Demography and Populations

Age At First Breeding; Intervals Between Breeding

Breeds first in fourth or fifth year of life (Cramp and Simmons 1983). No specific information on age of first breeding for males or females. No data on proportion that breeds every year. Some birds forgo breeding during years of poor food supply (Pierotti 1979).

Clutch

Modal clutch size 3; up to 2 replacement clutches possible if early clutches destroyed. Supernormal clutches reported in museum collections: 0.5% were 4-egg clutches and 0.5% were 6+-egg clutches (n = 189; Conover 1984). On Great I., Newfoundland, mean clutch size 2.88 (n = 16; Pierotti 1979). On Little Duck I., ME, mean clutch size 2.75 (n = 24; Butler and Trivelpiece 1981). On Appledore I., ME, mean clutch size 2.8–2.9; 3-egg clutch achieved by 85–90% of pairs, another 8–12% have 2-egg clutch, 0–3% have 1-egg clutch (Lewis 1982, McGill-Harelstad 1985, TPG). Clutches that were artificially enlarged to 5 chicks showed highly variable results on Sable I., Nova Scotia: broods in 3 enclosures failed within 5 d; remaining broods fledged 1–2 chicks (Lock 1973).

Annual And Lifetime Reproductive Success

Highly variable. Influenced by nesting density (Butler and Trivelpiece 1981), laying date (Erwin 1971, Lewis 1982), food supply (Pierotti 1979), and position in colony (McGill-Harelstad 1985, TPG; Table 2).

Distribution of reproductive success variable. On Appledore I., ME, in 1980, 51% of pairs hatched 3 chicks; 29% 2 chicks, 13% 1 chick, 7% 0 chicks; 23% of pairs fledged 3 chicks; 33% 2 chicks, 22% 1 chick, and 22% 0 chicks. Pairs in peripheral nests hatched more chicks than did pairs in core nests (McGill-Harelstad 1985). In 1991, 21% of pairs hatched 3 chicks, 41% 2 chicks, 29% 1 chick, and 9% 0 chicks; 2% of pairs fledged 3 chicks, 27% 2 chicks, 29% 1 chick, and 43% 0 chicks (TPG). Mean number of fledglings per nest of pairs with Herring Gull neighbor (1.43 ± 0.25 SE; range 0–2, n = 10) is greater than of pairs with several conspecific neighbors (0.75 ± 0.14 SE; 0–2, n = 27) or at edge of colony (0.6 ± 0.27 SE; 0–3, n = 18; TPG).

No data on lifetime reproductive success.

Number Of Broods Normally Reared Per Season

One brood/yr. Can lay replacement clutch if first clutch is destroyed (Belopol’skii 1961).

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

No data.

From fledging to 6 yr old, average 20% annual mortality (Flegg and Morgan 1976). No data on age-specific mortality or age-specific recruitment; no data on sex-specific or age-specific immigration and emigration rates. Longevity reported as >19 yr in wild, >17 yr in captivity (Terres 1980).

Internal parasites common and numerous (nematodes: Cosmocephalus obvelatus and Capillaria contorta [esophageal], Paracuaria tridentata and Tetrameres fissispina [proventricular]; Plotz 1980). Up to 4 trematode species, 2 nematode species, and 8 cestode species found in 1 individual in Newfoundland (Threlfall 1968b). In Wales, 20% of intestines examined were infected with the trematode Cryptocotyle lingua, and 3% with the trematode Microphallus similis; 55% of gallbladders were infested with the gymnophallid Gymnophallus deliciosus (Harris 1964c). Also hosts Reighardia sternae (Pentastomida); 4 of 50 individuals parasitized, 1 juvenile infected by 25. Female Reighardia recovered from air sacs and males from the body cavity; tapeworm (Cestoda) infestation may confer natural immunity against Pentastomids (Böckeler and Vauk-Hentzelt 1979). Definitive host of avian blood fluke (Austrobilharzia variglandis), source of marine cercarial dermatitis; along with Herring and Ring-billed gulls in Connecticut, showed higher prevalence (85–93%) and intensity (12–35 male worms per individual) than in cormorants or geese (Barber and Caira 1995).

Salmonellae (11 serotypes, usually Salmonella virchow) detected in 10.7% of 560 individuals (Fricker et al. 1983). Examination of 1,242 fecal samples revealed that 12.9% have salmonellae (27 serotypes); counts higher near sewage outfalls. Individuals show no sign of disease, but may transmit to livestock by roosting on grazing lands (Fenlon 1981).

Strong but circumstantial evidence of botulism in sw. Wales; incidence correlated with use of black garbage bags. Adults exclude juveniles at landfills, and only adults are found with botulism (Sutcliffe 1986). Type C botulism (Clostridium botulinum) found in 4,040 of 5,994 birds, mostly gulls, found dead in summer and autumn of 1975 in Britain (Lloyd et al. 1976). Fleas and ticks present and feeding on chicks (Roy et al. 1986); biting lice (Saemundssonia lari) present on many individuals (Threlfall 1968b).

See Behavior: predation, above. Chicks die of injuries, are pecked or eaten; some die during pipping, starve, or succumb to exposure (Lock 1973, McGill-Harelstad 1985, TPG). Chick carcasses are eaten during chick-hatching period and fed to young (Lord and Burger 1984).

