The smallest wilderness area in the National Wilderness Preservation System is the five and half acres Pelican Island Wilderness in Florida. This wilderness area is managed by the US Fish and Wildlife Service. The waters surrounding Pelican Island provide abundant food for the area's wading birds who nest on the wilderness island, including great blue herons, white ibis, anhingas, and oyster catchers.

The largest wilderness area in the National Wilderness Preservation System is the Wrangell-St. Elias Wilderness, protecting more than nine million acres of Alaskan tundra and boreal forest. This NPS-managed wilderness area is home to many different animals including Dall sheep, grizzly bears, caribou, wolves, and wolverines.