Ian Robertson

Robertson Environmental Services Ltd., 1525 – 200th Street, Langley, B.C. V2Z 1W5

Abstract: Systematic aerial surveys for aquatic birds were conducted in February 1996 and August 1999 with supplemental ground surveys in 1999 to determine species composition, habitat use, and the potential role of river regulation on use patterns following changes in flow of the Peace River by the W. A. C. Bennett Dam since 1967.

Winter surveys indicated that open water, restricted to the river mainstem, attracted a small population of water-associated birds and raptors. Approximately 84% of the 366 birds observed were Common Mergansers, 45% of which were concentrated within 3 km. of the dam. Nineteen (63%) of the 3 1 Bald Eagles recorded in this survey were also recorded here.

The late August surveys coincided with the late breeding season of most of the river-using species expected in this area, the waterfowl moulting period, and the early and middle phases of post-breeding dispersal and fall migration. Twenty-six species were recorded, 20 of water birds and six of raptors. Of the total of 3,482 individuals recorded during aerial surveys, 5 1% were Canada Geese (905) and Mallards (885). Gulls comprised 24% and other fairly common species were Green-winged Teal (240) and Spotted Sandpipers (154). Bald Eagles (25) were by far the most common raptors observed. While birds were distributed along the entire length of the river, 60% of the birds were observed between Cache Creek and the Pine River (27% of the linear area). The major concentrations of geese, dabbling ducks and gulls in this area may have been influenced by the proximity of Fort St. John and food sources associated with its garbage dump, sewage lagoons, agriculture, and grain processing industry. While most species occurred in greatest numbers in non-mainstem (oxbow, back channel) habitats, certain numerous species (Canada Geese, gull sp.) and characteristic riverine species (Common Merganser, Spotted Sandpiper) were found predominantly in or beside the river mainstem.

Open water conditions provide increased winter habitat for Common Mergansers, their winter numbers being seven times that of late summer. Regular water level fluctuations, though small, appear to have a greater potential effect on non-mainstem compared to mainstem habitats. These quiescent, unscoured backchannel habitats, internally regulated in many areas by beaver dams, provide in the short term a productive and stable environment for waterfowl.

Key words: Bald Eagle, Common Merganser, dam effects, Haliaeetus leucocephalus, Mergus merganser, Peace River, waterfowl

Robertson, I. 1999. Surveys of water-associated birds on the Peace River downstream of the W.A.C. Bennett Dam. British Columbia Birds 9:3-10.