Big Stone National Wildlife Refuge

Geology

The refuge lies at the southern extent of what was once glacial Lake Agassiz. About 9,000 years ago, glacial River Warren flowed south from Lake Agassiz, carving out today's Minnesota River Valley and dropping large boulders across the landscape. The glacial river also exposed granite bedrock (gneiss and biotite) estimated to be 2.7 billion years old, some of the oldest known rocks in the world.

Glacial retreat at the end of the Wisconsin glaciation around 10,000 years ago left numerous depressions across the landscape. These "potholes" became shallow, ephemeral wetland basins amidst a sea of grass, across an area now known as the Prairie Pothole Region.

Climate

Big Stone experiences a temperate climate, with warm-to-hot summers and cold winters. Average summer temperatures are 81.6°F with highs above 100°F (maximum recorded temperature of 108°F). Average winter high temperatures are 20°F (minimum recorded temperature of -36°F). Average annual precipitation is 24.08 in and annual average snowfall is 40 in.^[3]

Flora

Wetlands and grasslands represent the dominant cover types at the refuge.

About 4,500 acres of the refuge is covered in wetlands, with cattail as the dominant species.

Of the 5,500 acres of grassland, about 1,700 acres are considered prairie remnants. Wet meadows represent the transition from wetlands to grasslands and have largely been invaded by non-native reed canary grass within the refuge, though a few areas remain dominated by sedges and prairie cordgrass.^[3]

Fauna

Over 250 bird species have been observed in the refuge. The site represents an important migration stopover at the edge of the Mississippi and Central flyways. Audubon Minnesota includes the refuge in its Lac qui Parle-Big Stone Important Bird Area (IBA).^[4] In the spring, upwards of 75,000 ducks and 84,000 geese have been counted. Dominant species include Canada goose, mallard, blue-winged teal, gadwall, green-winged teal, lesser scaup, and ring-necked duck. Big Stone is an important breeding area for grassland bird species of concern including bobolinks and grasshopper sparrows. Black terns commonly nest in wetland areas. Eastern wild turkey were reintroduced to the refuge in 1995 and their population have since reached levels sustainable for hunting. Greater prairie-chickens were reintroduced between 1999 and 2005, but most settled off refuge. A sharp-tailed grouse lek was recorded on the refuge in 2007.^[3]

The refuge has recorded 45 mammal species. The most common species include white-tailed deer, coyote, Eastern cottontail, and several species of squirrel. North American river otter were first reintroduced to Minnesota at the refuge in 1981 and are frequently observed.^[3]

The Dakota skipper is the only federally listed species of the 46 butterfly species that have been observed on the refuge. Other species of concern include the poweshiek skipperling and regal fritillary.^[3]

Other species found on the refuge include 12 reptiles, 8 amphibian, and 35 species of fish.^[3]