Behavior

Walking, Hopping, Climbing

On land, typically walks or runs with legs alternating. Can jump or hop onto perches by opening wings, using single wingbeat for elevation, and pushing off with legs. Also hops down with wings partially spread. In agonistic charges, runs with wings partially upraised. Also runs to take off for flight. Does not use hopping as form of locomotion. Does not climb vertical objects.

Flight

Adjusts wingbeat and orientation to wind to regulate speed. Spends considerable portion of flight time gliding or soaring with outstretched wings (Fig. 5). Dives and swoops by adjusting angle of wings. When joining feeding groups on water, often descends by flapping wings and flying in rapidly diminishing circles (Hoffman et al. 1981). Attacks terrestrial predators using steep dives, strikes at predator with wings, feet, (rarely) beak.

Swimming And Diving

Swims on surface of water using paddling motion of legs for propulsion. Can dive either from surface or short distance above water, but cannot reach depths >1–2 m below surface because of high degree of buoyancy (Tinbergen 1960, RJP).

Preening, Head Scratching, Bathing, Anting, Etc

Does not ant. Bathes regularly resting on water, ducking head and body parts under water 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, rubs secretion on feathers. Head scratching involved in preening (leg under wing). Preening occupies 6% of 24-h day (Amlaner 1983).

Sunbathing, Thermoregulation

See above, Metabolism and Temperature Regulation.

Sleeping And Roosting

During breeding season, sleeps or rest-sleeps about 10 h (42% of 24-h day; Amlaner 1983). During daylight, sleeps in 1- to 15-min bouts. At night, sleeps in 45- to 300-min bouts. Sleeps with head resting on breast, legs folded underneath body; some individuals sleep while perching on 1 leg with other leg folded against body. Deeply sleeping birds tuck head under wing along back. Males and females sleep similar amounts of time/d (Amlaner 1983). Birds sleep 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, garbage dumps. Sleeps and preens on specific areas, referred to as “clubs,” on breeding colonies (Tinbergen 1960).

Daily Time Budget

Male and female time budgets vary among habitats and between years (Morris 1987, Pierotti 1987a). Males spend more total time on territory and less time incubating than females, who typically spend 85–90% of total time present on nest (Pierotti 1987a). Male present, and incubates, more often in mid-morning and late afternoon. Female present, and incubates, more in early and mid-afternoon and at night. Male typically leaves to forage before dawn, returns mid-morning, when female leaves to forage. Diurnal pattern similar during chick-rearing; male and female present similar amounts of time, except in habitats where Great Black-backed Gulls nest, where males spend more time present guarding chicks from attacks (Pierotti 1987a).

Adults spend most time on territory sleeping or resting. Amount of time spent sleeping and resting varies from 70–75% during incubation to <50% during later stages of chick-rearing (Amlaner 1983, Morris 1987). Outside breeding season, forage 2–3 h/d; rests, sleeps, preens remainder.

Physical Interactions

Inter- and intraspecific intruders chased, both in air and on ground, and may be attacked. Attacks between neighbors begin with jabbing at opponent with beak, grabbing opponent by tail, wing, beak, rarely by neck. Birds gripping each other by beak engage in extended pulling bouts, which may last several minutes (Tinbergen 1960). If individual loses balance during pulling contest, it is struck with wings or pecked. Attacks on intruders usually begin with charge (see below, Communicative interactions). Birds retreating from opponent often give Shrill Waver or Alarm Call (see Vocal array). Birds also pursue retreating opponents by flight, or on ground with wings upraised. Males engage in fights and pursuits much more often than females do (Tinbergen 1960, Pierotti 1987a).

Adults attack chicks running across territory. Chicks typically grabbed by head and shaken. Smaller chicks may be grabbed by body and pummeled or thrown. Intruding conspecific chicks may be killed but are almost never eaten (Pierotti and Murphy 1987, Pierotti 1991). Such infanticidal attacks should not be referred to as “cannibalism,” which is engaged in by only a few males (sometimes none) in any single colony. Adults also attack first few chicks to fledge in area. Attacks involve repeated swoops, blows struck with wings, feet, bill; sometimes several adults involved. Behavior strongly resembles attacks directed toward raptors or herons flying over colony and may result from mistaken identity.

