North-South Orientation Effect
There are a large number of birds whose range ends within the Riverway. The best examples are those species where this is the northern or southern limit of their breeding range. A good example is the Prothonotary Warbler whose range extends northward along the St. Croix River to St. Croix Falls, Wisconsin. Indeed, the bird is considered common in the smaller back channels but is unheard of north of St. Croix Falls. Likewise, Hooded Warblers are known to nest along seeps at the base of forested bluffs near Somerset Landing and north of County O Landing on the Wisconsin side of the river south of Grantsburg. These are among the northernmost records of breeding for these birds. Other southern species showing up in small numbers include Great Egret, Acadian Flycatcher, Blue-gray Gnatcatcher (common), Blue-winged Warbler, Cerulean Warbler, Kentucky Warbler (Kinnickinnic State Park), Louisiana Waterthrush (common in its preferred habitat), and Orchard Oriole.
Those Riverway species whose breeding range lies mostly to the north are almost too numerous to list. Many of the warblers typical of the boreal forest can be found in the uppermost portions of the St. Croix and Namekagon rivers. It is here where you can regularly find Alder Flycatchers, Winter Wrens, Northern Parula, Canada Warbler, Black-throated Green Warbler, Northern Waterthrush, Yellow-rumped Warbler, Nashville Warbler, Mourning Warbler, Blackburnian Warbler, Hermit Thrush, White-throated Sparrows, and Evening Grosbeaks (Namekagon River north of Hayward). The rarer species include Blackpoll Warbler, Magnolia Warbler, Connecticut Warbler, Lincoln's Sparrow and Dark-eyed Junco.