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Sumner W. Matteson and William K. Volkert
A variety of sizes, shapes and habits
Transcontinental travelers | Stop-over habitat is critical en route
Choice places to see shorebirds in Wisconsin
Know your Wisconsin shorebirds (chart)
Every spring, the greatest long-distance migrants in the world – shorebirds – pass through Wisconsin on an extraordinary journey from as far away as southern South America to breeding grounds in arctic Canada, many flying 8,000 miles or more. This elegant group of birds, mostly comprised of sandpipers and plovers, frequents coastal and inland stopover sites – mud flats, marsh edges, flooded fields, ephemeral pools and the shores of lakes and lagoons – to refuel on invertebrates: insects, crustaceans, mollusks and worms.
Similar long-distance fall migrations occur every year as shorebirds retrace their journeys or fly south along the north Atlantic coast across to Surinam and down South America. Despite these remarkable flights, shorebirds are often little appreciated as they are less colorful than wood warblers and other songbirds, and not as prominent as hawks, owls and eagles. We encourage you to take a closer look.
A variety of sizes, shapes and habits
Foraging shorebirds have bills of varied shapes and sizes designed for feeding on invertebrates in upland and wetland habitats. Shorebirds are opportunistic and take the largest, easiest-to-catch invertebrates; some, such as the willet, greater and lesser yellowlegs, common snipe and the ruddy turnstone, consume a diet from insects to crabs. In the Apostle Islands, we have observed ruddy turnstones rolling herring gull eggs out of nests in attempts to break the shells, and ruddy turnstones are notorious predators of common tern eggs.
Marauders aside, shorebirds are delightful to watch; most pick or probe for food from mud flats, beaches, shallow waters and shorelines, but with noticeable differences that reflect variations in bill length and habitat. The American avocet uses its long, thin, upcurved bill to sweep side to side through shallow water and mud. Both yellowlegs typically pick and deeply probe after invertebrates in shallow water and chase minnows from time to time. Godwits use their long bills to probe mud flats and shallow pools. The constant bobbing of spotted sandpipers is a familiar sight as they dart hither and yon along shorelines for insect prey. And in mixed flocks of western and semipalmated sandpipers, the western's longer bill allows it to probe deeper water. In general, water depth and body size of foraging shorebirds correlate: larger birds forage in deeper water up to seven inches deep.
The casual observer may not even be aware of shorebirds since their earth-toned and light shaded plumage blends in well with the immediate surroundings of flooded farm fields, shorelines and mud flats. These excitable birds cannot be easily approached and are best seen through a high-powered scope or binoculars from a road edge, a dune or while standing along some far-flung beach accessible only by boat.
The sandpipers, along with phalaropes and closely related birds, comprise the largest family (Scolopacidae) of Wisconsin shorebirds (33 species). All totaled, 41 shorebird species have been recorded in the state during the past half-century; this includes five species (from another part of the country or from another continent) characterized as "accidentals" that arrive on the winds of a major storm system, and seven species that breed in the state. Shorebirds range in size from the least sandpiper – the smallest sandpiper in the world at only six inches in length and weighing scarcely more than a half ounce, to the marbled godwit, which stands 18 inches high and weighs about a pound.
Imagine one of these sandpipers – the white-rumped sandpiper – which weighs only one and a half ounces and measure about seven and a half inches long, flying every spring from Tierra del Fuego at the southern tip of South America to its tundra nesting grounds in the Arctic – a 9,000-mile journey! This diminutive bird flies high in the thin night air – as do most shorebirds – resting during the day at inland and coastal sites in Wisconsin and elsewhere across the continent. The best time to see white-rumps in Wisconsin is during the third week of May through the first week of June. In fall, the numbers are far fewer because they follow a different migration route – principally from Hudson Bay along the north Atlantic Coast south through the West Indies and northern South America, though some come through Wisconsin between mid-July and early October.
Then there is another renowned long-distance migrant – the sanderling its white two-ounce frame scurrying along the beach on distinctive black legs is common in late summer on our Great Lakes shores. This eight-inch bird flies every spring from coastal South America to breeding grounds in northeast Greenland, a peregrination exceeding 8,000 miles. (Sanderlings also nest in northern Alaska, across portions of northern Canada, and fairly close to the North Pole on Ellesmere Island.) Sanderlings migrate through Wisconsin from May 20-30 in spring and mid-August to early October in fall.
