How to Spot a Prairie Fen

By Jake McCarthy

The next time you’re out walking in nature and surrounded by sedges with damp feet, take a look around. You might find yourself in a fen, one of Michigan’s most diverse habitats. Prairie fens are nutrient-rich wetlands that use groundwater to support a wide range of plants and animals. Globally scarce, they are home to species including Eastern massasauga rattlesnake and pink and white lady slipper. Fens also improve water quality and reduce the risk of flooding.

Fens are fragile, though, and need to be recognized and protected in order to thrive. MNA protects and manages a number of fens in Michigan, including the Bullard Lake Fen Plant Preserve in Livingston County and the Robert T. Brown Nature Sanctuary in Houghton County. It can take 10,000 years for a fen to form naturally, so it’s important to do what we can to conserve the fens we have.

Here are a few ways to identify a fen:

Soil – Peat and marl are common soil types in fens. Peat, made of decaying plant matter, is spongy and bounces when you walk on it. Marl is a gray-colored and clayish soil.

Water Source – Unlike bogs and swamps, which are rainwater-fed, fens receive water from seeps and springs. Seeps and springs are sources of ground water that have reached the surface. It’s easier to spot both in winter because steady temperatures means they’re unlikely to freeze.

Water Level – The water level in a fen remains fairly constant. Even after a heavy rain, it won’t show significant standing water like a swamp. This is because fens draw water from the ground, not precipitation.

Hummocks – Fens are rife with hummocks, small mounds of sedges that haven’t decomposed because of the water. Hummocks are a great place for a variety of plants to grow, and dot the face of any healthy fen.

For more information on prairie fens in Michigan, how to spot them and restoration tips for landowners, visit MSU’s Prairie Fen Companion website.

To learn more about MNA’s fens and efforts to conserve them, visit our website. To join MNA staff in managing fens with prescribed burns, contact regional stewardship organizer Matt Schultz for more information at


At MNA, our Mission is to protect special natural areas and the rare species that live there. The goals of our blog are to cover the latest environmental issues affecting these areas and provide information about the efforts of our volunteers. Our weekly “ENDANGERED!” column serves to inform you about the endangered plant and animal species found in and around these special natural areas, and how you can contribute to conservation efforts before it is too late.

Mitchell’s Satyr
By Yang Zhang

The first species featured in our “ENDANGERED!” column is the Mitchell’s satyr (pronounced say-ter), one of the world’s rarest butterflies. In Michigan, you may have the chance to spot this species, but without your help that opportunity may soon disappear.

Physical Appearance:

Mitchell’s satyr is a dark, chocolate brown, medium-sized butterfly with a wingspan that ranges from 1.5 to 1.75 inches. It has a three-part segmented body with a head, thorax and abdomen and antennae.

On the undersides of the butterfly’s rounded wings is a row of four to five orange-ringed, black circular eyespots with silvery centers. Beyond the eyespot rows on the outer part of the wing are two orange lines. The dorsal, or upper wing, is unmarked and thinly scaled. Males are slightly smaller and darker than females.

Preferred Habitat:
Mitchell’s satyr habitat is restricted to a unique type of wetland called a fen, which is a low-nutrient system that is enabled to support life with carbonate-rich ground water entering the system from seeps and springs. Fens are usually home to sedges, grasses and a wide variety of wildflowers, which makes the fen a magnet for insects including Mitchell’s satyr.

Some MNA sanctuaries, like the Butternut Creek Nature Sanctuary, are carefully managed to remain a fen and provide habitat for rare species such as the Mitchell’s satyr.

Life Cycle:
An adult Mitchell’s satyr lives for only a few weeks, but it takes a year for a caterpillar to turn into a mature butterfly.

