Horicon Marsh

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When early European settlers came to this land, they settled among the Indian villages and established their first modern settlement - the town of Horicon. In 1846, a dam was built to power a sawmill and develop steamboat navigation. It raised water levels by 3 meters and created Lake Horicon, then considered to be the largest man-made lake in the world. The dam remained for 23 years but was eventually removed to restore marsh conditions and wildlife populations.

The era that followed was one of hunting clubs and market hunting, which lasted into the early 1900s. Over-harvesting decimated waterbird populations and reduced hunting interest, however other interests soon emerged. Moist-soil agriculture, particularly root crop cultivation, provided incentive to drain surrounding lands and eventually the entire marsh. Despite these alterations, farming efforts failed and had ceased by the early 1920s due to the wet springs, heavy rains, and peat soil of Horicon Marsh.

Devoid of water, stripped of wetland vegetation, ditched, tilled, and burned, the marsh was ecologically devastated. In 1921, several conservation-minded individuals began campaigning to restore the marsh. Six years later, the state legislature passed the Horicon Marsh Wildlife Refuge Bill, thereby establishing the state wildlife area. This action authorized dam construction to restore marsh water levels and permitted the acquisition of lands in and around the marsh. Although state funds only acquired one-third of the marsh, federal funds completed the acquisition and led to the establishment of Horicon National Wildlife Refuge in 1941. 

Existing topography/vegetation

Horicon Marsh formed in the late Pleistocene period when a recessional moraine impounded glacial meltwaters. As its outlet eroded, this lake eventually drained and succeeded to an emergent marsh. Today, the agricultural landscape that surrounds Horicon Marsh contains the highest concentration of glacial drumlins in the world. The marsh measures 21 km long and up to 9 km wide and supports a robust aquatic plant community. Throughout the property, native and non-native emergents such as cat-tail, bur-reed, common reed, and reed canary grass are interspersed with open water to create hemi-marsh conditions. Vegetated islands, native and non-native grasslands, and hardwood forests on the property provide habitat for a diverse suite of nesting, foraging, and roosting bird species.

Current management/land use

Horicon Marsh was restored as an emergent marsh following attempts to drain it for agricultural production in the early twentieth century. Currently, the southern one-third of the marsh is a wildlife area managed by the Wisconsin Department of Natural Resources and the northern two-thirds is a wildlife refuge managed by the U.S. Fish and Wildlife Service. Surrounding uplands are in private ownership, largely in agricultural production with some residential development.

A variety of management techniques are used to maintain emergent marsh conditions and thus benefit wetland-associated birds. Water level manipulations create habitat mosaics that support a diverse avifauna, including waterfowl, shorebirds, and waders. Drawdowns begin in early April and are timed so that migrant shorebirds benefit from the lowered water levels and exposed mudflats. At the Refuge, management units are drawn down for two years to control nuisance aquatic species, diversify plant composition within monotypic stands, and provide an abundant seed source.  After the second growing season, water is slowly returned to the unit to coincide with the fall migratory period for shorebirds. Water level management in combination with physical removal, chemical eradication, and native predator introduction (i.e., northern pike) also has been instrumental in carp control and minimizing the ecological damage they cause.

To provide upland nesting habitat for waterfowl and grassland-associated species, Horicon Marsh restored degraded uplands by seeding prairie grasses and forbs native to Wisconsin and by removing tree lines that served as predator corridors. Mowing and prescribed burns are used to control invasive species encroachment in wetland, native prairie, and oak savanna habitats. Other invasive plant control techniques include biological and chemical control, cutting, pulling, mowing, and haying.

Importance to Birds

Horicon Marsh is the largest freshwater cat-tail marsh in the United States. It supports very high concentrations of Mallard, Blue-winged Teal, Gadwall, Northern Shoveler, Green-winged Teal, Ruddy Duck and other migrating ducks. Hundreds of thousands of Canada Geese migrate through the marsh annually, with peak numbers as high as 300,000 occurring in the fall. It also is a significant stopover site for Greater and Lesser Yellowlegs, Semipalmated Sandpiper, Least Sandpiper, Pectoral Sandpiper and other migrant shorebirds. Horicon Marsh hosts the largest breeding population of Redhead east of the Mississippi River as well as significant breeding populations of Least Bittern, American Bittern, King Rail, Forster’s Tern, and Black Tern. For many years, Fourmile and Cotton Islands hosted the largest Great Egret rookery in the state as well as Great Blue Heron and Black-crowned Night-Heron colonies. After nearly 50 years of use, these nesting colonies deteriorated due to natural causes. The Refuge still hosts a Black-crowned Night-Heron colony of approximately 500 birds and American White Pelican recently established nesting colonies on the Main Ditch spoil banks within Refuge boundaries. 

