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Diurnal Avian Corridor Maps
Identify river and forest systems that are valuable diurnal avian migration corridors.
To determine which river and forest systems act as valuable diurnal migration corridors the following methodology was employed. All river and forest systems with a north-south orientation or northwest-southeast orientation were included in the analysis. East-west rivers were not included in this analysis unless expert opinion or the Important Bird Areas (IBAs) mapping effort pointed out known sites as corridors for at least one group of birds (i.e shorebirds, raptors, etc.). These rivers tend to act more as stopover habitat for most species of landbirds and sometimes for waterfowl and shorebirds rather than as corridors since they are not oriented in the direction of spring or fall migration. Simultaneously, the state’s IBAs associated with a river system were mapped out and tallied. The IBA selection process is based on a combination of existing scientific studies, existing observational data, and the opinion of a panel of experts who determine whether a site is to be included as an IBA.
Corridors with existing IBAs were included if the selection criteria pointed to the value of an IBA as a migration corridor for various species and species groups. The remaining rivers were then analyzed using Google Earth for the presence of significant forest patches or continuous gallery forest along its shores. Selected river corridors required a minimum of 50% forest cover or gallery forest along at least one bank along a stretch of riverine corridor for inclusion. In some cases, portions of the corridor did not meet these criteria and were eliminated from further consideration. In a few instances in heavily agricultural landscapes, large blocks of forest habitat were patchily distributed along the shores, but were likely visible to migrating forest birds from one patch to the next and were included. In other instances, substantial wetlands along a corridor indicated a potentially valuable corridor for shorebirds or marshbirds. There was no attempt to thoroughly analyze waterfowl movement patterns in the state other than to include waterfowl as a potential component in the sites identified for landbirds, waterbirds, raptors, and shorebirds. Such an analysis would be a major undertaking requiring a large effort to radio tag or satellite collar hundreds of birds and dozens of species.
“Dominant bird groups / species”
This categorization is intended to be a general guide gleaned from IBA selection criteria and state expert opinion as to which groups of birds or bird species are most important in a selected river corridor and might be vulnerable to collisions with locally-sited communication towers, bridges, wind turbines, tall buildings, or other similar structures. This is not intended to be a comprehensive vulnerability assessment for a corridor’s avifauna, but serves only as a potential early warning system for biologists and developers. Developers should complete thorough pre-construction avian surveys for various projects sited in or along these corridors, paying special attention to those avian groups for which a river corridor provides known important habitat and passageway. Corridors noted with a double asterisk (**) are the only corridors where bridge construction projects are likely to be a serious issue with migrant birds due to the large river width, broad migration corridor, likelihood of foggy conditions on a regular basis, and potential height of any bridge constructed which may prove to be a hazard for migrant and resident birds.
**Lake Michigan shoreline
(east side of Door County from Rock Island south to Illinois state line)
Likely the most important migratory corridor in the state for 200+ species of migratory birds. Eight individual IBAs are located along the shoreline, namely (from north to south): Mink River Estuary-Newport State Park IBA, Toft Point-Ridges Sanctuary-Mud Lake IBA, Whitefish Dunes-Shivering Sands IBA, Point Beach State Forest IBA, Woodland Dunes Nature Center IBA, Cleveland Lakeshore Migration Corridor IBA, Harrington Beach State Park IBA, and Ozaukee Bight Migration Corridor. This is the major inland USA corridor for fall-migrating Merlin and Peregrine Falcon; other raptors occurring in smaller, but significant numbers include Rough-legged Hawk, Red-tailed Hawk, Sharp-shinned Hawk, Osprey, and Bald Eagle and owls including Northern Saw-whet Owl and Long-eared Owl. Spring shorebird flights along the shoreline and inland in agricultural fields is significant some springs with large late May concentrations of Black-bellied Plover, Dunlin, Sanderling, Semipalmated Sandpiper, and Ruddy Turnstone. In late summer and fall, 20+ species use the local wetlands and beaches on their passage south. Passerine migration is very heavy both spring and fall along the lakeshore and for some distance inland (up to 3 to 7 miles in some locations). The Point Beach IBA is the largest coastal stopover site between Door County, Wisconsin and the parks and preserves of northeastern Illinois and as such is an extremely important refugium.
Dominant bird groups / species: waterbirds, shorebirds, raptors (Northern Harrier, Osprey, Merlin, Peregrine Falcon), migrant passerines.
