gw_gull

English

Glaucous-winged Gull
Larus glaucescens
This information was scanned from The Birds of British Columbia (Campbell et al.), Volume II, pages 264-271. Volumes I, II and III of The Birds of British Columbia can be ordered electronically at: orders@ubcpress.ubc.ca from UBC Press in Vancouver, British Columbia.

Range
Breeds from the southern Bering Sea and southern Alaska south along the Pacific coast to northwestern Washington; also on the Commander Islands. Winters throughout the breeding range south along the coast to southern Baja California; also on the Pacific coast of Asia south to Japan.

Status
Along the coast, a very abundant spring and autumn migrant and very common to very abundant summer visitant. A very common to abundant winter visitant on the north coast, including the Queen Charlotte Islands; very abundant on the south coast including the Fraser Lowlands. In the central-southern interior, a very rare visitant; casual in northeastern British Columbia. Widespread breeder along the coast.

Status Change
No change.

Nonbreeding
The Glaucous-winged Gull is widely distributed along the coast. It prefers nearshore areas, but regularly visits fishing vessels well offshore, and may be partially pelagic in some seasons (Sanger 1970, 1973a; Wahl 1975). In the interior, it has been recorded from Anderson Lake, Kamloops, and Squilax south through the Okanagan valley and in widely separated locations in the northeast. It occurs from sea level to 1,200 m elevation.

The Glaucous-winged Gull is found in all coastal habitats at all seasons. It is the "sea gull" of the coast. It occurs in extremely large numbers in bays, harbours, estuaries, and rivers where spawning Pacific herring, salmon, and eulachon are found. It is very gregarious and often congregates with other marine-foraging birds over schools of sandlance and Pacific herring (Porter, J.M. 1980). It roosts at night in large flocks on sheltered bodies of water along the coast, including bays, inlets, rivers, islands, and log booms, and on larger freshwater lakes. Man-influenced habitats used along the coast include garbage dumps, city parks, athletic fields, school yards, airports, agricultural fields, buildings, and structures along waterfronts. In the interior, the Glaucous- : winged Gull has been found at garbage dumps, lakes, river mouths, and city parks. Even though the species is present along the coast in numbers throughout the year, there is a definite migration. In; spring, the movement generally occurs between late March and early May, and in autumn between late September and late October. Most large spring and autumn concentrations are related to herring and salmon spawning sites, respectively. In summer, flocks are usually small except near colonies and garbage dumps. Tagging and banding studies by Drent and Ward (1970) and R.W. Butler et al. (1980) indicate that a portion of the breeding population, mostly immatures, shifts southward along the coast during winter. Many of these gulls collect in the Vancouver region and Fraser River delta where 70% to 80% forage at refuse sites (Ward, J.G. 1973). For example, results of Christmas counts at 13 locations in the Strait of Georgia and Juan de Fuca Strait in 1980 produced 101,968 Glaucous-winged Gulls, 72% of which were tallied at 5 locations in the Fraser Lowlands. At dusk they move to night roosts in the vicinity of Burrard Inlet, Steveston, Boundary Bay, and Sapperton. These winter roosts are active from October to March. Peak movements (65,100 in 1970) - occur in late November (Campbell et al. 1972a).

Breeding

Nests

Eggs

Young

The Glaucous-winged Gull breeds along inner and outer coastal waters from Race Rocks off southern Vancouver Island north to Zayas Island, including the Queen Charlotte Islands. It has also been found breeding on Fulmore Lake, a freshwater lake near Port Neville (Rodway In press). Similar situations have previously been reported (Wahl 1972; Weber, J.W. and Fitzver 1986). It breeds from near sea level to 90 m elevation.

The Glaucous-winged Gull is primarily colonial but frequently nests singly. Preferred sites are on small, offshore islands, less than 25 m high and ranging in size from 2 to 10 ha. All major colonies are on islands less than 25 ha in size and 100 m in height. Colony sites are usually treeless, often bare, or with large patches of grasses, herbs, or shrubs. On large forested islands, small numbers of gulls use bare, rocky headlands and cliffs.

