LIVING on the EDGE
declining and shorebirds in trouble,
By Don Stap
with illustrations by
David Allen Sibley
On a sunny day in early August, a restless flock of semipalmated sandpipers rises from the shore of the Bay of Fundy and sweeps out over the water. Twisting and turning as one, rippling like a pointillist's flag, the tiny birds, which seemed so delicate a moment ago, charge through the air like raw energy. How, one wonders, can a diminutive body of such elegant curves and dainty features--glass figurines come to mind--contain such horsepower?
High energy and a sleek body built for speed are essential for shorebirds, among the greatest long-distance migrants in the avian world. Of the 49 species of shorebirds that breed in North America--plovers, sandpipers, godwits, yellowlegs, dowitchers, willet, avocets, stilts, and their allies--40 migrate from the Arctic or subarctic to Central or South America. Most of them fly more than 7,000 miles round-trip, and many exceed 14,000 miles. Nonstop flights of several days, at average speeds of 40 miles an hour, are common. For the smallest shorebirds (you could mail a semipalmated sandpiper cross-country for 34 cents), such journeys are nearly unbelievable.
When the flock of semipalmated sandpipers settles down again on the rocky shoreline, Peter Hicklin, a biologist with the Canadian Wildlife Service, estimates that there are 8,000 of them. Yesterday there were twice as many, he tells me, and only three days ago there were 200,000. In some years as many as 1.4 million semipalmated sandpipers, possibly 95 percent of their world population, stop here, where the planet's greatest tides--they rise and fall as much as 50 feet--expose miles of food-rich mudflats. Here the sandpipers feed furiously, adding fat reserves for the journey ahead, doubling their weight within two weeks. Then, when the time is right, they rise into the sky, head out over the ocean, and are not seen again in these latitudes until the days have grown long once more and the snows are melting on the Arctic tundra.
Since time immemorial, migrating shorebirds have depended on stopover sites such as the Bay of Fundy and Delaware Bay. This dependence has only increased as wetlands throughout the continent have been destroyed. Of the estimated 215 million acres of wetlands that once existed in the contiguous 48 United States, only 103 million remain today. In 1986 a coalition of concerned organizations--including the Manomet Center for Conservation Sciences, the National Audubon Society, Philadelphia's Academy of Natural Sciences, and the World Wildlife Fund--established the Western Hemisphere Shorebird Reserve Network (WHSRN) to promote the importance of protecting critical stopover sites. "We need to think in terms of the hemispheric importance of such areas," says Jim Corven, director of the WHSRN. With that in mind, the group has identified 300 important stopover areas, from Alaska to Tierra del Fuego. Besides the Bay of Fundy, eight sites in the United States--the Copper River delta, in Alaska; Washington's Grays Harbor; the Great Salt Lake; San Francisco Bay; the Lahontan Valley, in Nevada; Cheyenne Bottoms, in Kansas; Delaware Bay; and the Yukon River delta, in Alaska--have also been designated as "areas of hemispheric importance" because they are host to either more than 500,000 shorebirds or 30 percent of a flyway's population.
As with so many similar efforts, this one comes none too soon. The spectacle of hundreds of thousands of birds in one place at one time belies what 25 years of surveys have revealed: Shorebird populations are declining, drastically for some species. Brian Harrington, a shorebird expert at Manomet and the director of the International Shorebird Survey, recently analyzed the data from more than 50,000 censuses in the eastern and central United States. Of the 26 species he focused on, 5 had declined more than 25 percent, and 16 others had declined between 5 percent and 20 percent. Other studies suggest that from 1974 to 1983, some shorebird species along the Atlantic coast declined as much as 80 percent.
Twenty-three years ago, when Hicklin first began studying semipalmated sandpipers, no one knew exactly why they congregated in such great numbers each August at the Bay of Fundy or where they went when they left. Since then, Hicklin has banded more than 32,000 birds, spent more days than he cares to remember sitting in a lawn chair in the middle of the mudflats observing foraging sandpipers, and sifted buckets full of Fundy mud to study its composition. Hicklin discovered that each day as the tides receded and the sandpipers began foraging, small shrimplike invertebrates known as Corophium volutator emerged from their burrows in the mud to look for mating opportunities. Each fall, the Corophium population peaked--with an average of 5,000 of the creatures per square meter--about the time the birds arrived, providing them with an abundant food source when they needed it most. As Hicklin told me the story of the Corophium and the semipalmated sandpipers, I was reminded of the similar, much-reported scenario at Delaware Bay, where horseshoe crabs jam the beaches each spring to lay their eggs (a fat-rich shorebird delicacy) just as migrating red knots arrive to rest and refuel. (See "The Removable Feast," May-June 2001.)