**Upper Mississippi River
(from Prescott to Illinois state line—an IBA runs from junction with Chippewa River to the Illinois state line):
Major documentation for considering this corridor as an IBA include raptor migration (buteos, both eagle species including wintering birds and breeding Bald Eagles, Osprey, breeding Red-shouldered Hawk, breeding Peregrine Falcon), migrant White Pelican (> 5,000 birds), many colonies of Great Blue Heron, Great Egret, and Green Heron, migrant waterfowl including nationally important concentrations of Tundra Swan, Canvasback, Common Goldeneye, and Bufflehead, numerous bottomland forest breeding passerines including Acadian Flycatcher, Wood Thrush, Kentucky, Cerulean, Prothonotary, and Hooded Warbler, and Louisiana Water-thrush.
Dominant bird groups / species: waterfowl, waterbirds, raptors (eagles, Osprey, Turkey Vulture, Peregrine Falcon), passerines.
**Lower Wisconsin River
(from the dam just north of Prairie du Sac southwestward to the junction with the Mississippi River):
An IBA includes 86 miles running as far southwest as 6 miles above the junction with the Mississippi River. This quite unspoiled area of numerous state wildlife areas, state parks, and natural areas is an outstanding raptor corridor for migrants (buteos, both eagle species, Northern Harrier, Osprey, and accipiter species) and wintering Bald and Golden Eagles, Rough-legged Hawks, and Short-eared Owls. Wooded bluffs are important sites for wintering Bald Eagles and a few Golden Eagles. Large numbers of waterfowl, particularly diving ducks and geese, utilize this corridor. Species likely vulnerable to collisions with bridges include Yellow-crowned Night Heron, Great Blue Heron, Great Egret, and American Bittern, White Pelican, and various raptors. Many bottomland species of concern breed along this corridor including both cuckoos, Whip-poor-will, Red-headed Woodpecker, Acadian Flycatcher, Wood Thrush, Cerulean Warbler, Worm-eating Warbler, Louisiana Water-thrush, Kentucky Warbler, and Hooded Warbler. The upper half of this area from U.S. 12 to the Blue River Sand Barrens State Natural Area is a priority area for breeding grassland birds including Bobolink, Henslow’s Sparrow, Lark Sparrow, Grasshopper Sparrow, and Western Meadowlark, most of which breed on the sand and gravel terraces along the river bluffs.
Dominant bird groups / species: waterfowl; waterbirds; raptors (eagles, Osprey); passerines.
**St. Croix River
(from Taylor Falls south to Prescott):
This corridor is also defined as the St. Croix River Important Bird Area (IBA). Major documentation for considering this corridor as an IBA include raptor migration (mainly Bald Eagle, Osprey, Turkey Vulture, Red-tailed Hawk, Broad-winged Hawk), waterfowl (geese and diving ducks), several Great Blue Heron colonies, and bottomland forest breeding birds including Red-shouldered Hawk, Prothonotary Warbler, and Louisiana Water-thrush.
Dominant bird groups / species: waterfowl—swans, geese, raptors (eagles, Osprey, buteos, Turkey Vulture); passerines
**Lower Chippewa River
(from junction with Mississippi River upstream for 40 miles):
This corridor is also defined as the Lower Chippewa IBA. Documentation for considering this area as an IBA include breeding Yellow-crowned Night Heron, Red-shouldered Hawk, Bald Eagle (including wintering and migrant birds), Black-billed Cuckoo, Red-headed Woodpecker, Cerulean Warbler, Prothonotary Warbler, and Worm-eating Warbler.
Dominant bird groups / species: raptors (eagles, Osprey); passerines.
Lower Black River
(from junction with Mississippi River upstream for 15 miles):
This IBA runs northeast-southeast and acts more as a stopover site than a migrant corridor. Many bottomland species of concern breed in this valley including both cuckoos, Whip-poor-will, Red-headed Woodpecker, Red-shouldered Hawk, Acadian Flycatcher, Wood Thrush, Prothonotary Warbler, and Cerulean Warbler (identified as a core region for this species). Waterfowl from trempeleau NWR heavily use several miles of the bordering wetlands above the confluence with the Mississippi River for foraging and stopover habitat.
Dominant bird groups / species: Most vulnerable group: waterfowl, passerines.
Western Green Bay shoreline
(from Marinette south along western shore to city of Green Bay):
Four IBAs are located along this stretch of shore including Seagull Bar IBA at Marinette, Lower Peshtigo River IBA, Green Bay West Shore Wetlands IBA , and Lower Green Bay Islands-Bay Beach Wildlife Sanctuary IBA. This corridor is a major fall migration route for raptors including Merlin, accipiters, buteos, and Osprey and an important fall flyway in low water years for shorebirds. Inshore waterbirds include significant concentrations of Double-crested Cormorant, White Pelican, Herring Gull, Ring-billed Gull, Common Tern, Caspian Tern, and a wide variety of waterfowl.
