The ponds also produce many insects and other invertebrates needed by most female waterfowl for successful egg laying. These insects also serve as an essential food item for the growth of ducklings and goslings during the summer months.
The first waterfowl arrive in the spring when the ice vanishes in April. 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 during April. Duck nesting usually starts in early June and peaks in late June. The forest produces about 9,000 ducklings and 150 to 200 goslings each year. The Fish and Wildlife Service expects that when refuge lands are fully acquired and developed, waterfowl production should increase significantly.
There have been 198 bird species recorded in the forest.[2] 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 present.
Badger, muskrat, beaver, coyote, and pronghorn are commonly observed. It is also possible to see a raccoon, red fox, mink, long-tailed weasel, or porcupine. As many as 400 mule deer have wintered here and up to 200 elk are frequently seen during the winter months. Moose have recently been reintroduced into North Park and may occasionally be observed in the willow thickets along the Illinois River bottoms. There are no venomous snakes anywhere in this forest.