Not to be outdone, the lesser golden-plover flies from South America to nest in the High Arctic tundra and elsewhere in Canada and Alaska. This bird, abundant here in the mid-1800s, travels farther in a single flight than any other Wisconsin shorebird (except for the less common Hudsonian godwit), reportedly flying nonstop for 2,000 miles to the Gulf Coast before refueling. And the black-bellied plover, a circumpolar nester, migrates from the Arctic Circle to wintering grounds as far south as central Chile and northern Argentina. Look for the black-bellied from May 15-25 in southern Wisconsin and from May 21 to early June in the north; for the golden-plover, May 1-15, along the Lake Superior and Michigan coasts and in our southern and eastern counties. During fall, the latter half of September into early October is a peak period for both species.
The killdeer is the most common of our six plover species. It is a "short-distance" migrant that winters in the Gulf and South Atlantic states and nests here on gravel parking lots, grassy park areas, rural roadways and farm fields.
The plover family also includes the semipalmated plover, which breeds from northern Alaska and the High Arctic south into Canada and winters as far south as central Chile and Argentina (Patagonia). Then there's the rare, state-endangered piping plover, a Great Lakes beach and dune denizen that has nested in the state intermittently, with two Wisconsin nests observed on Lakes Superior and Michigan shores during 2001. No one knows for sure where our few piping plovers winter, but it is likely between the Georgia coast and the Texas Gulf Coast.
Stop-over habitat is critical en route
Since shorebirds often feed in temporarily flooded fields and in shallow wetlands (including so-called ephemeral wetlands), some of their stopover habitat has disappeared due to development and agricultural use. Significant conservation efforts are stemming large wetland losses, but ephemeral areas don't enjoy the same protection. Hence migrating shorebirds are under considerable pressure to find suitable sites to rest and refuel.
Shorebirds must arrive on Arctic breeding grounds in good physical condition to nest successfully during the brief Arctic summer. The body fat these birds accumulate during stopovers in Wisconsin and other midwestern states is critical for completing their long, arduous migration, as well as providing energy to produce viable eggs. As breeders, shorebirds exhibit a variety of mating strategies from monogamy to polygyny. Polyandry (females pairing with multiple males) and promiscuity are rampant among some species.
Estimating population sizes of long-distance migrants is difficult. Biologists rely on several methods, including surveys at annual staging sites, such as Delaware Bay on the East Coast, San Francisco Bay, and the Copper River delta in Alaska. Monitoring long-term population changes is a major objective of the United States Shorebird Conservation Plan. The plan aims to identify and maintain wintering, breeding and migration habitat, stabilize declining populations, maintain common species and restore shorebird populations in the Western Hemisphere through cooperative international efforts. To that end, a growing coalition of public and private groups have organized the Western Hemisphere Reserve Network to identify and protect important migration routes.
In Wisconsin, the Wisconsin Society for Ornithology works closely with the Department of Natural Resources on shorebird management. Contributions to WSO's Sam Robbins Shorebird Endowment Fund underwrite the costs of modifying water levels on three state wildlife areas to accommodate shorebirds: Theresa Marsh in Dodge County, Mead Wildlife Area in Marathon County and Crex Meadows in Burnett County.
Water drawdowns promote the growth of aquatic vegetation as waterfowl food and create mudflats during peak shorebird migration.
Habitat ranging from exposed mudflats to shallow water provide ideal conditions for a variety of species, from small shorebirds ("peeps") to large waders such as godwits, willets, dowitchers and yellowlegs. Drawdowns also attract a variety of unusual shorebirds that provide ideal viewing opportunities for birders.
During spring migration, shorebirds often congregate in shallow, receding wetlands where large numbers of midge larvae, particularly bloodworms, overwinter. Drawdowns mimic these conditions. Partial drawdowns, where at least 20 percent of the impoundment is less than eight inches deep are usually all that is needed to create food sources for invertebrates, which in turn attract shorebirds.
When semipermanent wetlands are managed for shorebirds, uplands surrounding the emergent vegetation are flooded in early spring, killing wet meadow plants and providing detritus for midges.
Since flooded fields and shallow water habitats change year to year depending on snowmelt and spring rainfall, management efforts are critical for sustaining shorebirds. By meeting their needs, we and future generations can guarantee that these masters of the wind will long visit us on their marvelous, transcontinental journeys.
Sumner W. Matteson is an avian ecologist with DNR's Bureau of Endangered Resources. William K. Volkert is a DNR naturalist and wildlife educator at Horicon Marsh.