Dominant bird groups / species: waterbirds, raptors (accipiters, Osprey, buteos, falcons, Northern Saw-whet Owl, landbirds
Kewaunee River—East Twin River corridor
(from headwaters of Kewaunee River , Red River Township and headwaters of its tributary Casco Creek, Lincoln Township, Kewaunee County including the adjacent Duvall Swamp 2 miles east of Duvall downstream to Kewaunee Fish and Wildlife Area, Kewaunee Co., then continuing from the south side of the wildlife area along East Twin River to its mouth in Lake Michigan at Two Rivers, Manitowoc Co.).
These two river corridors offer a mostly well-forested corridor paralleling the Lake Michigan and Green Bay shorelines, allowing landbirds birds to move NNW from Lake Michigan to Green Bay in spring and SSE in fall through a largely agricultural region and an alternative route to the Lake Michigan shoreline corridor. The extent to which birds utilize this route is unknown and needs intensive field work. The Kewaunee Fish and Wildlife Area known locally as the Lipsky Swamp has extensive alder, birch, and tamarack stands known for breeding northern birds including Sandhill Crane, Alder Flycatcher, Winter Wren, Brown Creeper, Veery, Northern Waterthrush, Golden-winged Warbler, Nashville Warbler, and Mourning Warbler. At least 25 species of warblers utilize this route. East Twin River is known as a winter waterfowl concentration area at its mouth and in the Michicot area (Tessen, 2000).
Apostle Islands-Chequamegon Bay migration corridor
(from Outer Island in the Apostle Island group south to Ashland) is a noted route for raptors, some shorebirds (on the lake flats in low water years), waterfowl, and large numbers of passerines, especially in the fall. Two IBAs are located here:
Apostle Islands National Lakeshore IBA and Lower Chequamegon Bay IBA. Periodic raptor surveys have indicated substantial numbers of Merlin and Peregrine Falcon occur on the offshore islands in fall while eagles (mostly Bald) follow the shoreline of Chequamegon Bay westward in the spring.
Important flyway for a number of waterbird species including Double-crested Cormorant, Horned Grebe, Red-necked Grebe, Common Loon, Sandhill Crane (flock observed departing Two Harbors beelining it for Wisconsin shoreline west of Apostle Islands at high altitude), Ring-billed Gull, Herring Gull, Bonaparte’s Gull, and for waterfowl including Tundra Swan, Canada Goose, Redhead, Lesser Scaup, Greater Scaup, scoters (3 species), Common Goldeneye, Red-breasted Merganser, Common Merganser, and Bufflehead. A few raptors regularly migrate over inshore waters including Northern Harrier, Bald Eagle, Osprey, Merlin, Peregrine Falcon, and Short-eared Owl. A few shorebirds have been detected regularly migrating over inshore waters including Killdeer, Whimbrel, Dunlin, Marbled Godwit, and Sanderling, but no systematic counts have been conducted to determine how common shorebird migration in inshore waters actually is. Rare gulls such as Sabine’s and Black-legged Kittiwake and Jaegers (3 species) and both Common and Forster’s Tern have regularly been recorded migrating in inshore waters.
Lake Superior (offshore waters >2 miles): little sampled but the following species are known to make flights across Lake Superior: Common Loon, Tundra Swan, Canada Goose, Peregrine Falcon, Merlin, Sandhill Crane (flock observed departing Two Harbors beelining it for Wisconsin shoreline, Marbled Godwit, Red-necked Phalarope, Ring-billed Gull, Herring Gull, Sabine’s Gull, and jaegers (three species).
**Lower St. Louis River--Wisconsin Point corridor
(located in Superior Township along Lake Superior): includes the Wisconsin Point IBA.
A regionally important spring eagle flyway (Bald and Golden Eagle (several thousand Bald Eagles some years) and to a less extent a hawk migration corridor extends in a north-south direction through the city of Superior and crossing the St. Louis River in the vicinity of the US Highway 2 / US 53 bridge towards Duluth. Other raptors using this corridor include Osprey, Turkey Vulture, Sharp-shinned Hawk, Northern Harrier, Red-tailed Hawk and small numbers of falcons. Large numbers of passerines and small numbers of shorebirds follow the shoreline / stopover habitat at Wisconsin Point while significant numbers of geese and diving ducks use the river and St. Louis Bay for staging and migration. A Common Tern colony on Intrastate Island west of the U.S. 2 / US 53 bridge is regionally important. Birds appear to fly under the existing bridge with little chance for collisions except perhaps in inclement weather.
Tessen, D. 2000. Wisconsin’s Favorite Bird Haunts, 4th ed., Wisconsin Society for Ornithology, Inc., De Pere, Wisconsin, 532 pp.
Updated 14 September 2010, Robert P. Russell, Division of Migratory Birds