In British Columbia, colonial-nesting freshwater birds are familiar and important parts of our avifauna. Five species of colonial-nesting birds are discussed in this manual: Red-necked Grebe (B-RNGR, Podiceps grisegena), Eared Grebe (B-EAGR, Podiceps nigricollis), Western Grebe (B-WEGR, Aechmophorus occidentalis), American White Pelican (B-AWPE, Pelecanus erythrorhynchos), and Great Blue Heron (B-GBHE, Ardea herodias).
Red-necked Grebes are widespread breeders in the interior and common along the coast during winter. Eared Grebes are relatively inconspicuous birds that breed in shallow interior marshes, in very large colonies at some sites, and winter mainly in the United States. Western Grebes breed at four sites in British Columbia, but are very abundant in the southern Strait of Georgia during winter. The American White Pelican, a highly recognizable species, is seldom seen in British Columbia, except in the Chilcotin where it breeds. The Great Blue Heron nests in trees and forages mainly along intertidal areas, edges of freshwater marshes, ditches, and grassy fields. It is a highly recognizable species and most populations exist in areas with high levels of human development (e.g., in valley bottoms and along lake, river, and marine shorelines).
Disturbance by human activities poses a significant threat to these species, especially during the breeding season. Because of the concentration of nests at one site, a single event can affect an entire population at one time. Untimely visits to colonies can allow predation of eggs or young by gulls and corvids, or chilling or overheating of eggs which reduces hatching success. Severe disturbances can result in complete reproductive failure.
In addition, habitats of colonial nesters are threatened by development, disturbance, and pollution. Wetlands near cities and towns continue to be drained for residential, industrial, or agricultural expansion. Other wetlands can be so heavily used for recreational purposes as to discourage use by these species. Stands of mature trees used for nesting by Great Blue Herons are often as attractive to loggers and developers as they are to herons.
The species in this manual are all at, or near, the top of the food chain, and can suffer from concentration of organochlorines and heavy metals, which may reduce reproductive success. All three grebes, especially the Western Grebe, and the Great Blue Heron are vulnerable to marine oil spills. Because of threats to their habitat, their vulnerability due to seasonal concentration, and their sensitivity to disturbance, American White Pelican and Western Grebe are listed on the British Columbia Red List as Endangered and Threatened, respectively, and Great Blue Heron is listed on the Blue List as Vulnerable (B.C. Wildlife Branch 1993).
The inventory and monitoring of these species is important because of the fragile nature of their habitat and populations. This inventory manual is one of many manuals being developed for all wildlife and plant taxa in British Columbia by the Resource Inventory Committee. These manuals are intended to provide standard methods for the collection of data on populations. The purpose of this manual is to provide protocols for inventory at three levels of survey intensity: presence/not detected (possible), relative abundance, and absolute abundance.
This section includes a brief overview of the biology and distribution of each member of the inventory group. This information is taken primarily from Campbell et al. (1990). Table 1 lists the location and size of major British Columbia colonies of each species. Also included in this section is a discussion of species-specific factors to consider when developing survey programs.
The Red-necked Grebe is a widely distributed and fairly common breeder in marshes and lakes in the interior of British Columbia. Breeding populations are highest in the Central Interior, Southern Interior, and Peace Lowland. In winter, it is widely and sparsely distributed along most of the coast and on open waters of the Southern Interior and Southern Interior Mountains. It is most abundant during migration and in winter in shallow bays and estuaries along the coast (Campbell et al. 1990).
Red-necked Grebes breed in shallow marshes or in areas of emergent vegetation along the edges of lakes. They are loosely colonial, with nests usually well spaced along the edges of emergent vegetation. Nests are soggy, floating platforms constructed of aquatic vegetation, and attached to stems of bulrush or cattail. Clutch sizes range from 3-6 eggs, but only 1 or 2 young are usually produced each year (Campbell et al. 1990).
2.2 Eared Grebe Podiceps nigricollis
The Eared Grebe is a widely distributed bird in the interior of British Columbia from spring through fall, with numerous, but discrete, breeding areas. Breeding populations are highest in the Central Interior and the Peace Lowland. Most Eared Grebes winter south of British Columbia, although a few remain in the south interior and along the southern coast, particularly in the Gulf Islands (American Ornithologists' Union 1983; Breault et al. 1988; Campbell et al. 1990).
Eared Grebes nest mainly in tight, compact colonies on sheltered freshwater marshes, lakes, ponds, and sewage lagoons. Nests are usually platforms placed in stands of bulrushes, sedges, cattails, and other emergent vegetation. Clutch sizes range from 3-8 eggs. Data on success rates are confounded by mixing of broods from different nests (Campbell et al. 1990).
The Western Grebe is widely distributed in the southern half of British Columbia. As a breeding bird, it is currently restricted to four colonies (Table 1). From fall through spring, concentrations of this species can be found on nearshore marine waters in the southern Strait of Georgia, and on large lakes in the southern interior. Western Grebes winter commonly on the south coast with concentrations at Boundary Bay, Burrard Inlet, Iona Island, Mill Bay, Saltspring Island, Deep Bay, Comox, and Campbell River. Very large concentrations occur in areas in March where Pacific Herring spawn (e.g., Barkley Sound, Nanoose Harbour, Qualicum Beach). Little is known of their migration routes (Campbell et al. 1990).
Western Grebes usually nest in stands of bulrushes or cattails, in water deeper than that used by Red-necked and Eared Grebes. Nests are soggy, floating platforms of aquatic vegetation and sticks. Clutch sizes range from 3-7 eggs. Most pairs probably raise two young (Campbell et al. 1990; Storer and Neuchterlein 1992).
The American White Pelican is a summer visitant in British Columbia. In this province, it is very local in distribution and breeds at only one site, Stum Lake about 25 km northeast of Alexis Creek. In summer, it forages over a wide area in the Chilcotin Plateau. Migration occurs mainly in a narrow interior corridor including parts of the Nicola and Okanagan valleys. Elsewhere in the province, it is only rarely recorded (Dunbar 1984; Campbell et al. 1990).
American White Pelicans nest on bare, rocky outcropping islands at Stum Lake. Nests are untidy mounds of dirt, sticks, reeds, and debris, or are mere depressions in sand or gravel. Most clutches contain 2 eggs and 1-2 young fledge. However, nest success is extremely variable (Dunbar 1984; Campbell et al. 1990).