But semipalmated sandpipers are one of the species that appear to be in trouble. Hicklin worries about the effects of dams that were constructed in the 1950s and 1960s on many of the tidal rivers that empty into the Bay of Fundy, largely to "reclaim" land for agriculture. In 1993 he took two graduate students onto the mudflats where he had done his initial research 15 years earlier, to show them the abundant Corophium. "I walked onto the mudflats, and it was like walking in a different country," Hicklin says. "The mud was soupy. And there were no Corophium. I was in a state of shock." When Hicklin analyzed the mud, he found that the water content had doubled. Corophium need mud of a particular consistency, or the burrows they build will collapse. Now here, in a place where there had been tens of thousands of Corophium, there were none. Hicklin wonders if the effect of the dams is just showing up today. "The Bay of Fundy is a highly dynamic system," he says. "We don't understand it yet."
Any disturbance of the delicate balance between shorebirds and the environment in the Bay of Fundy will have a ripple effect that will eventually reach the shores of South America. Recently, at a conference Hicklin attended, he was greeted warmly by a complete stranger, who introduced himself and shook Hicklin's hand. Hicklin was confused until the man, a biologist named Eric Hansen from French Guiana, another important stopover site for the semipalmated sandpipers, smiled broadly and said, "Monsieur, I catch your birds." Hicklin was delighted to know that birds he had been banding were showing up in mist nets on the shores of French Guiana. "That's why we do this," he says. "The birds connect us."
I wondered if some of Hicklin's semipalmated sandpipers, blown off course, were among the peeps I have spent so many hours watching each fall and winter on the mudflats of the Merritt Island National Wildlife Refuge, a mosaic of marshes, sandy uplands, and brackish lagoons adjacent to Florida's Kennedy Space Center. There, in an effort to control outbreaks of salt-marsh mosquitoes--a square yard of marsh in prime mosquito nursery conditions can produce a million mosquitoes a day--the marshes have been impounded: 69,000 acres in all, divided into 76 jigsaw-puzzle pieces of marsh with moats of land surrounding them. This leaves the U.S. Fish and Wildlife Service with the unenviable task of trying to manage an altered ecology.
For shorebirds, water level is everything. (Four inches of water or less is the ideal for 70 percent of shorebirds.) From my vantage point--on a good day this means crouched in the cordgrass a short distance from a mudflat--the question of water level is simple: The plovers and the small sandpipers work the shallowest shards of water; just beyond them, in three to six inches of water, a few yellowlegs will be running to and fro, as if confused. In the deeper water beyond them, as deep as 10 inches or so, will be avocets and stilts. For Gary Popotnik, a wildlife biologist at Merritt Island, it's not so simple. "I spent half this week looking at the water levels in the impoundments," he says. "You're always out looking for which areas need attention, and that varies from year to year and day to day."
Drawing down the water in parts of the refuge for shorebirds as they arrive in the spring and the fall is complicated, in part because the tools are so basic--a few boards across the opening of the culvert that connects one impoundment with another. Popotnik's decisions often amount to this: Remove a two-inch board or a four-inch board. But what he has to keep in mind requires a chess master's grasp of possibilities and strategies, and a diviner's touch.
A gradual drawdown takes weeks. If the water drains too quickly, the mud will dry up so fast that the invertebrates in it--the shorebirds' food source--will die. Evaporation (always a possibility in Florida) can speed up the process; rainfall can reverse it. And overnight a good wind can drive water through the culverts from one impoundment to another, or blow it from the surrounding lagoons into the impoundments, not only raising the level of the water but increasing its salinity as well.
Popotnik must also be concerned with how water levels affect the vegetation. Draining the water from an impoundment will give seeds trapped in the mud an opportunity to germinate, and aquatic plants provide good habitat for the larval stages of the invertebrates that many shorebirds feed on. But if the mosquito-control district had its way, all the impoundments would contain at least a few inches of water year-round, since the salt-marsh mosquito lays its eggs in the mud. No mud, no mosquitoes. Moreover, the needs of shorebirds must be balanced with the needs of ducks, wading birds, and fish. So Popotnik watches the water. So do local fishermen, who, if they feel they need deeper water for their favorite spot, can destroy six months of work by lifting a board out of place and tossing it in the weeds.
The refuge has begun working on a system to lock the boards in place. More important, in 1995 Merritt Island launched a long-term project that, to date, has added 250 water-control structures to the original 100 gates to allow the more precise management of water levels. In addition, the impoundments in several areas have been opened to allow the free flow of water between the lagoons and the marsh. The effects of all this will be established in part by a year-round bird census that Popotnik has instituted, the first such comprehensive population monitoring carried out at the refuge. Volunteers and biologists conduct censuses three times a month, all year long. "In a few years we should be able to look at the data and see what's happening with shorebird populations," Popotnik says.
