Tuesday, April 20, 2010

SHOREBIRDS ON THE MOVE


Every spring, about the beginning of April, flocks of shorebirds begin their annual migration up the Pacific coast on their way to Alaska and other points north. Sandpipers and plovers by the tens of thousands use the coastline as a pathway to their summer homes, feeding on the abundant populations of marine invertebrates and depositing fat to fuel their long-distance flights to their breeding grounds. Some birds leave the Washington coast and fly directly across the Gulf of Alaska to southern Alaska, where they stop at estuaries such as the Copper River Delta.



The most common species are Western Sandpipers, Dunlins, and Short-billed Dowitchers, in that order. At the same beaches, mudflats, and tidal pools are smaller but still substantial numbers of Black-bellied and Semipalmated Plovers, Greater Yellowlegs, Whimbrels, Marbled Godwits, Ruddy Turnstones, Red Knots, Sanderlings, Least Sandpipers, and Long-billed Dowitchers. At the same time, Black Turnstones, Surfbirds, and Wandering Tattlers feed along rocky shores as they move north, and Red-necked and Red Phalarope flocks settle on the ocean offshore.

These birds take advantage of a spring flush of invertebrate growth and recruitment, and they find no lack of goodies to help them put on weight. Amphipod crustaceans, polychaete worms, and small bivalves are among the most abundant fauna in birds that feed on and in sand and mud. These animals are so abundant that just about all the shorebird species using the area feed on them. Barnacles, mussels, and snails are staples of the rock shorebirds, and planktonic crustaceans fill the bellies of phalaropes.

Shorebird migration peaks on the Washington coast in the last week of April and first week of May, when the maximum number of species and individuals are present. Grays Harbor and Willapa Bay and the beaches adjacent to them always support the largest numbers, and the abundance of these birds provides a stirring spectacle every spring. Concentrations of some species in Grays Harbor are the highest south of Alaska.

And there is a Grays Harbor Shorebird Festival every spring to enjoy these concentrations: http://www.shorebirdfestival.com/.

Unfortunately, shorebird numbers have been declining, so the spectacle gets a little less spectacular every year. More importantly, we don’t have a good handle on the cause of the decline. Presumably it relates to loss of habitat on either the wintering grounds or at migration stopovers, as the arctic and subarctic breeding habitats are still relatively intact.

It’s also possible that anthropogenic changes are reducing the abundance of shorebird prey, another factor that we don’t know much about on a grand scale. There are still lots of shorebirds, so we have some time to work out an effective conservation plan, and there is such a plan for the U.S. (http://www.fws.gov/shorebirdplan/).

Dennis Paulson

2 comments:

Matt said...

You should've mentioned the Shorebird Festival at Gray's Harbor next week. http://www.shorebirdfestival.com/

Slater Museum of Natural History said...

Thanks, Matt. I did so, with only a week to spare.

Dennis