What: A sprawling network of seasonal lakes, pools, and marshes amid grasslands that supports waterfowl, shorebirds, and prairie species galore. Where: Stretching from Iowa through Minnesota, South Dakota, North Dakota, and northeastern Montana into Canada. When: Early May through mid-June. The spring migration winging north over America’s midsection is often overlooked by birders. Yet some of the continent’s richest birdlife can be found among the ephemeral wetlands of the Great Plains and Upper Midwest. Called the Prairie Pothole Region, this unique ecosystem spans parts of five U.S. states and three Canadian provinces. It’s a little off the beaten path, but with the right preparation, birders who make the trek can expect to see an extraordinary variety of waterfowl, shorebirds, and grassland species in and around these shallow pools and ponds, some of which hold water for mere days in the spring. Around 10,000 years ago, retreating glaciers left behind a...