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Wisconsin State Natural Areas Program Fourmile Island Rookery (No. 41)

Artificial nesting platforms at Fourmile Island

Photo by Joshua Mayer



Within Horicon Wildlife Area, Dodge County. T12N-R16E, Section 19. 25 acres.



Situated with Horicon Marsh, Fourmile Island contains one of the largest heron and egret rookeries in the Midwest. The narrow island is forested with large oaks, basswood, elm, aspen, and cottonwood--trees used for nests by great blue herons, black-crowned night herons, and great egrets. A July 1984 windstorm toppled nearly 80 trees. This, along with Dutch elm disease and the effects of heron guano, has reduced the number of trees and therefore the nesting habitat in recent years, although a January 1985 inspection showed nearly 500 trees still suitable as nest sites. The numbers of birds fluctuate from year to year although it appears that current numbers are down from historical highs. Fourmile Island Rookery is owned by the DNR and was designated a State Natural Area in 1965.


Driving directions

THE ISLAND IS CLOSED TO ALL PUBLIC USE APRIL 1-SEPTEMBER 15. Contact the State Natural Areas Program for more information.


Fourmile Island Rookery is owned by:

  • WDNR


Site objectives

Manage the site as a heron rookery and a breeding bird conservation site. Natural processes, especially guano deposition, determine the structure of the above ground natural communities. Augmentation of habitat by constructing nesting poles appropriate for use by heron species is a desirable management practice. Provide opportunities for research and education.

Management approach

On the island, the native dominant tree species (primarily maples and oaks) are managed passively. Death of trees and shrubs due to guano deposition may occur as long as herons use the site.

Site-specific considerations

  • Construction of nest poles adjacent to the guano-killed tree area permits gradual recovery and long-term use of the island as a rookery.
  • Access is prohibited during heron nesting season (April 1 through September 15).


Management objectives and prescriptions

  • This site is currently in the master planning process as part of the Horicon-Shaw Planning Group master planning effort.
Last revised: Thursday, October 19, 2017