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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 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 waterfowl, shorebirds, or marshbirds.
“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 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 developers. These 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 marked with two asterisks (**) 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.
The Mississippi River in Iowa is one of the major national waterfowl corridors in the interior of the country. Raptor migrations often are diffuse across the landscape but at times major flights move along the main north-south river corridors. West-east flowing rivers across Iowa such as the Upper Iowa River act more as migration stopover sites than as corridors although the Iowa, Wapsipinicon, Des Moines, and Cedar Rivers are very important passerine corridors during both spring and fall. Large flights of White Pelican, Double-crested Cormorant, waterfowl, and shorebirds often move along the major rivers of the state, stopping over on suitable islands, pools, or reservoirs.
**Upper Mississippi River
(from Minnesota state line to Missouri state line)
Major documentation for considering this corridor as an Important Bird Area (IBA) include raptor migrations (Turkey Vulture, accipiters, buteos, both eagle species including wintering birds with several known roosts and breeding Bald Eagles, migrant Osprey, breeding Red-shouldered Hawk), migrant White Pelican (> 5,000 birds), many colonies of Great Blue Heron, Great Egret, and Green Heron, migrant waterfowl including nationally important concentrations of Bufflehead, Canvasback, Redhead, and Lesser Scaup, numerous bottomland forest breeding passerines including Acadian Flycatcher, Wood Thrush, Kentucky, Cerulean, Prothonotary, and Hooded Warblers, and Louisiana Water-thrush. Several distinct IBAs are located along the river. From north to south are the following: Upper Mississippi River Fish and Wildlife Refuge, Fish Farm Mounds and Lansing State Wildlife Area, Yellow River Forest / Effigy Mounds National Monument north of Marquette, Pikes Peak State Park above McGregor, Green Island Wildlife Management Area near Twin Springs, Jackson County, and Pool 19 from Keokuk north to Fort Madison. The latter location often holds one of the most significant national concentrations of Canvasback, and Lesser Scaup, often 100,000+ birds in the fall. Other species with notable stopover peak concentrations include Ruddy Duck, American Coot, Ring-billed Gull, and Herring Gull. A winter concentration of 350-400 Bald Eagles often concentrate in winter below the Keokuk dam.
Dominant bird groups / species: waterbirds (especially White Pelican), waterfowl, raptors (Turkey Vulture, Bald Eagle, Osprey, accipiters), passerines.
**Big Sioux River
(from junction with Missouri River at Sioux City north to the Minnesota border):
Includes the 3,000 acre Broken Kettle Grassland IBA. Although limited in density compared to eastern Iowa riverine corridors, the Big Sioux (along with the Missouri River) is believed to be the major corridor for passerines in the northwestern half of the state and is an important raptor flyway.
Dominant bird groups / species: raptors (Bald Eagle, Osprey, accipiters, buteos), passerines.
(South Dakota state line to Missouri state line):
Several IBA’s are located along this stretch of river including Badger Lake Wildlife Area, Hitchcock Nature Center, Lake Manawa State Park (White Pelican, Double-crested Cormorant, Bald Eagle, Franklin’s Gull), DeSoto National Wildlife Refuge (500,000+ Snow Geese stopover in spring, major eagle roosts in winter, early spring), the Mid-American Energy Plant in Council Bluffs (breeding Least Tern and Piping Plover, both threatened), Snyder and Winnebago Bends IBA in Woodbury County (breeding Least Bittern, breeding Black-billed Cuckoo and Wood Thrush), and Waubonsie State Park in Fremont County (breeding and migrant passerines including Whip-poor-will, Black-billed Cuckoo, and Wood Thrush). Steep topography and difficulty in row crop farming have resulted in high quality remnant prairie in much of the area. Raptor surveys at the Hitchcock Nature Center have recorded between 5,700 and 8,400 birds annually in the fall of up to 19 species including Bald and Golden Eagle, Osprey, Swainson’s Hawk, Red-tailed Hawk, and accipiter species. This corridor is likely the main north-south corridor for forest passerines on the eastern Great Plains based on number of species recorded and available stopover habitat.
Dominant bird groups / species: waterbirds, waterfowl (geese, raptors (Bald Eagle, Osprey, accipiters), shorebirds (25+ species including Hudsonian Godwit, Buff-breasted Sandpiper, dowitchers), gulls (especially Franklin’s Gull), Black Tern, migrant passerines.