Grassland habitat in the surrounding uplands supports upland-nesting waterfowl such as Mallard and Blue-winged Teal and breeding passerines such as Sedge Wren, Henslow’s Sparrow, Bobolink, and Dickcissel. There is potential to expand these grassland tracts and improve conditions for area-sensitive species by restoring surrounding uplands degraded by agriculture or other anthropogenic activities. Horicon Marsh was designated a Wetland of International Importance under the Ramsar Convention in 1991, a Globally Important Bird Area in 2001, and a Wisconsin Important Bird Area in 2004.

Priority Birds

Species Opportunity Special Habitat Feature
Canada Goose High Forages in open water areas.
Trumpeter Swan Low Rare migrant.
American Black Duck Low Forages in shallow water impoundments.
Mallard High Forages in shallow water impoundments.
Northern Pintail Low Forages in shallow water impoundments.
Blue-winged Teal High Forages in shallow water impoundments.
Canvasback Low Forages in deep water impoundments.
Redhead High Occurs in sparse cat-tail areas.
Red-necked Grebe Low Rare – occurs in vegetated deep water areas.
American Bittern Moderate Found at the Main Pool.
Great Egret High Forages in water levels of 15–30 cm. 
Snowy Egret Low Rare migrant.
Northern Harrier Moderate Nests in upland grass stands.
King Rail Moderate Emergent vegetation in water <46cm deep.
Whooping Crane Low  
American Golden Plover High Forages in agricultural fields and mudflats.
Greater Yellowlegs High Mudflats and shallow, unvegetated water.
Solitary Sandpiper High Mudflats and shallow, unvegetated water.
Whimbrel Low Forages in shallow water <15 cm deep.
Hudsonian Godwit Low Forages in shallow water <15 cm deep.
Marbled Godwit Low Shallow, unvegetated water <15 cm deep.
Buff-breasted Sandpiper High Forages in upland short grasses and mudflats.
Short-billed Dowitcher High Mudflats and shallow water <10 cm deep.
American Woodcock Moderate Breeds in shrubby fields with open area.
Wilson’s Phalarope Low Forages in shallow open water.
Forster’s Tern Moderate Soft-stem bulrush patches in deep water.
Black Tern Moderate Soft-stem bulrush patches in deep water.
Marsh Wren High Nests in cat-tails over standing water.
Sedge Wren High Nests in upland tall grass stands and sedges.
Dickcissel Moderate Nests in upland grass – eruptive population.
Field Sparrow Moderate Nests in hayfields and short grass stands.
Grasshopper Sparrow Moderate Nests in dense upland grass stands.
Henslow’s Sparrow Moderate Nests in mature grassland habitats.
Bobolink Moderate Nests in mature grassland habitats.
Yellow-headed Blackbird High Nests in cat-tail stands over deep water.

Conservation Issues

Water quality is a serious issue within Horicon Marsh and can have many indirect impacts to the bird community. Urban and agricultural runoff enters the marsh through various watershed tributaries and delivers excessive chemicals, nutrients, and sediments into the marsh. This diminishes water quality and can stimulate the germination and growth of dense vegetation, especially cat-tail. Cat-tails effectively take up phosphorus and thus have thrived in the nutrient-rich waters entering the marsh. Non-native carp are abundant and further reduce water quality and habitat diversity by roiling marsh sediments and uprooting aquatic plants. Invasive plant species including reed canary grass, common reed, wild parsnip, purple loosestrife, leafy spurge, common buckthorn, and garlic mustard form monotypic stands in some areas with little wildlife value.

Other conservation issues have more direct impacts to Horicon’s avifauna. Overabundant native predators such as raccoon, opossum, and skunk as well as feral cats impact ground-nesting birds. Many species also are threatened by State Highway 49, a high-speed road that bisects the northern portion of the marsh for 4 kilometers. Bird species with the highest mortality rates include Canada Goose, Least Bittern, American Coot, and Red-winged Blackbird. Frogs, turtles, and muskrats also experience significant adverse impacts (B. Volkert, pers. comm.). The construction of a large wind energy generating facility approximately 2 kilometers from the Refuge poses some risk to bird populations. Cranes, shorebirds, raptors and other bird species commonly fly at relatively low altitudes from the marsh to nearby foraging areas, the proposed locations for turbines. Impacts to bird populations could be significant if a larger buffer zone is not implemented.

Management Recommendations


Information Sources

Information for this account was taken from:

Steele, Y. (ed.). 2007. Important Bird Areas of Wisconsin: critical sites for the conservation and management of Wisconsin birds. Wisconsin Department of Natural Resources Pub-WM-475-2007. Madison, WI.

USFWS. 2007. Horicon and Fox River National Wildlife Refuges Comprehensive Conservation Plan. U.S. Fish and Wildlife Service, Mayville, WI.

Contact Information

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013.
The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.

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