The peak migration occurs in late May when 5,000 or more ducks may be present. Canada geese have been reestablished in North Park and begin nesting on the refuge during April. Duck nesting usually starts in early June and peaks in late June. The refuge produces about 9,000 ducklings and 150 to 200 goslings each year. When refuge lands are fully acquired and developed, waterfowl production should increase significantly.
Primary upland nesting species include the mallard, pintail, gadwall, and American wigeon.
A number of diving ducks, including the lesser scaup and redhead, nest on the larger ponds and adjacent wet meadows. Most species may be observed during the entire summer season. Fall migration reaches its height in late September or early October when up to 8,000 waterfowl may be on the refuge. Refuge wetlands also attract numerous marsh, shore, and water birds. If they are present, Wilson's phalarope, American avocet, willet, sandpipers, yellowlegs, and dowitchers will be easy to observe.