Written collaboratively by Adam Janke, Joshua Stafford, and Roger Gates (former SDSU Extension Rangeland Management Specialist).
Prairie Pothole Formation
The rapid retreat of the Wisconsin Glacier 10,000 years ago left behind fertile soils that support eastern South Dakota’s thriving agricultural industry, as well as nearly 1 million small depressions in the land, commonly known as Prairie Potholes, sloughs, or wetlands. These wetlands provide many benefits including flood control, groundwater recharge, watering sources for livestock, hay supply in drought years, and countless benefits to South Dakota’s rich wildlife resources.
The Duck Factory
Prairie pothole wetlands are so important to ducks that the area where they’re found, which comprises portions of South Dakota, North Dakota, Minnesota, Iowa, and southern Prairie Canada, is commonly called North America’s Duck Factory. Together with the native grasslands that often surround prairie potholes, these ecosystems play host to nearly half of all the nesting ducks counted in North America annually. This important breeding habitat has caught the eye of duck conservationists since the early 1900s when widespread efforts to keep nesting grassland and wetlands from being converted to row crop efforts began, and are still ongoing today. In addition to their role for nesting ducks though, prairie potholes are also thought to be invaluable resources for migrating ducks as they fly through South Dakota on their way to nesting habitats in Alaska or Canada’s Boreal Forest. These stopping-over birds have a difficult trip ahead, needing to feed enough to handle the marathon-like migratory flights and to preserve the strength to grow, lay, and incubate eggs after they arrive at higher latitudes.
Duck Habitat Research
SDSU researchers sought to understand what migrating ducks needed from South Dakota’s wetlands and whether a suitable supply was available. Wetlands were studied over 4 years with the cooperation of over 300 South Dakota farmers, ranchers, and landowners, to measure aquatic insect food available for and the abundance and health of migrating ducks. The study was done in prairie potholes in crop fields and those in grasslands or pasture to see if those in crop fields were somehow impaired because of sediment, nutrient, or pesticide inputs from surrounding land use practices. No variation was found among wetlands in crop fields when compared with similar wetlands in grasslands, suggesting that wetlands in crop fields provided important habitats for ducks migrating through South Dakota. The key factor that seemed to influence the quality of a prairie pothole for migrating ducks was not the surrounding land use, but rather what other creatures occupied the wetland with the ducks: specifically, fathead minnows.
Impacts of Fathead Minnows
Ducks in poor health tended to occur on wetlands with abundant fathead minnows in them. Ducks weren’t eating fathead minnows, so impacts on duck health resulted from the complex way fathead minnows reduce the abundance of aquatic insects and plants that ducks eat in wetlands. Previous research had found that fathead minnows change wetland water quality from a clear, vegetated state to a cloudy, muddy state with few aquatic plants after they become abundant. This research from SDSU found that those changes in the wetlands resulting from high fathead minnow densities had impacts on ducks passing through the state on their way to distant breeding areas.
Conserving wetland habitat
This research suggested that prairie wetlands in crop fields are still vitally important habitats for ducks so long as the ducks’ competitor – fathead minnows – are kept out. Limiting release for bait production and reducing artificial connections between wetlands through drainage ditches will minimize presence of fathead minnows and ensure wetlands continue to grow the plants and aquatic insects ducks need. With these changes, South Dakota’s prairie potholes can continue to make important contributions to north-bound ducks every spring as they prepare to raise the next generation of ducks to return in the fall.