The satyr goes through three life stages. In July, females lay tiny eggs on the young leaves of low, tender plants. The eggs hatch in 7-11 days. The caterpillars, which are very small and difficult to spot, feed on tussock sedge and other fine-leafed sedges. In winter, they hibernate under the snow and emerge in spring to resume eating until they form a chrysalis. The adult butterflies emerge from a cocoon in late June, and males emerge a few days earlier than females.

List Status:
Historically, Mitchell’s satyr inhabited fens across New Jersey, Ohio, Michigan, Indiana and possibly Maryland. Today, the butterfly can only be found in 19 fens in southern Michigan and northern Indiana.

The greatest threat to Mitchell’s satyr is habitat loss and degradation. Most fens have been altered or drained completely for urban and agricultural development. Pesticides, fertilizer and nutrient runoff from agriculture contaminate the fen wetlands, as well. In addition, wetland alteration has led to the invasion of exotic weeds, such as glossy buckthorn, which can shade out the satyr’s food plants. It’s also believed that butterfly collectors could have contributed to the population loss of the Mitchell’s satyr. Because there are so few butterflies, the collection of even a few individuals could harm the entire population.

Protection Efforts:
The U.S. Fish and Wildlife Service (FWS) added Mitchell’s satyr to the federal list of Endangered and Threatened Wildlife and Plants on June 25, 1991. It is illegal to harm, harass, collect or kill the butterfly without a permit from FWS.

FWS also created a recovery plan that describes actions needed to help the butterfly survive and thrive so that it can be taken off the endangered species list in the future.

Michigan and Indiana’s natural resource departments and partners have developed a Habitat Conservation Plan that provides a comprehensive framework for managing fens for Mitchell’s satyr.

The Michigan Department of Transportation, U.S. Fish and Wildlife Service, Michigan Department of Natural Resources and Environment, and The Nature Conservancy are jointly preserving and improving two of the butterfly’s habitats of Michigan: the Blue Creek Fen in Berrien County and the Paw Paw Prairie Fen in Van Buren County.

How You Can Help:
MNA protects close to 30 fens, two of which are home to the Mitchell’s satyr. Fens are managed in multiple ways. One way MNA manages fens is by holding prescribed burns. A fen in decent shape requires a prescribed burn every three-to-five years. Fens with a larger presence of woody growth or invasive species may require more frequent burns every two-to-four years. MNA also manually removes invasive species from fens and protects the hydrology of the land by objecting to potential developments in the area. With the help of MNA volunteers, we strive to protect the unique habitat of the Mitchell’s satyr.

MNA volunteers are currently working to protect this and other endangered species, and you can help too. Join our efforts as a volunteer removing invasive plants in the special natural areas where this species lives. Or, become a steward and take responsibility for planning efforts to maintain a specific MNA sanctuary. To find out how to get involved, visit our website.

Sources: U.S. Fish and Wildlife Service, Michigan Department of Natural Resources and Environment, Michigan State University

Beavers Disrupt Fen

by Hannah Ettema
MNA Intern

This past spring, it came to the attention of MNA that the new resident beavers of the Edwin and Margarita Palmer Memorial Sanctuary in Kalamazoo County were causing quite a problem. The sanctuary includes a prairie fen which is threatened due to the beavers. Prairie fens are rare plant communities declining across the landscape. Unlike pre-settlement times, southeast Michigan only has about 5,000 acres of prairie fen remaining today.

flooded fen

The flooded prairie fen

Fens are a type of wetland high in calcium and magnesium due to the fact that it is alkaline and fed by groundwater that picks up the elements via limestone. They are lower, however, in levels of nitrogen and phosphorus which leads to more evolved mechanisms in plants, such as the carnivorous sundew and pitcher plant which obtain their nutrients from insects. Fens are also botanically diverse due to presence of a wide array of microhabitats. For plant life to survive in fens, they require very specific water and nutrient levels which the beaver dam was disrupting.