In the West, no stopover site is more important to shorebirds than the Great Salt Lake: 1,500 square miles of water with 400,000 acres of wetlands along the shores. Each July migrating Wilson's phalaropes descend on this oasis in the middle of the arid Great Basin by the tens of thousands, sometimes reaching concentrations as great as 600,000. A month later the local American avocet population may peak at 250,000 birds. The entire Pacific Flyway population of marbled godwits depends on the Salt Lake's bordering wetlands, the only known inland stopover site for this population of the species. On the northeastern arm of the lake, where the Bear River empties fresh water into the saline lake, lies the 74,000-acre Bear River Migratory Bird Refuge. Forty-seven miles of dikes impound the refuge's water, which is controlled in much the same way as at Merritt Island. "We used to keep the water deep all the time for waterfowl," says Vickie Hirschboeck, senior wildlife biologist at the refuge. "But now we want to provide shallow water, and lots of it, for shorebirds when they need it."
The refuge gets less than 15 inches of rainfall annually, and most of the water it receives arrives by way of the Bear River, which has had its water rights parceled out since the turn of the century. Upstream, Scottish Power, the region's electric utility, operates a hydroelectric dam, and water is diverted for irrigation by farmers in Utah and Idaho along the river's winding, 500-mile course. By law the national wildlife refuge is allowed as much as 2,000 acre-feet of water per day. "That's fine," says Al Trout, refuge manager, "but the amount of water flowing can vary from 6,000 acre-feet to 100 acre-feet, depending on the season. If the power company is using water to generate electricity, the water flow in the river is increased. But when the water is shut off to the generators, the flow fluctuates." Irrigation needs vary dramatically as well. If it rains in Idaho, the farmers stop diverting river water for irrigation, and the flow into the wetlands increases. The result is that peeps standing in an inch of water one day have water over their heads before long if the refuge doesn't figure out what to do with the excess water.
Midway across the country, in Kansas, is a 41,000-acre natural basin known as Cheyenne Bottoms. It is so attractive to shorebirds that the Western Hemisphere Shorebird Reserve Network estimates that each spring as many as 45 percent of all shorebirds migrating through the interior of the United States stop there on their way north. Hundreds of thousands of them--particularly dowitchers; Wilson's phalaropes; and white-rumped, Baird's, stilt, and semipalmated sandpipers--cram into the bowl-shaped wetlands. During the mid- to late 1990s, however, fewer and fewer birds appeared to be stopping at Cheyenne Bottoms. "It's hard to know for sure, though, because you can't count birds you can't see," says Helen Hands, a wildlife biologist for the Kansas Department of Wildlife and Parks. The problem, as Hands pointed out when she gave me a tour of the area, is cattails, dense stands of them, which spread acre after acre in the shallow water of the impoundments.
For eons, water levels at Cheyenne Bottoms fluctuated naturally, the area drying out some years, flooding other years--a cycle inhospitable to cattails. But in this century much of the water that would have flowed into the bowl-shaped depression has been diverted for agriculture. In the 1960s area farmers also began drilling more wells, further lowering the water table. Water shortages at Cheyenne Bottoms continued, which, with other factors, produced conditions that allowed cattails to invade the area in the 1970s.
In April 1989 Cheyenne Bottoms dried out completely. Overnight, tens of thousands of shorebirds that had been clustered around the last pools of water disappeared. Then, a few years later, the area began to receive above-average rainfall, and from 1992 to 1999 the problem was too much water. Cheyenne Bottoms has no natural outlet, so evaporation is the only way water levels fall. But with several years of heavy rains, that was not enough. The water remained until the fall of 2000.
Each year, the cattails claimed more acreage, clotting the open water that shorebirds prefer. And drawing down water or flooding areas with shallow water can be counterproductive in the long run, since at some times of the year this provides ideal conditions for cattails to spread. It's a perfect example of the kind of unpredictable ill effects that can result from disrupting the natural ecology. "There's just no easy answer," Hands says. It wasn't until drier weather arrived, after I visited Hands, that the refuge was able to send someone in to disk up the cattails.
"We assume that when a place like Cheyenne Bottoms isn't having a good year for shorebirds, those birds using the central United States during migration find other places, but we really don't know," says Manomet's Brian Harrington. "The problem is that there are far fewer wetlands than there used to be." The importance of managing these critical stopover sites wisely cannot be overstated. Hundreds of thousands of shorebirds funneling into a relatively small area puts great pressure on the resources. Shorebirds live on the edge as it is--of seasons, bodies of water, receding tides. They arrive on our shores when the air is filled with change and then, when our backs are turned, disappear. But not for long, we hope.
Don Stap, author of A Parrot Without a Name, teaches creative writing at the University of Central Florida. He is at work on a book about birdsong, to be published by Scribner.