Communicative Interactions

Complex repertoire, involving at least 11 separate displays. Several displays closely linked with vocalizations after which they are named (see above, Vocal array). Some displays have multiple context-dependent functions (Beer 1975, Hand 1985). Therefore, displays not subdivided into threat and appeasement, although these functions are discussed.

Upright Posture. Approaches slowly in rigid posture with neck stretched upward and forward with head pointed slightly downward (Tinbergen 1960; see Fig. 6). In high-intensity forms, wings lifted so they stand out from body, increasing apparent size. Wings also positioned to strike blows. Given significantly more often by males than females. Directed at neighbors, intruding conspecifics. Often leads to Grass-pulling (see below) or Long Calling 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. Intruders almost invariably fly in response to Charge. Intruders that persist are often pursued through air. Intruders that do not fly away are attacked (see above). Males more likely to Charge, especially against male opponent. Females Charge primarily female and immature opponents (Pierotti 1987a).

Alert Posture. Like Upright, but neck held back, so appearance less threatening (Tinbergen 1960). Often given by target of Upright. Also shown in presence of predator prior to flight.

Oblique Posture. Associated with Long Call. Bird lowers head toward ground (in extreme cases head almost horizontal under breast), produces Long-call Notes. Throws head back over scapulars, stretches neck out fully with mouth wide open (body forms oblique angle with substrate, hence name) while emitting series of call notes (Tinbergen 1959, 1960; also see Fig. 4). Given in several contexts: (1) after bout of aggression over territorial boundary, (2) when mate returns from absence, (3) when neighbor returns from absence, (4) at birds flying over territory. Oblique Posture without Long Call functions as threat when shown by bird stretching neck toward opponent across boundary.

Silent Squat. Bird crouches with breast touching or just above substrate, rear end elevated. Head in position similar to Upright. Often alternates with bill-jabs, Grass-pulling. Directed only at neighbors while face to face. Given more often by males than females (Pierotti 1979).

Grass-pulling. During territorial disputes, 1 or both opponents take vegetation in beak, brace feet wide apart, pull vigorously at vegetation (Tinbergen 1960). Usually performed while facing neighbor opponent < 1 m away. Rarely shown by females (Pierotti 1987a). Functions as high-intensity threat. Similar posture taken by bird grasping opponent by wing, tail, or beak during fight (Tinbergen 1960). May be displacement activity.

Choking. Display accompanying vocalization. Bird lowers breast, bends legs, points head down, and depresses hyoid bone, giving throat “swollen” look. Bird(s) perform rhythmic jerking movement with head, producing deep huoh-huoh-huoh call (Tinbergen 1960). Typically given by pair in tandem during territorial boundary disputes. Only agonistic display performed as often by females as males. Virtually identical display directed at partner when identifying nest scrapes and during nest exchanges. In these cases given by bird on nest or over scrape. Display appears to indicate strong motivation to occupy specific location (Hand 1979). May be derived from incomplete regurgitation (Beer 1975).

Mew-call Posture. Similar to Upright, except neck more arched and head lowered with mouth open so Mew Call can be produced. Functions to attract mate or chicks when given after returning to territory. In these instances, Mew-call Posture with arched neck often precedes regurgitation of food for mate or offspring. Also shown in territorial disputes, when intruder lands on territory. In these cases appears to function as high-intensity threat.

Head-tossing. Associated with Begging Call. Bird hunches neck so head drawn close to body (Fig. 7). Head repeatedly flicked upward while Begging Call (Klee-ew) given with each toss. Appears to stimulate regurgitation by male when given by female, or by parent when given by chick or juvenile. Given by both members of pair in tandem prior to copulation. May function as agonistic display in juveniles, because adults retreat from Head-tossing juveniles. More likely that adult is unwilling, or unable, to regurgitate and simply moves away from juvenile.

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

Anxiety Posture. Like Facing-away, but with wings slightly raised, neck stretched farther forward, body and head oriented away from other bird (Tinbergen 1960). Given by intruder in response to Upright Posture or Charge. Probably preparatory or intention movement for flight.

