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Diurnal Avian Corridor Maps
Identify river systems and other geological features that are valuable diurnal avian migration corridors.
All major river 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.). East-west 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 most species’ spring or fall migration patterns. One examples of this pattern would be the Sauk River in Stearns County which generally flows west to east until it joins the Mississippi River at Sauk Rapids. Simultaneously, the state’s IBAs associated with a river system were mapped. 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 within a mile of either bank of the waterway or continuous gallery forest along its banks. Selected river corridors required a minimum of 50% forest patches or gallery forest along at least one bank of a stretch of a waterway for inclusion. In some cases, portions of the corridor which did not meet these criteria were eliminated from further consideration. In a few instances in heavily agricultural landscapes, blocks of forest habitat were patchily distributed along the banks or within one mile of the waterway, but were likely visible to migrating forest birds from one patch to the next and were included. In other instances, substantial wetlands along the banks or within a mile of a waterway indicated a potentially valuable corridor for shorebirds or marshbirds and were included.
“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 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 double 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 the potential height of any bridge constructed which may prove to be a hazard for migrant and resident birds.
The first three sites below (marked with **) have the highest probability of potential bridge-avian collisions based on the topography of the river valley and the existence of species which may be most vulnerable to such collisions. The other corridors contain significant concentrations of birds, but are not thought to have the highest potential for avian collisions with bridges. They may, however, have high potential for avian collisions with other structures such as buildings, communication towers, and wind turbines.
Upper Mississippi River **
(from Little Falls to Iowa state line)
Various IBAs run from Monticello all the way to the Iowa border and include from north to south the following: North Metro Mississippi River IBA, Mississippi River Twin Cities Important Bird Area, Lake Pepin IBA, a portion of the Vermillion Bottoms-Lower Cannon River IBA, and the Upper Mississippi NWR IBA. Major documentation for considering this corridor as an IBA include raptor migration (buteos, Turkey Vulture, both eagle species including wintering birds and breeding Bald Eagles, Osprey, breeding Red-shouldered Hawk, breeding Peregrine Falcon), migrant White Pelican (> 5,000 birds), colonies of Great Blue Heron, Great Egret, and Green Heron, migrant waterfowl including nationally important concentrations of Tundra Swan, Canvasback (Weaver Bottoms), Common Goldeneye (Lake Pepin), and Common Merganser (Lake Pepin), numerous bottomland forest breeding passerines including Acadian Flycatcher, Wood Thrush, Kentucky, Cerulean, Prothonotary, and Hooded Warbler, and Louisiana Water-thrush. The bordering and island bottomland forests and adjacent bluff forests are a very important stopover site for spring and fall passerines from St. Cloud southward.
Most vulnerable groups: waterfowl (especially Tundra Swan, diving ducks, mergansers), waterbirds (herons, egrets, White Pelican), raptors—eagles, Osprey, Turkey Vulture, Peregrine Falcon, passerines.
St. Croix River**
Waterbirds, mainly from Taylor Falls south to Prescott; raptors and landbirds from Wisconsin—Pine County, Minnesota boundary south to Prescott: a portion of this corridor is also defined as the St. Croix River Important Bird Area (IBA) on the Wisconsin side of the river while the St. Croix Bluffs IBA has been designated on the Minnesota side in Washington County. Major documentation for considering this corridor includes raptor migration (mainly Bald Eagle, Osprey, Turkey Vulture, Red-tailed Hawk, Broad-winged Hawk), waterfowl (Trumpeter Swans, geese and diving ducks), several Great Blue Heron colonies, and bottomland forest breeding birds including Red-shouldered Hawk, Prothonotary Warbler, and Louisiana Water-thrush. This corridor is also an important pathway for migrant landbirds spring and fall
Most vulnerable groups: waterfowl—Trumpeter Swan, geese, raptors (eagles, Osprey, buteos, Turkey Vulture); passerines.
Minnesota River Valley**
Segment 1-(Browns Valley, Traverse County southeast to Mankato): this corridor is used primarily by migrant waterbirds (especially White Pelican), waterfowl, raptors (accipiters, Red-tailed Hawk, Bald Eagle) spring and fall, and landbirds, especially swallows, warblers, and vireos. The Lac Qui Parle—Big Stone IBA documents avian concentrations in a portion of this river stretch.
Most vulnerable groups: waterbirds (White Pelican), waterfowl, raptors (Turkey Vulture, Osprey, buteos, and Bald Eagle), migrant landbirds.
Segment 2-Mankato north and east to the junction with the Mississippi River at Fort Snelling): this corridor is an important waterfowl pathway and stopover area for Tundra Swan and ducks spring and fall, for fall raptors, especially Turkey Vulture, Osprey, buteos, and Bald Eagle, and for migrant and breeding landbirds including both cuckoo species, Wood Thrush, 25+ species of warblers, and Lark Sparrow. The Upper Minnesota River Valley IBA and the Lower Minnesota River Valley IBA document avian concentrations in this river stretch.
Most vulnerable groups: waterfowl, raptors (Turkey Vulture, Osprey, buteos, and Bald Eagle), migrant landbirds.
