The North American counterpart of our Common Pochard Aythya ferina, the Redhead A. americana breeds across the Prairie Pothole Region. It winters predominately in coastal areas along the Gulf of Mexico. Vagrants occasionally reach Europe.
The Prairie Pothole Region is an area of the northern Great Plains and midgrass and tallgrass prairies that contains thousands of shallow wetlands known as potholes. These potholes are the result of glacier activity in the Wisconsin glaciation, which ended about 10,000 years ago. The decaying ice sheet left behind depressions formed by the uneven deposition of till in ground moraines. These depressions are called potholes, glacial potholes, kettles, or kettle lakes. They fill with water in the spring, creating wetlands which range in duration from temporary to semipermanent. The region covers an area of about 715000 km2, including parts of three Canadian provinces and five U.S. states. Few natural surface water drainage systems occur in the region; pothole wetlands are not connected by surface streams. They receive most of their water from spring snowmelt. Some pothole wetlands also receive groundwater inflow, so they typically last longer each year than those that only receive water from precipitation. Shorter-duration wetlands fed only by precipitation typically are sources of groundwater recharge.