Hosts Many Migratory Shorebirds
(Published by The Quoddy Tides, July 13, 2001)
During late summer and fall, Cobscook Bay hosts one of nature's most amazing annual events. Many thousands of shorebirds migrating from summer breeding sites in the arctic and subarctic stop in the bay for up to several weeks, attracted by good food and rest to restore their weary bodies. At low tide, they scamper up and down the flats or probe deep into the mud to feed on abundant worms and other invertebrates. When the winds and other natural cues tell them the time is right, they fly on to wintering grounds in South America, often without another stop in between.
An observant birdwatcher may count fifteen to twenty species of shorebirds feeding in the mudflats throughout the migration season. Black bellied plover, sanderlings, semipalmated sandpiper, least sandpiper, greater and lesser yellowlegs, and shortbilled dowitchers are the more common shorebirds observed here. Less frequent visitors include white-rumped sandpipers, Baird's sandpipers, and red knots. Their behaviors are as interesting and diverse as their names.
Charles Duncan, in The Nature Conservancy's Wings of the Americas program, has special knowledge of these annual visitors to Cobscook's shores. While a resident of East Machias for 17 years, and professor at the University of Maine at Machias until 1999, he spent countless hours studying the habits of shorebirds.
"The short-billed dowitcher, which actually has a long bill, finds food by touching it with its bill as it probes up and down deep in the mud. It looks like a sewing machine as it feeds, which makes it easy to pick out from other species even without binoculars," says Duncan. "In contrast, the black bellied plovers are visual feeders - they have great big eyes - and never probe. You can see them running around looking for bloodworms at the edge of the water as the tide recedes, before the worms have time to burrow down. They see the food and then 'bam!'"
Concern over declining numbers of shorebirds has increased since the 1980's. Lindsay Tudor, a wildlife biologist for the Department of Inland Fisheries and Wildlife, is one of several biologists responsible for trekking across mudflats and saltmarshes with spotting scope in hand to count shorebirds in late summer and fall.
"We started surveys in 1989 and completed the most recent round in 1999. In Cobscook Bay, the Lubec flats and the flats on both sides of Eastport are still among the hot spots for shorebird activity in the fall," says Tudor. "In the late 1980's shorebirds shifted in migration so a lot of our birds are now staging in the top of the Bay of Fundy. No one really knows why, although a decline in the availability or the quality of feeding flats may be one reason shorebird numbers are down."
It is critical that the shorebirds build up enough fat to migrate. When the shorebirds leave Maine, many of them fly more than 1,500 miles over the ocean to South America without stopping.
"The semipalmated sandpiper crosses the ocean in a single flight lasting three days. This is all fueled by fat, and these birds eat like crazy. At a stopover like Cobscook Bay, they need to double their body weight to make this flight," explains Duncan.
Shorebirds need to feed uninterrupted to build up their fat reserves. As Duncan reports, even innocent human activities, like walking a dog along shore, can be devastating to these birds.
"Bird watching is great, and should be encouraged. A person standing relatively still with binoculars or a scope is a minor disturbance, but any activity that forces birds to fly means less time for them to feed," Duncan says.
Whether or not the birds have built up enough fat, they will respond to the movement of the wind and temperature changes, along with other natural cues, to continue their flight south. If underfed, they may die mid-flight or be too weak to survive after reaching their wintering grounds. Places for rest are also important to their survival.
Tudor reports, "Some of their roosting sites in the Cobscook area have been disturbed. For example, one roosting site is now used as a parking area, and the birds are rarely seen in those flats anymore."
She adds, "For some reason, they aren't bothered by clammers. If you act like a clammer, bending down, walking slowly, birds don't seem to mind."
Shorebirds face threats to their survival throughout the year. In their arctic or subarctic breeding grounds, some habitat is being altered by a population explosion of snow geese. As they fly south and stop at staging areas in Maine and other parts of the Northeast coast, disturbance from beachgoers, pets, 4-wheel drive vehicles, or other human activities keeps them away from their feeding and resting areas. Development along parts of the coast has wiped out habitat they need to survive migration. Pesticide use and hunting in South America impacts their survival during the winter.
When they fly north in the spring, many shorebirds stop in Delaware Bay to eat horseshoe crab eggs. However, an increase in horseshoe crab harvesting as bait for the eel and conchshell fishery has caused a huge drop in the abundance of eggs. Without enough food, the birds are unable to complete their northward migration or arrive in such poor condition that they lay fewer eggs or none at all.
With such a complicated life history, migratory shorebirds require management that relies on cooperation between countries and different partners throughout the United States. Areas protected by landowners and the Department of Inland Fisheries and Wildlife in Cobscook Bay are among the most significant wintering and staging areas for shorebirds in the state. Horan Head, Tide Mill Farm, the South Lubec Sand Bar, and Commissary Point are good areas for shorebird viewing during migration season.
This column was prepared by Cheryl Daigle. Cobscook Soundings was a monthly column produced by the Maine Chapter of The Nature Conservancy. Its purpose was to share what is known about the workings of the Cobscook Bay marine environment, so that all who make decisions about the use or care of the bay have the best available information.
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