Territoriality

Maintains breeding territory on colony during breeding season; maintains only personal space (< 1 m) on roosting areas during both breeding and nonbreeding seasons. Territory established by male, defended by pair.

Nature and extent of territory. Breeding territories areas of substrate, defended against conspecifics or congenerics. Territory size depends on nature of substrate and heterogeneity of terrain. Heterogeneous habitats permit smaller areas. On Great I., Newfoundland, internest distances averaged about 4 m in heterogeneous rocky habitats, 6–7 m in tussock meadows with small trees, 8–9 m in open meadows (Pierotti 1982). On Clam I., NJ, nearest-neighbor distance averaged 4.5 to 5.0 m with range 2.3–8.3 m (Burger 1984). Territory size on Clam I. averaged 38.9 ± 14.8 m²with range 16.0–72.6 m². Size of defend-ed area changes over breeding season: largest during chick-rearing, smallest during incubation, intermediate during prelaying (Burger 1984). Changes relate to value of territory and settling pattern. During earliest stage, fewer pairs settled and defended areas larger. Incubating pairs less aggressive; new pairs can then establish (Burger 1984, Pierotti 1987a). When chicks hatch, parents much more aggressive, attack all intruders in area, strongly defend boundaries against neighbors (Pierotti 1987a). Territorial boundaries quite flexible, depending on context, with small “unique territory” defended against all birds other than pair and offspring, “primary territory” defended only against neighbors, “secondary territory” defended against intruders (Burger 1984). Last may contain portions of primary, but not unique, territories of other pairs. Males defend all 3 categories of territory; females defend primarily unique territory (Pierotti 1987a).

Manner of establishing and maintaining territory. Prior to breeding season, males defend areas of breeding colony. If male already paired, mate helps defend area but does not help establish initial territory. If male not paired, he may be joined by unpaired females, whom he will either court or drive off (Tinbergen 1960). Females defend and maintain territory when male absent (Pierotti 1987a). When male present, he performs most defense and maintenance. Established pairs typically return to same territory as long as they remain paired. If male dies or abandons, female must find new mate and territory. If female dies or abandons, male remains on same territory (Pierotti 1980).

Interspecific territoriality. Herring Gulls nests in mixed-species colonies with other gulls, terns, skimmers, alcids; rarely with cormorants and gannets. Only defends territories against other gulls: Great Black-backed, Ring-billed, and Laughing gulls along Atlantic Coast and Great Lakes; Glaucous-winged Gull in California; Glaucous Gull in Canadian Arctic or Alaska. Often supplants smaller species, but is supplanted by larger species.

Winter territoriality. Defends feeding areas on beach or intertidal against conspecifics and congenerics (Drury and Smith 1968). Some individuals or pairs defend feeding territories throughout year (I. C. T. Nisbet pers. comm.). In warmer latitudes, some birds may remain on and defend both breeding and feeding territories throughout entire annual cycle.

Dominance hierarchies. Dominance context specific. Adults typically dominant over juveniles or immatures. Males may dominate females during feeding and boundary disputes; females win conflicts over choice of nest site and incubation (Hand 1985).

Individual Distance

See Territoriality, above.

Mating System And Sex Ratio

Almost exclusively monogamous. Rare instances of “polygyny,” where 1 male and 2 females occupy territory and incubate either single nest or double nests (Shugart 1980, Fitch and Shugart 1983). Secondary females achieve little or no breeding success. Occasional accounts of multiple females, promiscuous matings, and female-female pairs in gulls probably result from slightly skewed sex ratios favoring females (Pierotti 1980, Burger and Gochfeld 1981). Males losing mates can replace them quickly, whereas females losing mates cannot replace them; suggests more adult females than males in most populations (Pierotti 1980, 1982, Burger and Gochfeld 1981). At least 2 parents necessary to successfully rear offspring because eggs left alone in nests often eaten, and offspring left alone often attacked or killed (Burger 1984, Morris 1987, Pierotti 1987a).

