Find a fall or cascade, or rushing rapid, anywhere upon a clear stream, and there you will surely find its complementary ouzel, flitting about in the spring, dining in the foaming eddies, whirling like a leaf among the foam-bells; ever vigorous and enthusiastic, yet self-contained, and neither seeking nor shunning your company…He is the mountain stream's own darling, the hummingbird of blooming waters, loving rocky ripple slopes and sheets of foam as a bee loves flowers, and a lark loves sunshine and meadows.
- John Muir, The Mountains of California 1894

Called the dipper, the water ouzel, and other common names, the American dipper (Cinclus mexicanus) is an extremely specialized bird species that inhabits mountain streams in the western half of North America. The American dipper has been described as the only true aquatic songbird and is most noted for its odd dipping behavior, as well as its unique ability to live, feed, and play in the rapids and cascades of cool mountain streams throughout western North America. Within its North American range, there are five suggested subspecies of American dipper. Cinclus mexicanus unicolor, also called American dipper, inhabits the western United States and northward into Canada and Alaska.

Besides its unique behavior, the dipper is also an important indicator of water quality. Healthy populations of American dipper indicate healthy stream ecosystems, a relationship that is an invaluable tool in assessing the overall health of our environment. As a water quality indicator species, the health of American dipper populations can also signal impending environmental problems and aid in the prevention of human illness, costly environmental cleanup, and environmental catastrophes.

The Black Hills are described as an "island in a sea of plains." The mountain range, located in western South Dakota and northeastern Wyoming, is nearly two million acres in size and is entirely separated and isolated from other mountain ranges to the west by over 150 miles of grasslands. While its geographic isolation is unique, the biological values of the Black Hills are what truly set the ecosystem apart from others. Essentially an ecological "mixing zone," the Black Hills ecosystem is comprised of species from western, eastern, northern, and central North American environments. As such, the Black Hills supports many disjunct and peripheral populations of fish, wildlife, plant, and invertebrate populations. And, as an isolated mountain ecosystem, the Black Hills have come to support a host of endemic species of fish, mammals, amphibians, reptiles, birds, insects, snails, and plant communities.

Unfortunately, as an isolated mountain ecosystem, the Black Hills are incredibly fragile and extremely sensitive to environmental change. As documented today, over a century of extensive logging, road construction, mining, domestic livestock grazing, private land developments, water developments, and other activities have left the ecosystem on the verge of collapse. Old growth forest is virtually nonexistent, perennial streams suffer from water quality problems, native plants are being replaced by nonnatives, natural disturbance processes are being controlled and/or eliminated, streams have been extensively dammed and diverted, native fish are literally being eaten away by nonnative fish, and developments are replacing large amounts of forest and riparian habitat. These impacts have taken their toll on native species. However, little has been done to curb the ecological destruction.

The American dipper is at the eastern edge of its global distribution in the Black Hills. The bird is also a permanent resident of the Black Hills and has historically been known to inhabit nearly all permanent, fast-flowing streams in the area. It is believed that the presence of American dipper on the Black Hills today is the result of dispersal during the last ice age. At the time, forested water connections between the Black Hills and the Rocky Mountains are believed to have facilitated dipper dispersal. The Black Hills population of American dipper is now believed to be isolated as a result of vicariant events (events that have led to the creation of significant barriers to dispersal). Extensive grasslands, poor quality stream habitat, and the lack of water connections to dipper populations existing west of the Black Hills have all led to the isolation of the species. Research further indicates the American dipper does not normally disperse or migrate long distances and is very unlikely to move between geographically separated areas. Preliminary data for the population of American dipper on the Black Hills indicates that broadscale movements (i.e., between geographically isolated areas) do not occur.

Populations of American dipper have declined sharply on the Black Hills in the past decade. This decline has been attributed to poor water quality, habitat degradation, reduced or erratic flows in streams, and lack of suitable nesting habitat. Much of the bird's formerly occupied habitat on the Black Hills is now considered sink habitat (habitat that is unable to support the long-term survival of populations) thus presenting serious limitations upon the success of local dispersal and reestablishment. Overall, breeding American dippers have disappeared from nearly 86% of their historical range in the Black Hills. The bird has been listed as Threatened by the State of South Dakota since 1996.

As early as 1993, the U.S. Fish and Wildlife Service ("USFWS") had taken an interest in the status of the American dipper on the Black Hills. The South Dakota Field Office of the USFWS sought to "Conduct status surveys of the American dipper in the Black Hills" in the early nineties. This request was made "…to initiate recovery and management actions for species before the trouble or precipitous declines begin." Similar requests were also made in 1996. However, the agency never completed status surveys for the American dipper on the Black Hills nor did the agency take action before the "trouble" and "precipitous declines" of the American dipper population in the Black Hills.

The Black Hills population of American dipper meets the USFWS's criteria for classification as a distinct population segment ("DPS") under the ESA. The Black Hills population of American dipper is physically and ecologically isolated from other populations to the west and is therefore discrete. Furthermore, the Black Hills population of American dipper persists in an ecological setting that is unique to the species and the loss of the population would result in a significant gap in the range of the taxon. The Black Hills population of American dipper is therefore significant.