w_grebe

English

Western Grebe
Aechmophorus occidentalis
This information was scanned from The Birds of British Columbia (Campbell et al.), Volume I, pages 178-181. 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 in western North America from southern British Columbia and the Canadian prairie provinces south to Mexico. Winters from southern coastal British Columbia south to central Mexico and on some inland waters.

Status
Common to very abundant spring and autumn migrant across the southern portions of the province. Locally common to very common along the coast in summer; rare in the interior away from colonies. Very abundant locally on the south coast in winter; rare to locally very common in the interior. Local breeder.

Status Change
No change.

Nonbreeding
The Western Grebe is the most gregarious of our grebes and is often found, locally, in large flocks that are either compact or strung out in a long line. It ranges along the coast and in the interior from the Peace Lowlands and Babine Uplands, south across the province. In the interior, most birds use larger lakes, larger sloughs, and backwaters of rivers. On the coast, sheltered salt and brackish waters are preferred, including bays, inlets, harbours, channels, lagoons, and estuaries. Small numbers are frequently found on slow-moving coastal rivers, large sloughs, lakes, and the open ocean, usually within 2 to 3 km of shore.

Spring migration occurs mainly from late April to early May across southern portions of the province. It is far more pronounced in the interior. In some years, the movement may still be evident in early June, with flocks of more than 2,000 birds. In early spring, large flocks of up to 6,000 birds have been found in areas of spawning Pacific herring. Most grebes have left the coast by mid-May.

In summer, flocks, sometimes hundreds of birds, are found along the south coast throughout the Strait of Georgia and Barkley Sound. Smaller numbers occur on larger lakes in the Thompson and Okanagan valleys and the west Kootenay.

The autumn movement may begin as early as late August but is commonly observed from mid-September to mid-October. At that time, flock sizes may approach 10,000 on the coast and 2,000 in the interior. Numbers build during November and December on the inner south coast where flocks of up to 10,000 birds gather in favourite foraging areas. In the southern interior, flocks of up to 100 birds may winter on larger, ice-free lakes. The centre of winter abundance is the Strait of Georgia.

Migrants have been recorded from sea level to 1,585 m elevation.

Breeding

Nests

Eggs

Young

Historically, the Western Grebe has nested at 7 sites in British Columbia (Table 10), of which only 4 remain active: Shuswap Lake, north arm Okanagan Lake, south end Kootenay Lake, and Duck Lake (Creston). The others have disappeared due mainly to industrial development, recreational activities, and unstable water levels. Since habitat still exists but breeding grebes do not, and since the Western Grebe does not appear to move around a lot, it further supports disturbances as the cause of their disappearance from those areas.

The colony at Williams Lake was active for at least 30 years. It was discovered in 1935 (Munro, J.A. 1939b), reached peak numbers in 1941 (Munro, J.A. 1941b) and was last used in 1964 (23 July - 50 adults with 8 young). On 11 August 1971, Riske (1976) censured Williams Lake and found 15 adults but no young or nests. A colony on Kamloops Lake, was used only once in 1973. The colony at Swan Lake (Vernon) was active for at least 45 years. It was discovered in 1933 (Munro, J.A. 1935a), estimated at 40 pairs in the early 1950s, and last suspected of being active in 1978 (Cannings, R.A. et al. 1987). There is one coastal breeding record but the exact nest site is unknown. On 18 September 1986 an adult was observed feeding 2 half-grown young on Westham Island (J. Ireland pers. comm.). There are 4 isolated nesting records without supporting information, here considered hypothetical (see Forbes 1984). The known breeding population today ranges between 182 and 200 pairs (Table 10). Colonies have been located from 300 to 640 m elevation.

The Western Grebe breeds on medium to large lakes, usually with stands of emergent marsh vegetation (e.g. cattail, bulrush, or reed canarygrass - or flooded shrubs. Other essential requirements for nesting include minimal human disturbance, stable water levels, protection from wind, water deep enough to allow diving, access to open water with substantial fish populations, and a long ice-free period to allow plant growth and breeding (Forbes 1984).

Nests:

Nests are usually built in stands of bulrush or cattail but occasionally at the edge of dense patches of willows (Stirling 1964), in open water over stands of water-milfoils (Forbes 1984), or in a grassy marsh. At the Duck Lake colony, mean density of common cattail stems ranged from 1.4 to 16.1 stems/m2 (Forbes 1984); water depths ranged from 60 to 150 cm.

Nests were large accumulations of vegetation with bases of rotten or decaying vegetation, mostly bulrush, cattail, or reed canarygrass and occasionally sticks. The smaller centre platform was often lined with dry stems of emergent vegetation as well as aquatic plants including water-milfoils, buttercups, filamentous algae, and duckweeds. Outside diameters ranged from 38 to 122 cm, with most between 46 and 61 cm. Nest heights ranged from 5 to 15 cm; the depression from 2.5 to 5 cm deep.

Eggs:

Human disturbance (e.g. anchored fishermen, power boating) and changing environmental conditions (e.g. wind, water levels) make it difficult to determine the natural egg-laying period because of forced re-nesting. Clutches have been reported from 29 April (Munro, J.A. 1939b) to 31 August (incubating - Fyfe and Teeple 1968). Egg-laying is synchronous and probably occurs mostly in late May and early June. Sizes for 433 clutches ranged from 1 to 7 eggs (1E-44, 2E-79, 3E-184, 4E-100, 5E-21, 6E-4, 7E-1), with 66% having 3 or 4 eggs. Bent (1919) reports incubation to be "about 23 days" while Lindvall and Low (1982) give a range of 21 to 28 days with an average of 24 days.

Young:

Young have been recorded from 5 June (Munro, J.A. 1939b) to 31 August. Calculated dates indicate that young could be found as early as 25 May and as late as September (see Fyfe and Teeple 1968). Under normal conditions, most probably hatch in late June and early July. Sizes for 26 broods ranged from 1 to 4 young (1Y-9, 2Y-13, 3Y-3, 4Y-1) with 13 broods having 2 young. Fledging period is unknown.

Remarks
The Western Grebe appears on every "Blue List" from 1973 to 1982 (Tate 1981, Tate and Tate 1982). In the 1980 list, habitat loss was blamed for its current decline, "with more drastic losses predicted in the future" (Arbib 1979). By the 1982 list, the Western Grebe appeared to be "stabilizing at a reduced level" (Tate and Tate 1982). It was delisted to a species of "special concern" in 1986 (Tate 1986).

See Forbes (1985b) for recent studies on feeding ecology.

POSTSCRIPT: On 14 September 1988 a pair of adult Western Grebes, accompanied by 2 less than half-grown, downy young, were seen in a marsh west of the George C. Reifel Bird Sanctuary. On 2 October, presumably the same family group was found in the same area. W.C. Weber (pers. comm.) suggests that occasional pairs probably nest in the brackish marshes off Westham Island.

On 24 March 1989, over 11,000 Western Grebes were counted, in flocks of 4 to 4,000 birds, between Denmarl Island and French Creek (P.W. Martin pers. comm.). The birds were seaward of huge concentrations of gulls, scorers, and loons where Pacific herring were spawning.