A huge wave of birds is moving through the Lower Mainland, as the annual spring migration progresses up the coast. Hundreds of thousands of birds make their way north in April and May, heading for northern latitudes where they nest and rear young in the long daylight hours. Skeins of snow geese head to Wrangel Island off the coast of Russia, while Pacific black brant fly from Baja California to the high Arctic. Small groups of songbirds appear fleetingly in trees and bushes overnight, feed hectically for a few hours or days, and then move on. Mountain bluebirds pause to feed on caterpillars in a seaside park; bright-coloured warblers flit through the tree tops; white-crowned sparrows suddenly sing from a city cherry tree.

Dense flocks of sandpipers and other shorebirds make extremely long journeys, traveling from as far away as Suriname, Peru, and Ecuador on their way to Alaskan nesting grounds. On this 11,000 kilometre journey, they make relatively few stops, choosing estuaries and coastal bays with extensive tidal mud flats where they feed and rest. These hot spots include Grays Harbor in Washington, the Copper River delta in Alaska, and, in between, a key Canadian stopover: the Fraser River estuary. Many different shorebirds use the estuary, including dunlin, some of which also winter here, dowitchers, plovers, yellowlegs, sanderling and the tiny western sandpiper. That little “peep”, as birdwatchers affectionately call it, is only 17 centimetres long and weighs less than a granola bar. It averages 200 kilometres per day on its spring migration, but has been known to clock 3,000 kilometres in less than 48 hours. While many shorebirds use their long bills to probe in the mud for crustaceans and worms, western sandpipers employ a more unusual feeding strategy: they graze on diatoms and bacteria on the surface mud by sucking them up with the help of hairy tongues. Researchers have dubbed this interesting herbivorous behaviour as “snot feeding”, since the diatoms occur as a mucus-like scum on the mud.

The feeding strategy was discovered by local biologists studying the once abundant western sandpiper flocks. Up to 1.2 million sandpipers have been recorded on Roberts Bank and Boundary Bay during spring migration, yet in the mid 1990s, the numbers dropped dramatically, and the Canadian Wildlife Service and local universities struggled to discover what had happened. This is not a simple problem. Each migrating western sandpiper typically stays to feed for one to three days en route for the north, but this may vary depending on the state of the wind, weather and tides, the presence of predators, such as peregrine falcons, or other causes of disturbance, and the availability of suitable food and habitat. Some scientists consider the rebound of peregrine populations to have had a significant impact on sandpiper movements, and attribute the reduced numbers of birds to a function of the shorter period of time they are present to be counted.

However, habitat loss and increased disturbance of critical feeding areas is also cause for concern, and may prevent sandpipers from eating enough “fuel” for the journey. If they do not fatten up, they are in no shape to make the long trip and breed successfully. For example, at Roberts Bank, where “snot feeding” is particularly important, port expansion has been extensive in the last two decades. Increased marine traffic means more potential for pollution and spills, and night lighting, noise, and overhead power lines create hazards for wildlife. Delta farmlands that are extensively used by wintering and migrating shorebirds, such as dunlin and snipe, are increasingly built over for non-agricultural uses. Recreational disturbances at local beaches are frequent.

Shorebird populations have declined around the world and it is difficult to pinpoint causes. The Copper River International Migratory Shorebird Initiative is a fresh attempt to look at shorebird survival along the whole length of the Pacific Flyway, from South America to the Arctic. It will build on existing efforts by government and university researchers and regional organizations, such as the Pacific Flyway Shorebird Survey in California and the B.C. branch of Bird Studies Canada, both of which involve amateur enthusiasts.

Watching an actively feeding flock of small sandpipers working the mud flats as the tide recedes, knowing that they have flown thousands of kilometres and have many more to go before they can nest and rear young, is a remarkably fine way to spend a spring morning. I recommend you head to the beach; Boundary Bay, Roberts Bank, and Iona Beach Regional Park are all great spots (check the tide tables to arrive shortly before or after high tide). Happy birdwatching!

Anne Murray is a naturalist and the author of two books on Lower Mainland nature and ecological history—Tracing Our Past: A Heritage Guide to Boundary Bay and A Nature Guide to Boundary Bay.