Demography and Populations

Age At First Breeding; Intervals Between Breeding

Males may first breed in fourth year of life, females in fifth (Paynter 1966, Davis 1975). Most breed every year, but some forego breeding during years with poor food supply (Pierotti 1979, 1982).

Clutch

Modal clutch size 3, some birds in poor condition lay 2 or even 1 egg (Tinbergen 1960, Pierotti 1982). Occasional clutches of more than 3 may result from 2 females sharing nest (Shugart 1980) or unusual egg production. Only 1 successful clutch/season, since producing fledged offspring takes minimum 10 wk (typically 15–20 wk; Burger 1984). Up to 2 replacement clutches possible if early clutches destroyed (RJP).

Annual And Lifetime Reproductive Success

Maximum annual fledging success 3, achieved by about 23% of pairs (150/660 pairs in Newfoundland, Pierotti 1979, 1982; 10/43 pairs in New Jersey, Burger 1984). Another 20–30% fledge 2 chicks/yr, 20–30% fledge 1 chick/yr, 15–30% fledge no chicks per year (Pierotti 1979, 1982, Burger 1984). On Great I., Newfoundland, fledging success higher (70–90%) than hatching success (40–85%) (n = 8 subgroups over 2 yr; Pierotti and Annett 1990, 1991). On Clam I., NJ, hatching success (70–80%) slightly higher than fledging success (55–70%) (n = 3 yr; Burger 1984).

Highly variable in lifetime reproductive success, like other birds (Clutton-Brock 1988, Newton 1989); < 50% of fledged chicks survive to breed (Kadlec and Drury 1968). Of these, 30–40% breed only 1–2 times, produce no surviving chicks. Of remaining birds, about half breed 3–4 times, produce 2–4 chicks. Only 10–15% of cohort are highly successful, breeding ≥ 5 yr, producing 10–30 chicks over life span (Paludan 1951, Davis 1975, Pierotti 1979, Coulson and Butterfield 1986). Successful birds in both New England and Atlantic Canada take diet of primarily fish (including fish waste) and marine invertebrates during prelaying and incubation, avoid refuse in diet (Pierotti and Annett 1987, 1990, 1991), and nest in areas without predators (Pierotti 1979, 1982).

Survival of eggs to hatching 70–80%; hatched chicks to fledging 50–70%; fledglings to age of first breeding 50% (Paludan 1951, Paynter 1966, Kadlec and Drury 1968, Pierotti 1979, 1982). Initial breeding attempt crucial step for overall success; probably only 60–70% survive to next breeding season (Paludan 1951, Paynter 1966). In United Kingdom, after second breeding, adult survival about 90%/yr from ages 6 to 18 (Davis 1975, Chabrzyk and Coulson 1976, Coulson and Butterfield 1986), may be as low as 80–85% in North America (Paludan 1951, Paynter 1966, Kadlec 1976), although lower survival rates may represent band loss rather than mortality. Maximum longevity > 30 yr in wild, reportedly > 40 yr in captivity (Terres 1980); 15–20 yr typical in wild (Chabrzyk and Coulson 1976, Coulson and Butterfield 1986).

Avian tuberculosis, internal parasites (Plotz 1980, Vauk et al. 1980). Some chicks show nasal discharge; harsh breathing often associated with death in Newfoundland (Pierotti 1979). Salmonella and botulism implicated as major causes of death in urban colonies. Fleas and ticks (Ixodes spp.) on chicks, especially where mammals (e.g., rabbits) present or recently extirpated from colony (RJP).

Many adult birds die of injuries (broken wings, beaks, etc.). Others shot, poisoned by fishermen. Almost certainly take in contaminants, e.g., chlorinated hydrocarbons, bacterial toxins, during feeding. Problem especially acute in Great Lakes, where many eggs failed to hatch and chicks showed growth retardation and deformities (Weseloh et al. 1979, Becker et al. 1980). Contamination observed in 1950s became severe problem in 1960s and 1970s, but has been alleviated during 1980s as contaminant levels declined (Fox 1990). Some contaminants, e.g., o,p’ DDT and p,p’ DDE, act as estrogen mimics, cause feminization of male embryos, leading to skewed sex ratio in adult population (Fry et al. 1987); results in shortage of adult male gulls and leads to formation of female–female pairs and triads (Pierotti 1981, Fox 1990).