Many adult birds die of injuries (broken wings, beaks, etc.), some by becoming tangled in nets. Adults killed by striking aircraft (Dolbeer et al. 1993); fewer confirmed collisions than in Herring or Ring-billed gulls (Dolbeer and Bucknall 1997). Most birds die during breeding season. Some are killed during intraspecific territorial conflicts at dense colonies (Isles of Shoals, Gulf of Maine; McGill-Harelstad 1985). Carcasses are rarely eaten by conspecifics before chicks hatch; always eaten during last few weeks before chicks fledge (Lord and Burger 1984).

Initial Dispersal From Natal Site

General southward dispersal (Southern 1980). No data on distance between natal site and site of first breeding.

Fidelity To Breeding Site And Winter Home Range

No data for North America. In Belgium, high site fidelity: 90% of winter recoveries are at banding sites (refuse dumps) or within 50 km (Vandenbulcke 1989).

Dispersal From Breeding Site Or Colony

Adults are sedentary; most remain north of 36°N. Mean distance between ringing and recovery sites is <300 km Apr–Sep (maximum 583 km in Feb) and <200 km Jun–Aug (minimum 184 km in Jul; Southern 1980). In Britain, adults are mainly sedentary near breeding colonies. First-year birds migrate <160 km; after movements of first year, return to areas near parent colonies (Harris 1962). In Finland, 3% of adults banded were recovered beyond 500 km (Kilpi and Saurola 1983).

Home Range

May forage up to 100 km from colony; birds breeding at Witless Bay, Newfoundland, were observed feeding on Grand Banks (R. Pierotti pers. comm.). More typically forages within 20 km (2 h round-trip) of colony. Home range depends on location of reliable food sources and on dietary proclivities of individuals.

Numbers

Recent census data in Table 3 .

Trends

Increases come mostly from southward range expansion (Andrews 1990). In Newfoundland, breeding numbers increased 35-fold on Funk I. from 1956 to 1987 and doubled to 250 pairs on Witless Bay islands from 1970 to 1979 (Montevecchi and Tuck 1987). From Maine to Virginia, increased from 17,405 nesting pairs at 349 sites in 1977 to 30,780 pairs at 397 sites in 1984 (Andrews 1990); 1994–1995 regionwide survey estimated 38,642 nesting pairs (B. Hoover pers. comm.). From 1926 to 1965, increased in U.S. about 17%/yr (Nisbet 1978).

At Isles of Shoals, ME, increased from 86 pairs in 1944 to peak of 2,900 breeding pairs in 1989 (Borror and Holmes 1990). In Massachusetts, number recorded in 1994–1995 survey (15,000 pairs; I. C. T. Nisbet pers. comm.) was up from 1984 census (10,768 pairs; Andrews 1990); at Monomoy National Wildlife Refuge, Chatham, MA, increased from 5,000 pairs in 1984 to 8,200 pairs in 1990 (Cavanagh 1992). In 1983, 2,013 pairs on Gardiners I., NY, alone—an important colony (2,600 pairs by 1985; Andrews 1990) in U.S. and one of the largest in North America (Buckley and Buckley 1984). On Long I., NY, peaked at 1,938 pairs in 1974. In New Jersey, peaked at >250 pairs in 1983. In Maryland, peaked at 50 pairs in 1982. In Virginia, peaked at 125 pairs in 1983 (Buckley and Buckley 1984).

On 8 colonies on north shore of St. Lawrence River, decreased from 2,966 in 1940 to 1,420 in 1945 because of control program; increased from 998 in 1950, to 1,562 in 1972, to 1,883 in 1988 (Chapdelaine and Brousseau 1991). Overwintering populations on Lakes Huron and Ontario increased in 1940s and 1950s, fluctuated from 1954 to 1974, and increased dramatically in 1976 (Angehrn et al. 1979). On south shore of Lake Erie, counts of early-winter populations at 4 sites increased an average of 7.7-fold from 11.2 (range 2–30) in 1950–1959 to 85.7 (range 30–176) in 1975–1984 (Dolbeer and Bernhardt 1986).

First recorded breeding on Little Haystack I. in Lake Huron, Ontario, in 1954; regularly nested on 2 islands in e. Lake Ontario in 1960s and 1970s (Angehrn et al. 1979, Peck and James 1983). During 1981–1985, single pairs were confirmed at 6 islands in Lake Ontario and 1 island in Lake Huron (Blokpoel 1987). Between 1988 and 1991, 12 breeding attempts were reported at 8 sites in Lake Huron, including 2 pairs at Goose I., at tip of n. Michigan (Ewins et al. 1992).

Has not increased (about 15 pairs in 1997; J. C. Johnston unpubl. data) on Kent I., New Brunswick, during time of Herring Gull decline. Since 1984, colonies in e. Maine have declined markedly (I. C. T. Nisbet pers. comm.); populations at Isles of Shoals appear to have leveled off (A. C. Borror unpubl. data, TPG). In Massachusetts, population may have increased or stabilized in 1990s (P. M. Cavanaugh pers. comm.). Breeding populations stable and low in Great Lakes; overwintering populations still increasing.

Historically, persecution on nesting colonies kept numbers low. Cessation of egging and of killing of adults for millinery trade allowed recovery. No data on juvenile overwinter survival; recovery generally attributed to increased overwintering survival of young birds feeding on fisheries waste and garbage. In Newfoundland, population declined during 1990s as result of crash of capelin stocks, offshore dumping of fisheries waste, and fishing moratorium imposed in 1992 (J. Chardine pers. comm.).