Some but not all of the rare plants species that are under threat include the prairie Indian plantain, tussock sedge, purple fringe orchid, and sundew; all which have specific water requirements to flourish.

prairie indian plantain plant

The prairie indian plantain, photo Peter Gorman

The prairie indian plantain is not a particularly showy flower but its size is striking. With small flower heads and little noticeable scent, the plant is unique in shape and is an indicator of a high quality habitat. The plantain’s blooming period lasts about a month in early to mid summer and in the State of Michigan is listed as a species of special concern, which doesn’t grant them legal protection, it is carefully monitored because of its declining population in the state.

Tussock Sedge plant

Tussock sedge, photo Matt Schultz

Tussock sedge is a grass like plant that grows at or above water level. A good example of a microhabitat, the sedge’s hummock base acts as a wetland but the top of the hummock is more upland, leading different plants to grow at different places within each hummock. Typically growing in clumps of two feet by two feet, the sedge is a food source for a variety of animals including ducks, turkeys, deer, and our resident beavers. The sedge is also a great nesting site for birds.

purple fringed orchid plant

Purple fringed orchid

The purple fringed orchid is a tall one to two foot orchid blooming in July and August. The orchid is attractive to bees, butterflies, and birds and can grow anywhere from six to eighteen inches tall.

sundew plant

Sundew. photo John V. Freudenstein

The sundew plant is carnivorous. That alone should make it worth saving. On its leaves, a gel like substance is on the end of tendrils, appearing like morning dew all day long. In the sun especially, the glistening gel draws in insects for the plant to eat.  Sundew is also listed in the state of Michigan as a special concern.

beaver dam

The Beaver Dam, photo Matt Schultz

The beaver dam was blocking the drain of water from the prairie fen thus raising the water level to dangerous heights: 2 ½ to 3 feet above normal. For array of rare and unique plant species, including the ones listed above, an increase in water level could be detrimental.

MNA has many beaver dams in many properties around the state but none have ever caused such a severe problem to a habitat.

Initially, Andy Bacon, MNA Stewardship Coordinator and Matt Schultz, MNA Western Regional Stewardship Organizer, with the help of volunteers tried punching holes in the beaver dam to help drain the water from the flooding fen. However, within 2 days, each hole was plugged by the beaver because “they don’t have anything else better to do,” said Andy. More drastic measures needed to be taken to protect the prairie fen and its inhabitants.

Matt and Andy then worked to construct a beaver pond leveler. With the leveler, water from the flooded area is drained through a hole-drilled PVC pipe and carried through the beaver dam and out to the draining area. Around the hole-drilled end is a wire cage to block debris such as leaves and twigs from blocking the individual holes which drains the water.

Beaver Pond Leveler diagram

Beaver Pond Leveler

men working on leveler

Matt and Andy constructing the leveler, photo Matt Schultz

man with leveler in canoe

Andy about to canoe the leveler to the dam, photo Matt Schultz

On the day of installation this past August, Matt and Andy with the help of MNA volunteer steward Charles Goodrich canoed the leveler to the fen in pieces up the creek and to the flooded fen where it was constructed and installed past the beaver dam.

In order to fool the beavers, in addition to punching the necessary hole for the leveler, the guys also punched two additional holes in the dam so the beavers would repair the ‘fake’ holes and not the one being used by the PVC pipe.

Initially, the leveler was believed to have been a success by lowering the water level back to the it’s original state before the beavers arrived. However, after some time in the environment the water level is now 6 to 12 inches above the original level again.

beaver pond leveler in water

Where the leveler currently sits, photo Matt Schultz

Some steps are being taken to investigate and solve the water level problem. Schultz believes that the mesh cage of the leveler may be sticking too high out of the water causing the entire leveler to not drain properly. One idea is to push or sink the leveler further into the water for better drainage of the flooded fen.

Overall progress has been made. When the beavers leave and abandon their dam in the future, the leveler will be removed.

MNA would like to thank their members for making projects such as these possible to save such valuable sites such as the prairie fen in Edwin and Margarita Palmer Memorial Sanctuary.