Individuals get tangled in nets and fishing lines. A few taken by predators (owls, raptors, foxes). Most mortality occurs during breeding season (Coulson and Butterfield 1986). Some killed during interspecific territorial conflicts with Great Black-backed Gulls in Newfoundland and Gulf of Maine (Pierotti 1979, McGill-Harelstad 1985).

Natal Philopatry, Dispersal

Natal philopatry high in low-density areas, low in high-density areas. Males much more philopatric than females (Coulson and Butterfield 1986, RJP). At higher latitudes, in colder climates, birds move farther than at lower latitudes (Moore 1976). General southward dispersal responsible for major increases in breeding bird numbers south of Maine since 1900 (Drury and Nisbet 1972, Moore 1976).

Breeding Site Fidelity, Dispersal

Pairs nesting successfully use same breeding territory until male dies or deserts (Tinbergen 1960). Pairs appear to disperse together, possibly accompanied by offspring in late summer and fall; return paired in spring (RJP). Males and females observed together in winter; not known if these are breeding pairs (RJP). Considerable dispersal both southward and offshore in fall and winter (Drury and Nisbet 1972, Moore 1976, Powers 1983).

Home Range

Forages up to 100 km from colony; birds breeding at Witless Bay, Newfoundland, observed feeding on Grand Banks (RJP), more typically forage within 20 km (2-h round-trip) of colony (Drury and Nisbet 1972). Home range dependent on location of reliable food sources and dietary proclivities of individuals (Pierotti and Annett 1991).

Numbers

In 1900, U.S. population only 8,000 pairs, entirely in Maine; around 30,000 in New England by 1935; near 90,000 from Maine to Virginia in mid-1970s (Powers 1983, Andrews 1990); > 100,000 pairs from Maine to Virginia in mid-1980s (Andrews 1990). Last number may represent more accurate censusing rather than actual increase. Current (1990) numbers of pairs break down as follows: Maine 27,000; New Hampshire 350; Massachusetts 35,000; Rhode Island 5,000; Connecticut 3,000; New York 25,000; New Jersey 4,000; Delaware < 100; Maryland 4,000; Virginia 3,000 (Andrews 1990); Gulf of St. Lawrence 11,000 (Chapdelaine and Brousseau 1991). Several thousand pairs breed in Newfoundland and Labrador (Brown et al. 1975). A few thousand pairs breed in Great Lakes (Moore 1976, Blokpoel and Tessier 1991), and a few thousand more pairs probably breed throughout Canadian Arctic south to se. Alaska (Vermeer 1973). Powers (1983) estimated 1 million Herring Gulls offshore from Cape Hatteras to Gulf of Maine in fall. Numbers have stabilized, may even be declining in e. Canada and New England in recent (1980s) years (Hebert 1989). Recent (1980s) increases come mostly from southward range expansion (Andrews 1990).

Trends

See above, and Population Regulation, below.

Population growth limited by availability of suitable nesting areas and natural food sources. Historically, low juvenile overwinter survival and persecution on nesting colonies kept numbers low. Cessation of egging and of killing adults for millinery trade allowed recovery (Graham 1975). Recovery probably also spurred by increased overwinter survival of young birds feeding on refuse. Numbers now declining in New Brunswick, Maine, and Massachusetts as result of egging by locals in Canada and incursion of Great Black-backed Gulls from Labrador to Massachusetts (McGill-Harelstad 1985, Hebert 1988, TPG, RJP). In Newfoundland, early 1990s decline has resulted from crash of capelin stocks (J. Chardine pers. comm.); capelin primary food of Herring Gulls and other seabirds in Newfoundland during chick-rearing (Pierotti 1979, Pierotti and Annett 1987, 1990, 1991).