THE WESTERN SANDPIPER

Anyone who visits the seashore in summer will sooner or later encounter sandpipers scurrying along the beach. In British Columbia, the two hottest spots for shorebirds are mudflats in Boundary Bay near Vancouver and Tofino Inlet near the town of Tofino. The most numerous species is the Western Sandpiper that migrates in the hundreds of thousands along our coast each spring to breeding grounds in western Alaska, and back again in summer for winter quarters in Central and South America. Over the past few years, a team of scientists and students have pieced together the remarkable migration of this bird (Condor 98:10-21; Wilson Bulletin 108:662-672; Auk 114:456-466).

In spring, the small sandpiper weighing about the same as six 'loonies', departs its winter quarters and travels hundreds or thousands of kilometers on a single flight. The 'airports' for this bird are San Francisco Bay, Grays Harbor, the Fraser River delta, Stikine River Delta, and Copper River delta.

But many bypass one or more 'airports' before stopping. One bird carrying a transmitter traveled 3200 kilometers from San Francisco to the Copper River delta in under 40 hours! How do they do it? The research indicates that they probably ride strong high elevation winds blowing from the south to carry them north in spring, and blowing from the north-west to carry them home in summer. And when they return south, we think they might fly non-stop from Alaska to southern BC by a direct flight across the Gulf of Alaska by riding westerly winds over the Pacific. These flights are remarkable feats of endurance that require a lot of fuel in the form of fat. Western Sandpipers carry about half their lean weight in fat for the journey.

And that is why mudflats are so important.

Microscopic, single-celled algae that live in the mud migrate in between sediment grains and lay down mucous trails similar to trails produced by snails which act to bind sediment grains together. The smooth surface of the mucous allow the incoming tidal waters to slip over the sediment instead of eroding it creating a stable environment for invertebrates to live in. This microalgae also forms a primary food source for mudflat food chain. Invertebrates, such as, worms and amphipods (tiny mud shrimp) feed on this biofilm material and are in turn fed on by shorebirds, such as sandpipers. On the east coast of Canada, in the Bay of Fundy this microalgae-amphipod-sandpiper relationship is very straight forward and well documented. However, on this coast the connection between what inhabits the mudflats and what the birds remove during their stopover has been very elusive.

Work by the Canadian Wildlife Service researchers Dr. Terri Sutherland, Dr. Bob Elner, Pippa Shepherd and Holly Butler found that the sandpipers fed in very soupy fine-grained sediment that contained gel-like mud properties loads of invertebrates. Harpreet Gill searched through the smallest size fraction of worms and found up to 9 worms per cubic centimeter. This is equivalent to about 300 worms per average chocolate brownie slice. Our preliminary experiments indicate that the shorebirds removed worms and tiny crustaceans. It is important that these groups of invertebrates maintain a population density during the 6 week stopover period of shorebirds on the local tidal flats.

back to Butler on Birds homepage