Lake Superior shoreline
(from Pigeon River/Canadian border southwest to Park Point, Duluth): likely the most important migratory corridor in the state for 200+ species of migratory birds. Two individual IBAs are located along the shoreline, namely (from north to south, North Shore Peregrine Falcon Eyries, Hawk Ridge Nature Reserve IBA): This is the major western Great Lakes corridor for fall-migrating raptors including Rough-legged Hawk, Northern Goshawk, Sharp-shinned Hawk, Golden Eagle (200+ birds in fall), Osprey, Bald Eagle (3,000+ birds spring and fall) and owls including Northern Saw-whet Owl and Long-eared Owl. Spring shorebird flights along the shoreline are usually low but fall numbers of American Golden Plover (Hawk Ridge-Duluth) and Sanderling (Park Point-Duluth) can reach dozens to several hundred birds. 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) with many fall birds moving along the ridgetops. The density of the fall raptor flight increases as one moves southwestward from Grand Portage as birds coming in from the west, hit the coast, and join other birds already moving southwardwest along the coast (Gerald Nieme, pers. comm., 2009).
Most vulnerable groups: raptors-accipiters, buteos, Osprey, both eagle species, Long-eared Owl, Northern Saw-whet Owl, passerines.
St. Louis River
(from its mouth at Duluth Harbor upriver to Fond du Lac): the eastern portion of this corridor in the vicinity of the U.S. Highway 53 bridge is the major spring raptor pathway for accipiters, buteos, Golden Eagle, Bald Eagle, and Osprey in Minnesota. Depending upon winds this pathway may move eastward over Lake Superior (for eagles), more often westward a couple of miles. Many species use this corridor, notably White Pelican, Sandhill Crane, Common Loon, Northern Raven, Blue Jay, and swallows.
Most vulnerable groups: waterbirds (Common Loon, Sandhill Crane), raptors (Bald Eagle, Osprey)
Red River Valley
(from the Canadian border north of St. Vincent, Kittson County south to Browns’s Valley, Traverse County): although not a well-studied corridor, this river valley serves as a minor raptor (<5,000 raptors per season) route and as a major waterfowl (swans, ducks, geese) route, often attracting tens of thousands of waterfowl during the frequent spring flood years. Based on years of anecdotal data from birders in the Fargo-Morehead and Crookston-Grand Forks area, this is also an important corridor for migrant forest landbirds spring and fall, the most significant pathway between the Mississippi River to the east and the James River in the Dakotas to the west. Despite some channelization and forest fragmentation in the southern portion of the valley, where in some places the bordering “forest” is only one tree wide, most of the remaining stretches are bordered by at least some forest cover as far north as the Canadian border. Several studies have shown that this river valley also lies in an important shorebird pathway for over 20 species of boreal or Arctic-breeding species. Most of this migration is nocturnal with stopover sites determined by the presence of floodwaters or exposed flats from drawdowns or droughts. Some diurnal fall shorebird migration has been noted for plovers and Buff-breasted Sandpiper at very low altitudes, but whether this is typical is unknown and needs further study.
Most vulnerable groups: waterfowl, raptors (Osprey, accipiters, buteos, and Bald Eagle), migrant landbirds.
Des Moines River Valley
(from Petersburg Township at the Iowa state line northwest to Windom, Cottonwood County): this forested stretch offers a suitable pathway for migrant landbirds, especially cuckoos, vireos, flycatchers, thrushes, and warblers. A few raptor migration observations have been made in this largely unstudied corridor indicating the presence of at least a minor (5,000 birds) raptor migration route spring and fall for accipiters and buteos (Broad-winged Hawk, Red-tailed Hawk).
Other Potential Corridors
Other relatively short stretches of rivers in Minnesota can be utilized by birds as migration corridors. The Red Lake River from Crookston, Polk County northwest to its junction with the Red River at East Grand Forks, the Buffalo River (see Bluestem Prairie—Buffalo River IBA) in Clay County from Silver Lake northwest to its junction with the Red River near Georgetown, and the Blue Earth River from Mankato south to Elmore, Faribault County on the Iowa state line are all reported to be landbird migration corridors but need further study. The Marsh River in Northwest Norman County from Anthony northwest to its junction with the Red River near Shelly has a forested corridor along its banks and is likely a landbird corridor but needs additional study. Many waterfowl corridors such as various chain-of-lakes and close proximity large lakes acting as stepping stones for migrant ducks and geese exist throughout many portions of the state but have not been mapped out to date.
The southern (and sometimes eastern and western) shores of the larger lakes such as Mille Lacs, Leech (see Mille Lacs IBA), Minnetonka, Upper and Lower Red Lake, Vermilion Lake, Lake Winnibigoshish, and Lake of the Woods (see Lake of the Woods IBA) often act as local concentration areas and/or corridors for migrant landbirds in spring. The literature seems to be absent on whether the reverse is true in the fall for northern shores, although anecdotal data indicates that at least some western shorelines such as Mille Lacs can be used by many landbirds.
Vulnerability means the potential for a select group of species to collide with man-made structures including bridges, communication towers, and buildings.