Courtship Displays And Mate-Guarding

No displays specific only to courtship (Tinbergen 1960). Females typically approach males in hunched Head-tossing (begging) posture (Fig. 7), producing Begging Call. Male responds by assuming (1) Upright Posture or (2) Mew-call Posture and Mew-calling. Female circles male, increasing begging intensity if he Mew-calls. Male may either Choke or regurgitate and feed female (Tinbergen 1960). If male regurgitates food and female accepts it by eating, often leads directly to copulation. Mate-guarding reported to be most intense in week prior to laying (Morris and Bidochka 1983).

Copulation

Male and female Head-toss together repeatedly. Male moves behind female, jumps on her back with wings outspread. Female continues Head-tossing while male begins Copulation Call (see Vocal array). After completion, male jumps off, shakes, preens. If female does not eat food regurgitated by male, she may prevent him from mounting by walking away. If male loses balance or takes too long achieving cloacal contact, female may walk out from under him after he begins Copulation Call (RJP).

Duration And Maintenance Of Pair Bond

Pair bonds maintained as long as both members of pair remain alive (Tinbergen 1960). Major factor leading to rupture of pair bond is failure to hatch eggs, either because male does not provide adequate food to female during egg formation or because male and female do not synchronize activities so eggs left unattended (often eaten) (Morris 1987, RJP). Only 8 of > 300 pairs on Great I., Newfoundland, broke up (both members of pair observed after breakup) (RJP).

Extra-Pair Copulations

Males whose mates have completed laying solicit copulation from neighboring females (MacRoberts 1973, RJP). Male may attempt to force copulation on incubating females. No forced copulation attempt ever observed to result in successful transfer of sperm (MacRoberts 1973, RJP).

Degree Of Sociality

Although species nests colonially, most social interactions between neighbors agonistic. Appear to nest as far apart as limited space allows (Pierotti 1979, Coulson 1991). If sufficient habitat available, nest solitarily, breeding success high. Away from breeding colony, loaf and roost together in groups, forage in loose groups that aggregate quickly when prey located (Hoffman et al. 1981, Pierotti 1988). Foraging groups often include other species, including kittiwakes, cormorants, shearwaters, alcids, dolphins, whales (Hoffman et al. 1981, Pierotti 1988).

Play

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

Nonpredatory Interspecific Interactions

Mixed-species foraging, loafing, and roosting groups (see above). Eiders and puffins benefit from Herring Gulls’ vigilance and attacks on predators (Pierotti 1983, Gotmark 1989). Interspecific territoriality with other gull species (see above, Spacing: Territoriality).

Kinds Of Predators

On adults: Bald Eagle (Haliaetus leucocephalus), Peregrine Falcon (Falco peregrinus), Gyrfalcon (F. rusticolis), Great Horned Owl (Bubo virginianus), red fox (Vulpes vulpes), domestic dog (Canis lupus familiaris), harbor seal (Phoca vitulina), gray seal (Halichoerus grypus), various sharks (e.g., Charodon). On chicks: conspecific adults (rare), Great Black-backed Gull (often), other sympatric gulls, Northern Harrier (Circus cyaeneus), Great Horned Owl, Short-eared Owl (Asio flammeus), Common Raven (Corvus corax), Black-crowned Night-Heron (Nycticorax nycticorax), Great Blue Heron (Ardea herodias), red fox, domestic dog, raccoon (Procyon lotor), domestic cat (Felis catus), mink (Mustela vison). On eggs: conspecifics, other sympatric gulls, ravens and crows (Corvus spp.), red fox, mink, raccoon, rats (Rattus spp.) (Tinbergen 1960, RJP).

Response To Predators

When predator first sighted, Herring Gulls give Alarm Call. If predator approaches, give Warning Call, take off, and circle overhead. Mob flying predators (hawks, ravens) by pursuing through air giving repeated Long-call Notes (keow), dive and strike at predator with beak and feet. Dive at terrestrial predators, strike with feet, wings, rarely with beak. Some predators representing threat to adult, e.g., Peregrine Falcon, avoided. More aggressive protecting chicks than eggs. If chick gives Shrill Waver, parents (but not other adults) dive at and strike predator while giving Charge Call while neighbors emit intense Long-call Notes (RJP).