During the past 2 decades an increasing and expanding Glaucous-winged Gull population has forced gulls to colonize new habitats, often near urban environments (Campbell 1975c; Hooper, T.D. 1988). The first nests on the roofs of buildings were reported by Oldaker (1963a) and Sanford (1974) at Vancouver. In 1971, the first mainland site was established on a man-made jetty (Campbell 1975c) and this site had expanded along the Vancouver waterfront by 1976 (Poynter 1976). By 1984, small colonies had become established on the support beams of bridges in Vancouver (Hobson, K.A. and Wilson 1985). By 1986, the nesting population in downtown Vancouver was estimated at 500 pairs (Vermeer et al. 1988).

In Victoria, T.D. Hooper (1988) located 99 nests on the roofs of buildings in numbers ranging from 1 to 9 per roof. Other urban sites, often used by isolated pairs, include derricks, light beacons, barges, wooden pilings, log booms, large trees, building ledges, a control house of an operating crane, a drydock, a water tower, and a marine buoy.

During the past 50 years, the Glaucous-winged Gull population in British Columbia has increased about 3.5 times (Drent and Guiguet 1961; Campbell 1975c; Verbeek 1986). In the 15 year period from 1960 to 1974, the population nearly doubled in the Strait of Georgia and Juan de Fuca Strait (Campbell 1975c; Verbeek 1986). The total breeding population in British Columbia, as of 1987, is estimated at 25,000 pairs.

The centre of the breeding population is situated in the vicinity of Vancouver Island where 56% of all colonies are located. Populations of Glaucous-winged Gull colonies (in pairs) from 4 geographical areas are: the Strait of Georgia (13,004 at 72 sites in 1986-Vermeer and DeVito 1989), the west coast of Vancouver Island (6,828 at 53 sites in 1986), the Queen Charlotte Islands (2,600 at 85 sites in 1986-Rodway 1988), and Queen Charlotte Strait (844 at 22 sites in 1987-Rodway In press).

In Alaska the breeding population is estimated at 133,000 pairs and in Washington it is about 18,500 pairs (United States Department of the Interior 1988; Speich and Wahl 1989). Nests: Most nests (99%; n=68,077) were on islands or rock islets. The rest were on the mainland, on waterfront buildings or other man-made structures. Some were in mixed colonies of other ground-nesting species such as Double-crested, Brandt's, and Pelagic cormorants, and Common Murres.

Nests:

Nests were usually situated on the ground on rock surfaces, with or without vegetation, along the upper reaches of sandy beaches, among driftwood, on cliffs, and on headlands. Nesting substrates for 81 nests on the roofs of buildings in Victoria included gravel, tar paper, asphalt shingles, wood, concrete, and metal (Hooper, T.D. 1988). A few nests were in coniferous trees such as Silka spruce, Douglas-fir, and western redcedar. Heights of tree nests ranged from 2 m (on a branch) to 18 m in a Bald Eagle nest; on buildings and other structures nest heights ranged from 4 to 61 m. Nests were usually meagre to substantial saucers or mounds, with shallow to deep cups, often with large bases. Occasionally, eggs were laid on bare rock, in sand or dirt, or on roofs of buildings without nesting materials. Materials are usually available in the immediate vicintiy of the nest, that is, within the territory (Patten 1974). Some adults in British Columbia, however, have been known to fly up to 10 km from colonies in search of nesting material. Nests were composed variously of grasses, mosses, seaweeds and other marine vegetation, plant stalks, rootlets, twigs, driftwood, feathers, bark, leaves, and man-made material such as string, plastic bags, pieces of fishing net, and paper. Lining materials included grasses, feathers, leaves, cones, rootlets, conifer needles, mosses, lichens, and bark.

