A fresh analysis of two decades of daily counts at one of three extensive intertidal flats in the Fraser River Delta, in British Columbia, has underscored the area’s critical importance to shorebirds that migrate every year along the Pacific Flyway.
According to researchers from Environment Canada and Bird Studies Canada, 600,000 Western Sandpipers and 200,000-250,000 Dunlins typically foraged and roosted at the flat, known as Brunswick Point, every spring between 1991 and 2013.
The estimates represent 14-21 percent of the total flyway population of Western Sandpiper (estimated to be 3.5 million) and 30-50 percent of the flyway population of Dunlin (550,000), and in some years, the percentage may have been higher.
Once uncertainties about length of stay and random variation are figured in, say Mark C. Drever, Moira J. F. Lemon, Robert W. Butler, and Rhonda L. Millikin, the median number of Western Sandpipers in 1994 may have been 1.8 million, or 42-64 percent of the total Pacific Flyway population.
What’s more, the researchers write that aerial surveys indicate the birds counted at Brunswick Point represent only about 40 percent of all the sandpipers that stop in the estuary each spring. Many thousands more Western Sandpipers and Dunlins, they say, use the two other intertidal flats, Sturgeon Banks and Boundary Bay (Hotspot Near You No. 173).
“Thus, it is possible that entire Flyway populations of both species may be found on the Fraser River Delta during migration, underscoring the overall importance of the entire estuary.”
Effective conservation measures for Western Sandpiper and Dunlin, conclude Drever and his colleagues, should focus on protecting the mudflats as feeding and roosting sites, and securing the sites from disturbance and pollution.
The Fraser River Delta was designated a site of hemispheric importance in the Western Hemisphere Shorebird Reserve Network in 2005.
Read the paper
Mark C. Drever, Moira J. F. Lemon, Robert W. Butler, and Rhonda L. Millikin, 2014, Monitoring Populations of Western Sandpipers and Pacific Dunlins during Northward Migration on the Fraser River Delta, British Columbia, 1991–2013, Journal of Field Ornithology 85 (1): 10–22 (PDF).
A version of this article appears in the June 2014 issue of BirdWatching. Subscribe.