Fourmile Island Rookery

A narrow island located near the center of Horicon Marsh, Fourmile Island is forested with large oak, elm, basswood, aspen, and cottonwood, which are used by a variety of colonial waterbirds. For over 50 years, the island harbored one of the largest colonial waterbird rookeries in the state with hundreds of nesting pairs of primarily great blue heron, along with egrets, black-crowned night herons and double-crested cormorants. Damage from a 1984 windstorm, along with Dutch elm disease and the effects of heron guano have reduced the available nesting habitat in recent years. Most nesting is currently limited to artificial nesting platforms on the east side of the island. Fourmile Island Rookery is owned by the DNR and was designated a State Natural Area in 1965.