Comox Valley Naturalists Society
Knowing Nature . . .
Summer on the Wane
August 26, 2005
The shorebirds are migrating south, a sure sign that summer is on the wane. Our estuaries and mudflats are teaming with birds, wading and scuttling along the shores. Their bills go up and down like a sewing machine, probing mudflats rich with tiny worms and snails.
When a Peregrine Falcon enters the scene, the birds fly up en masse. As the flock wheels overhead their synchronized motions are perfect. There is a flash of white under wings as the group pivots in unison. When the danger has passed the flock gracefully lands and the busy feeding resumes.
On closer inspection, some of the birds are small, with short bills, and others are larger with longer bills. Some are pale, some are dark. Some bills turn up, and some curve down. Some chatter, and others have a single note. Nicknamed “peeps” or “waders”, the bird species that inhabit the edges of our oceans and wetlands are collectively called shorebirds.
Shorebirds can be distinguished from other birds by their upright posture, narrow bills, long legs (some more so than others) and pointed wings. Some are boldly patterned, but many are finely mottled with brown, gray, rust, white or tan. Most shorebirds travel together in flocks, and prefer open habitats.
Shorebirds have a reputation for being some of the best fliers around. They aren’t the fastest, but can fly Olympian distances, migrating thousands of kilometers without a rest. A transmitter on a Western Sandpiper revealed that it flew 3200 km, from San Francisco to Alaska non-stop. A Pacific Golden Plover, wintering in Hawaii, traversed 4500km non-stop across the ocean to Alaska. Shorebirds can reach cruising speeds of up to 100 km/hour. These remarkable fliers know how to ride air currents, which undoubtedly helps speed their journey. Despite amazing feats of speed and endurance, many birds succumb to poor weather or starvation. Conditions have to be right to make the flight!
Traveling is the lifestyle of a shorebird, and it is necessary for survival. Migration starts in the spring, when shorebirds migrate north, leaving winter feeding grounds in tropical regions such as Central and South America. Along the way, flocks periodically touch down to fuel up where food is abundant. Birds that migrate along the Pacific coast, known as the Pacific Flyway, stop at food-rich river deltas, estuaries and bays.
The major stopover sites are called staging areas. At staging areas, large concentrations of birds gather for feeding, including up to 80% of the members of some species. A major staging area in BC is Boundary Bay, near the Fraser River delta. Population concentrations at staging areas make shorebirds vulnerable to oil spills and pollutants. Several staging grounds have been lost, or reduced, by human development. Shorebirds are declining worldwide as a direct result of human activity. Hopefully, action to protect staging areas and shorelines will slow this trend.
Northbound migrating birds journey to the Arctic to breed. In the northern lands there are fewer predators, and the long hours of daylight are suitable for rearing young. Most shorebirds species nest on the ground in open, grassy tundra. At this time, shorebirds are in breeding plumage, and feather colours and patterns are at their finest.
Several shorebird species form monogamous pairs, but some have an uncommon mating system known as polyandry. In this system, the female may mate with several males. After the female lays a clutch or eggs, she then abandons the nest, leaving one or more males in charge of bringing up young. The female then goes on to find a new mate, repeating the cycle over again. In some polyandrous species, such as Phalaropes, the females are larger and more colourful than males.
As soon as nesting is finished, many shorebird species begin moulting into non-breeding plumage. Non-breeding (also called winter) plumage tends to be duller than breeding plumage. Changes in plumage cause some species to look markedly different, causing much confusion amongst bird watchers. By summer, shorebirds begin to migrate south. Migrants pass our shores through the summer months, peaking in September.
Shorebirds are an important part of shoreline ecosystems. In a mudflat, there are microscopic algae mixed with grains of mud. Invertebrates, such as worms, snails and tiny shrimp, feed on the algae. The invertebrates form the main diet of the mud-probing shorebirds. The bird droppings, or guano, fertilize phytoplankton. Fish feed on phytoplankton, and we eat the fish! In making the connections in the food chain, we begin to realize the importance of birds like shorebirds.
Shorebird watching is best on an incoming tide. Good spots for viewing include the Courtenay and Campbell River estuaries, and Oyster Bay Shoreline Park (south of Willow Point). During migration, please keep dogs on a leash along our shorelines. When disturbed by chasing dogs, shorebirds can’t rest and fuel up on the food they need to sustain them on long flights.
Photographs for this article are courtesy of Mike Yip. Mr.Yip is an avid photographer and bird enthusiast. His new book, Birds of Vancouver Island, illustrated with colour photographs, is available at Graham’s Jewelers in Courtenay and Blue Heron Books in Comox. Additional images can also been viewed on Yip’s web site Vancouver Island Birds.
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