], and other Larus species (Furness et al. 1992).

Play

Chicks and juveniles play. Often pick up objects and run around territory. Other chicks may pursue during these activities, attempt to steal object. Tugs-of-war lasting >1 min may ensue. Practice flight contains elements of play; chicks within brood leap up and down beating wings and chittering (TPG).

Nonpredatory Interspecific Interactions

Forages, loafs, and roosts in mixed-species groups (see above). Interspecific interactions with crows and other gulls. Eider ducks nest in higher densities and experience lower nest depredation within Great Black-backed Gull colonies than in other gull colonies or on gull-free islands (Gotmark and Ahlund 1988); number of eider nests increasing as Great Black-backed Gull numbers increase on Appledore I., ME (Borror and Holmes 1990). Interspecific territoriality with other gull species (see Spacing, above). Usurps breeding habitat by arriving before other larids and terns.

Predation

Kinds Of Predators

Few predators on adults: Bald Eagles, domestic dog (Canis familiaris). On chicks: conspecific adults, other sympatric gulls (rare), Bald Eagles, Common Raven (Corvus corax), domestic dog, domestic cat (Felis catus). On eggs: conspecifics, other sympatric gulls, ravens, crows (Corvus spp.), raccoons (Procyon lotor), Norway rats (Rattus norvegicus; Tinbergen 1960, TPG). Humans still remove eggs from the few Great Black-backed Gull nests and many Herring Gull nests on Kent I., New Brunswick (J. C. Johnston pers. comm.).

Manner Of Predation

If adult injured and unable to fly, can be killed by dog. Conspecific adults, other sympatric gulls (rare), Bald Eagle, Common Raven, domestic dog, and domestic cat prey on chicks in colonies. Conspecifics, other sympatric gulls, ravens, crows, raccoon, and rats (Tinbergen 1960, TPG) prey on eggs in nests.

Response To Predators

When predator is first sighted, individual gives Alarm Call (Cramp and Simmons 1983). If predator approaches, gives Warning Call, takes off, and circles overhead. Mobs flying predators (eagles, hawks, ravens) by pursuing through air. Circling individuals are silent or utter deep Warning Calls (see Sounds: vocalizations, above, for descriptions of Alarm and Warning calls).

Attacks human intruders silently at ≥45° angle, then issues rapid Alarm Calls, with legs extended; does not ignore intruder, gather on sea surface, or give distraction display (flying low over water and dangling feet) as does Herring Gull (Kilpi 1988). Generally more wary of humans than other gulls are; response intensity is a function of prior disturbance level and incubation stage. Individuals become alert, call, stand, walk, and fly more rapidly than do Herring Gulls; take longer to resettle than do Herring Gulls (Burger and Gochfeld 1983). Attack rate on colony increases over breeding period (0.1 attacks/min during incubation; 1–1.1 attacks/min during chick-rearing); 94% of pairs circled >100 m away and 70% of pairs remained silent during incubation, while 14% of pairs circled >100 m away and 14% of pairs remained silent after chicks hatched (Kilpi 1988).

Dives at terrestrial predators; strikes with feet, wings, and rarely beak. Defends air “territory” against strange gulls attracted to disturbances, preventing communal defense (Kilpi 1988). In response to stuffed mink on territory, solitary pairs actively attacked other gulls, preventing them from mobbing model; pairs divided labor of attacking model and patrolling for other gulls (Kilpi 1989). Predators that represent threat to adult (e.g., Bald Eagle) are mobbed; mobs eagles in pairs even when over large colonies (Lien 1975). Cooperative mobbing rare; observed mobbing Bald Eagle in large flock of 50 gulls, 1 Peregrine Falcon (Falco peregrinus), 5 American Crows (Corvus brachyrhyncos), 1 Northern Harrier (Circus cyaneus), 2 Short-eared Owls (Asio flammeus), and 75 Red-winged Blackbirds (Agelaius phoeniceus; Humphrey 1989). More aggressive protecting chicks than eggs (Butler and Janes-Butler 1982, 1983). If chick gives Shrill Waver, parents (but not other adults) dive at and strike predator while giving Charge Call (TPG; see Sounds: vocalizations, above, for description of calls).