Birds of the St. Croix River Valley: Minnesota and Wisconsin
Wetland Communities
Prairie Wetlands
Much of central St. Croix, southern Polk, north central Washington, and south central Chisago counties are dotted with small semipermanent and permanent wetlands. These wetlands occur on glacial outwash associated with the Wisconsin glacial epoch, which ended about 10,000 years ago. Upland soils associated with these wetlands are highly fertile loams and silt loams which are very important for agricultural production. Related to this, large hectarages of Prairie Wetlands have been drained or seriously altered to facilitate expanding agricultural production.
Principal emergent and submerged aquatic vegetation associated with these freshwater, low-acidity wetlands include hardstem bulrush, softstem bulrush, river bulrush, cattail, cane reed, spikerush, burreed, coontail, and water milfoil. Other important species dependent on water permanence and the degree of acidity include arrowhead, water plantain, and reed canary grass.
Characteristic breeding birds associated with Prairie Wetlands include pied-billed grebe*, American bittern*, Canada goose*, mallard*, gadwall*, pintail*, green-winged teal*, blue-winged teal*, ruddy duck*, Virginia rail*, sora*, American coot*, black tern*, tree swallow*, long-billed marsh wren*, yellow warbler, common yellowthroat, yellow-headed blackbird*, red-winged blackbird*, swamp sparrow, and song sparrow.
Forest Bordered Wetlands
Although similar to Prairie Wetlands in geologic origin, Forest Bordered Wetlands are different in flora and fauna. This community is widespred throughout the area north of the Tension Zone. Forest Bordered Wetlands are usually similar in size, but much deeper than Prairie Wetlands, and the interspersion of emergent and submerged aquatic vegetation is less pronounced. Acidity of the water in Forest Bordered Wetlands is generally greater than in Prairie Wetlands. Principal emergent and submerged aquatic vegetation associated with this community includes cattail, wild rice, iris, pickerelweed, arrowhead, water plantain, bladderwort, elodea, coontail, water milfoil, white waterlily, and yellow waterlily.
Characteristic breeding birds associated with these wetlands include common loon*, green heron, mallard, black duck*, wood duck, ring-necked duck*, hooded merganser, Virginia rail, belted kingfisher, tree swallow, long-billed marsh wren, yellow warbler, common yellowthroat, red-winged blackbird, brown-headed cowbird, swamp sparrow, and song sparrow.
Riparian Habitats
The streams and rivers of the Valley are well known for their recreational attractions. Among the important rivers are the Snake, Kettle, Willow, Apple, Clam, Namekagon, and Kinnickinnic. Numerous small streams that are tributaries of these larger rivers often provide excellent trout fishing. Breeding birds associated with streams and rivers may also be included in larger deciduous and coniferous communities. However, nesting strategies of several species are closely related to certain aspects of the ecology of moving water. Principal among these breeding birds are the great blue heron* (locally), mallard, wood duck*, hooded merganser*, spotted sandpiper*, belted kingfisher*, eastern phoebe*, rough-winged swallow*, cliff swallow*, American robin, yellow warbler, common yellowthroat, red-winged blackbird, and song sparrow.
Northern Sedge Meadow
This community occurs throughout the Valley and makes up a large proportion of the aquatic habitats. These wetlands occur primarily north of the Tension Zone. Northern Sedge Meadow usually forms on the bed of an ancient lake or along and adjacent to larger streams and rivers. Soils associated with this community consist primarily of decaying vegetation and have a low mineral content. Groundwater is usually at or near the surface, providing a spongy texture to the soil surface. Probably the largest and best developed examples of Northern Sedge Meadow are associated with the bed of Glacial Lake Grantsburg in Burnett and Pine counties.
Principal vegetation of this community includes foxtail sedge, crested sedge, inland sedge, slender sedge, tussock sedge, fox sedge, cattail, bluejoint grass, manna grass, and dark-green bulrush. Important forbs include marsh cinquefoil, marsh milkweed, purple-stem aster, marsh bellflower, spotted joe-pye weed, meadow sweet, and small bedstraw.
Northern Sedge Meadows do not support the diversity and abundance of breeding birds usually associated with other wetland types. However, several species breed in this community almost exclusively. Principal breeding species include American bittern, mallard, marsh hawk*, ring-necked pheasant, sandhill crane*, sora, common snipe*, short-billed marsh wren*, yellow warbler, common yellowthroat*, red-winged blackbird, brown-headed cowbird, LeConte's sparrow* (local), swamp sparrow, and song sparrow.
Alder Thicket and Shrub Carr
Both Alder Thicket and Shrub Carr communities are similar in geologic origin and flora. One major difference between these habitats is that alder is replaced by willow, particularly silver willow, in Shrub Carrs. Both habitat types are usually associated with ancient lake beds or the floodplains of streams and rivers. In many instances, these habitats develop from the invasion of woody shrubs in a Northern Sedge Meadow. Alder Thicket and Shrub Carr communities occur regularly throughout the Valley. However, there appears to be a predominance of Alder Thickets north of the Tension Zone, and Shrub Carrs occur most frequently within and south of the Tension Zone.
Principal vegetation associated with the Shrub Carr community includes silver willow and red-osier dogwood in the shrub layer. Common grasses and forbs include marsh shield fern, yellowish sedge, bluejoint grass, reed canary grass, manna grass, marsh milkweed, jewelweed, spotted joe-pye weed, water horehound, and meadowsweet. Characteristic breeding birds of Shrub Carr include mallard, blue-winged teal, marsh hawk, ring-necked pheasant*, common snipe, willow flycatcher*, short-billed marsh wren, veery, yellow warbler*, common yellowthroat, red-winged blackbird, brown-headed cowbird, swamp sparrow, and song sparrow.
Vegetation associated with Alder Thicket habitat includes speckled alder and red-osier dogwood in the shrub layer. Characteristic grasses and forbs include dark-green bulrush, tall manna grass, bluejoint grass, marsh milkweed, marsh bellflower, turtlehead, spotted joe-pye weed, jewelweed, field mint, and great water dock. Characteristic breeding birds of Alder Thicket include alder flycatcher*, tree swallow, gray catbird, veery*, golden-winged warbler, yellow warbler, northern waterthrush* (local), common yellow- throat, red-winged blackbird, swamp sparrow*, and song sparrow.
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