Occasionally, nests were built entirely of seaweeds or eel-grass. The dimensions for 366 nests ranged as follows:

outside diameter 20 to 86 cm

inside diameter 10 to 36 cm

outside height 4 to 41 cm

bowl depth <1 to 20 cm

Eggs:

Dates for 68,077 clutches ranged from 30 April to 20 August with 78% recorded between 5 and 26 June. Exceptionally bad weather can delay the timing of egg-laying (Verbeek 1986). Clutch size ranged from 1 to 5 eggs (1E-9,681, 2E-20,632, 3E-37,631, 4E-125, 5E-8), with 55% having 3 eggs. Gulls will lay a second clutch if the first is destroyed, but it will usually contain fewer eggs. The incubation period for Mandarte Island gulls was about 27 days (Vermeer 1963; Verbeek 1986), based on the time from laying of the "c" egg to its hatching.

Glaucous-winged Gull eggs have also been found in active and inactive nests of Double-crested, Brandt's, and Pelagic cormorants, Great Blue Heron, Canada Goose, Bald Eagle, Black Oystercatcher, and Northwestern Crow.

Young:

Dates for 13,178 broods ranged from 8 June to 8 September with 68% recorded between 7 and 25 July. Calculated dates indicate that young could be found as early as 3 June. Brood size ranged from 1 to 4 young (1Y-2,133, 2Y-4,587, 3Y-6,432, 4Y-26) with 84% having 2 or 3 young. Fledging period ranges from 37 to 53 days with an average of 44 days (Vermeer 1963).

Remarks
More specific information on the breeding biology and ecology of the Glaucous-winged Gull throughout its range in western North America can be found in Henderson (1972), McMannama (1951), Patten (1974), Vermeer (1963), J.G., Ward (1973), and Verbeek (1986).

This species interbreeds with the Western Gull in Washington (Scott, J.M. 1971; Hoffman et al. 1978) and British Columbia (Pearse 1946) and with the Herring Gull in Alaska (Williamson and Peyton 1963; Fatten and Weisbrod 1974) and British Columbia (Merilees 1974b). This interbreeding creates a continuous gradation in primary feather pigmentation and abnormal plumages (see also Pearse 1947; Vermeer et al. 1963). Verbeek (1979) discusses timing of primary moult for this species in the province.

Glaucous-winged Gull chicks have been banded in British Columbia at various south coast colonies on and off since 1921 (Pearse 1923). Analysis of banding returns have shown that most Glaucous-winged Gulls disperse southward along the west coast of North America in autumn. Early reports by Pearse (1923) and Woodbury and Knight (1951) indicate that young Glaucouswinged Gulls disperse more widely, up to 2,050 km, than adults. This is supported by Gabrielson and Jewett (1970) and Baltz and Morejohn (1977). Recently, however, Butler et al. (1980) have shown that "although first-year gulls dispersed farther than older age classes, the mean dispersal distance between age classes showed little difference."

The most significant conclusion from banding returns is the seasonal shift in mortality of immatures that has occurred over the years as an apparent consequence of the increased gull population.

The time of peak mortality has changed in the following manner:

1938 to 1941 January (Woodbury and Knight 1951)

1959 to 1963 November through February (van Tets 1968)

1966 to 1969 mid-winter

1975 to 1979 late summer and autumn

Verbeek (1986) suggests that the "food supply in the early autumn is no longer adequate to meet the demands of the adults and the recently fledged young, the latter losing out in the resulting competition".

First year mortality is about 60% (Butler, R.W. et al. 1980), and gulls rarely live beyond 15 years. The 5 oldest birds recorded from British Columbia were 20 years 62 days (Campbell 1968a), 21 years (Vermeer 1963), 25 years 6 months (Campbell 1975a), 29+ years (Wakefield 1987; K.S. Wakefield pers. comm.), and 32 years (J.B. Waddell pers. comm.; Brown, B. 1985

POSTSCRIPT: In 1988 the total breeding population was estimated at 28,575 pairs, 49% found in the Strait of Georgia and 25% along the west coast of Vancouver Island. There are 331 nesting sites known in the province.