**Des Moines River
(Missouri line north to Fort Dodge):
Includes the Red Rock Reservoir IBA (major wintering site for Bald Eagle and waterfowl stopover, also important for migrant raptors such as Broad-winged Hawk, Osprey, gulls, shorebirds, and breeding warblers such as Cerulean Warbler along its forested shores), Chicaqua Bottoms Greenbelt IBA in Jasper and Polk Counties (waterbirds, waterfowl, shorebirds) and the Shimek Forest IBA in Van Buren and Lee Counties in the extreme southeast. This corridor is well-forested in many spots and offers a major pathway for migrant and breeding passerines in central Iowa.
East Fork of the Des Moines River
(junction with Des Moines River just south of Dakota City, Humboldt County north to Union Slough National Wildlife refuge)
Is a narrow forested corridor and likely good for migrant passerines spring and fall and probably raptors but no extensive documentation of its migratory use has been undertaken to date. Some areas along this corridor were apparently not forested historically save for scattered cottonwoods. Restoration efforts along this stretch might target restoring wet prairie and cordgrass meadows which were historically present and provided habitat for migrant rails and sparrows such as LeConte’s and Nelson’s Sparrows.
(from Rowan in Wright County south to junction with Mississippi River north of Oakville, Louisa County):
This well-forested corridor provides suitable habitat and passageway for migrant raptors (accipiters, Red-shouldered Hawk, Broad-winged Hawk, Bald Eagle) and migrant and breeding passerines including breeding Wood Thrush and Cerulean Warbler. Important bird areas along this corridor include: Iowa River Corridor in Iowa County (breeding grassland birds including Northern Harrier)and Coralville Reservoir/Hawkeye Wildlife Area/Lake McBride State Park in Johnson and Iowa Counties (waterbirds—especially White Pelican and heronries, waterfowl, shorebirds, breeding Bald Eagles, wintering Northern Harrier, Short-eared Owl, and Long-eared Owl, and migrant passerines;
Dominant bird groups / species: White pelican, waterfowl, raptors, migrant passerines.
(from junction with Iowa River at Fredonia, Louisa County north to Cedar Lake at Nashua, Chickasaw County):
George Wyth State Park/Hartman Reserve in Black Hawk County (breeding Red-shouldered Hawk, major migrant passerine stopover site), Wickiup Hill / Cedar River complex in Linn County (breeding Bald Eagle and Red-shouldered Hawk, breeding grassland passerines such as Loggerhead Shrike, Bobolink, and Grasshopper Sparrow, and both breeding and migrant forest passerines including Black-billed Cuckoo, and Cerulean Warbler), Cedar Valley Nature Preserve Trail (breeding Bell’s Vireo, Lark Sparrow, and Grasshopper Sparrow and migrant Broad-winged Hawk spring and fall), Swamp White Oak Preserve in Muscatine County (breeding Bald Eagles, Red-shouldered Hawk, Yellow-billed Cuckoo, Yellow-throated Vireo, and Orchard Oriole and important forest/oak savanna bird stopover habitat). The Nature Conservancy has established the Lower cedar River as a priority area for protection in Iowa with over 20,000 acres protected under various conservation efforts.
Dominant bird groups / species: raptors, migrant passerines
(from junction with Mississippi River north of Princeton, Scott County north to Minnesota state line):
IBAs includes the Wapsipinicon River Greenbelt in Bremer County (breeding Red-shouldered Hawk, American Bittern, Least Bittern, Black-billed Cuckoo, Veery, Wood Thrush, Cerulean Warbler, and grassland birds such as Grasshopper Sparrow and Bobolink) and several other state parks and wildlife management areas.
Dominant bird groups / species: waterbirds, raptors, migrant passerines
Other Potential Corridors
Other relatively short stretches of rivers in Iowa can be utilized by birds as migration corridors. The Nishnabotna River (including the West and East Branches and their branches) from the Missouri state line in Fremont County north to its various headwaters is reported to be a landbird migration corridor but needs further study.
Waterfowl corridors such as various chain-of-lakes and close proximity large lakes and reservoirs acting as stepping stones for migrant ducks and geese exist in the prairie pothole (Des Moines Lobe) portion of the state, but have not been mapped to date.
Vulnerability means the potential for a select group of species to collide with man-made structures including bridges, communication towers, and buildings.