Birds of the St. Croix River Valley: Minnesota and Wisconsin
Abstract
The St. Croix River Valley encompasses nearly 11,550 km2 in east-central Minnesota and northwestern Wisconsin. A wide range of habitats are available for birds including upland oak, lowland deciduous, maple-basswood, lowland and upland coniferous forests, natural basin wetlands, and grasslands. Situated in the north-central region of the United States, the valley is a biological "crossroads" for many species. Because of the mixed affinities of plant communities, the valley includes the northern and southern range limits for a number of species. Also, because the valley lies near the forest-prairie transition zone, many typical western breeding species (e.g. pintail, western meadowlark, yellow-headed blackbird) breed in proximity to typical eastern species such as tufted titmouse, eastern meadowlark, and cardinal.
From 1966 to 1980, I conducted extensive surveys of avian distribution and abundance in the St. Croix River Valley. I have supplemented the results of these surveys with published and unpublished observations contributed by many ornithologists. These additional data include compilations from Christmas Bird Counts sponsored by the National Audubon Society and from the Breeding Bird Survey coordinated by the U.S. Fish and Wildlife Service. Three hundred fourteen species have been recorded in the study area; data are presented on the migration period, nesting season distribution, winter distribution, relative abundance, and habitat use of each species.
Recognizing the uniqueness of the area, and its importance not only to wildlife but also to man, the U.S. Congress designated the St. Croix a National Scenic Riverway. This action provided a considerable degree of protection to lands along and directly adjacent to the river. Unfortunately, no similar legal measure exists to protect lands away from the river. With the exception of the northern quarter of the St. Croix River Valley, agricultural interests have made significant inroads into the habitat base. The continuing expansion of the nearby Minneapolis-St. Paul metropolitan region has degraded or destroyed many woodlots, upland fields, and wetlands. In numerous instances, degradation of natural habitats has influenced the abundance and distribution of bird species. Because of these changes, both the Federal government and State Departments of Natural Resources have listed several species in various categories based on their current status. In the St. Croix River Valley, seven species are endangered, eight are threatened, and 29 are watch or priority status in either or both states. Data presented in this report are of value to land managers, land use specialists, and ornithologists, in assessing current and projected habitat alterations on the avifauna of this valley.
The St. Croix River bisects a large region of western Wisconsin and east central Minnesota that exhibits a wide range of habitat types. This region supports not only birds, but many mammals, fishes, reptiles and amphibians, and several thousand species of vascular and nonvascular plants. The river itself is relatively clean through most of its course, and its natural flow is interrupted by only two small dams.
Because the river lies within a 1-day drive of nearly 10 million people (Waters 1977), use of the area for recreational purposes is extremely heavy. Recreational pursuits include sunbathing, boating, and wild river kayaking in the summer, and ice fishing and cross-country skiing in the winter. The large number of unique and highly fragile habitats that exist there may never be compatible with the uses and abuses of the land that go with expanding human populations.
Through the efforts of a number of citizens concerned with the quality of their environment and the foresightedness of several local, State, and Federal legislators, a portion of the upper St. Croix River Valley (hereafter termed "the Valley") was established as a National Wild and Scenic River. Through establishment of the National Wild and Scenic Rivers Act (P.L. 90:542), the ground rules were established to preserve free-flowing streams that have "outstandingly remarkable scenic, recreational, geologic, fish and wildlife, historic, cultural, and other similar values." Any person who has spent time along a stretch of the St. Croix would have to agree that this river meets or exceeds all the criteria that the Act established.
The history of this magnificent valley is cloaked with the adventures of lumber barons, trappers and hunters, commercial fishermen, and many others. During the days of the early voyageurs, the river served as a vital link between the Great Lakes and the growing Minneapolis-St. Paul area. Excellent descriptions of the colorful history of the Valley are provided by Link (1977) and Waters (1977).
Although the Scenic River Act provides considerable protection for the lands and resources directly adjacent to the river, there is no comparable legal measure to protect lands not bordering the river. Several man-influenced impacts are escalating in the Valley and provide a continual threat to remaining resources. Two influences providing the greatest threat to the natural resources of the Valley are urban expansion and agricultural production. First, the continual, almost unabated spread of urban development has already had a profound impact on existing habitats. Second, agriculture has had a growing impact on bird life in the Valley. Lands producing row crops, small grains, and hay in St. Croix County in 1967 totaled 75,910 ha. This acreage increased 17.4% to 88,057 ha by 1977 (U.S. Department of Agriculture, personal communication). The total hectarage of lands in agricultural production (row crops and hay) made up 16 and 18.8% of the Valley in 1967 and 1977, respectively. These examples suggest the magnitude of the impact that agriculture has had upon wildlife resources in the past two decades.
It can be argued that the agricultural hectarages cited above represent changes in cropping practices rather than actual increases in the hectarage of wildlife habitat converted to agricultural production. However, increased technology and the growth of agribusiness have resulted in a shift to fencerow to fencerow farming with serious impacts on many upland habitats. Wetland habitats have also been significantly reduced. Peterson (1978) showed that over 27% of the seasonal wetlands (Type III of Shaw and Fredine 1956) in St. Croix County were drained between 1958 and 1977.
The objective of this report is to provide, in condensed form, an account of the 314 bird species that have been recorded in the Valley.
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