Fall 2013

Prairie Butterflies in Trouble

By Robert Dana, Ph.D. MNDNR

The Scientific and Natural Areas Program protects a number of important native prairie sites where plants that once dominated almost a third of Minnesota continue to thrive amid the cropland that now commands their former domain. Visitors to these sites can obtain some idea of what our forebears, both Native American and immigrant, beheld when they ventured into the prairie landscape. The botanical richness of the prairie is immediately evident to a visitor today. Less so, but just as important, is the zoological richness and diversity of these prairie remnants. The largest, most conspicuous of the animals—bison and elk, bears and wolves—are gone, but the prairie comprised a wealth of smaller denizens that continue to inhabit the remnant patches. Of these, the arthropods are arguably the most important single group, especially the insects and the spiders and their relatives. The number of species is one measure of this, but more significant is the diversity of functional roles they play—pollination, seed scarification and dispersal, soil aeration, nutrient cycling—that is vital to the prairie ecosystem.

Unfortunately, it is difficult to assess how successful we have been in the conservation of the arthropod fauna of our prairie preserves. One group that is somewhat exceptional in this regard is the butterflies. These are relatively large and conspicuous, at least as adults, and there has been a substantial amount of interest in the group, resulting in the accumulation of more data than is typically available. If this group is indicative of how prairie insects in general are faring the outlook is disturbing. There are 12-15 butterfly species that are prairie specialists in Minnesota—occurring principally or exclusively in native prairie or savanna habitats. Four of these may no longer exist in Minnesota: Karner blue, Uhler's arctic, Uncas skipper and Poweshiek skipperling. The Minnesota occurrences of three of the four are on the edge of their respective ranges, but Minnesota constitutes a major part of the range of the Poweshiek skipperling. Most alarming, it has disappeared from most of its range beyond Minnesota as well, including the eastern Dakotas and northern Iowa. This little butterfly was until recently the most commonly encountered of the prairie-specialist butterflies in Minnesota, almost as reliably present in prairie remnants as leadplant or blazing stars.

The Poweshiek skipperling belongs to a group of butterflies frequently referred to as grass skippers—the larval stages of these species feed only on grasses or sedges. In addition to the Poweshiek skipperling and Uncas skipper, another seven of Minnesota's prairie-associated butterflies belong to this group. We lack recent data for three of the seven, the Dusted skipper, Assiniboia skipper and Garita skipperling, but for the four remaining species, the Arogos skipper, Dakota skipper, Ottoe skipper, and Leonard's skipper (shown above), recent survey efforts indicate significant declines. In the case of Leonard's skipper, the eastern Minnesota populations, in sand prairie and savanna habitats, do not appear to have declined recently, but the western populations, belonging to the distinctive subspecies known as the Pawnee skipper, have. The most troubling of these is the Dakota skipper, whose range is even more limited than that of the Poweshiek skipperling, with Minnesota being a similarly significant portion.

We do not know what the cause or causes of these declines might be. This should not be surprising—even with the millions spent on research, the explanation of colony collapse disorder in the economically important domestic honeybee remains elusive. There is considerable concern about the use of prescribed burning for prairie management. Small populations, restricted to small, isolated sites, are, on basic principles, vulnerable to elimination from a site by fire. The SNA program has addressed this concern by dividing sites into multiple burn units and rotating burns among them to allow for within-site survival and recolonization, but the adequacy of these risk-management practices is uncertain given our limited knowledge of the biology and behavior of these organisms. Insecticide drift is another possible factor; large acreages are sprayed for control of soybean aphid, which exploded in Minnesota beginning in 2001. Several different products are used for aphid control, all of which are highly toxic to butterflies and moths (and most other insects). These and other products are also applied to the other major crops in the state. We should begin monitoring prairie sites to determine whether dangerous levels of insecticide residues are present.

Protecting the insect life in SNAs will clearly be a daunting challenge. Visitors to prairie SNAs can help by familiarizing themselves with the butterflies mentioned in this article and watching for them when visiting. Submitting documentation with digital photography is relatively easy and can provide valuable information.

 

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SNA Events

Get up close and personal with buckthorn this fall. Help out on one or more volunteer projects to combat this aggressive invasive species on SNAs. A full list of projects and other SNA events is available on the SNA Events Calendar.

 

09/29/13	St. Croix Savanna SNA	Volunteer Project: Buckthorn Removal
10/26/13	Seminary Fen SNA	Volunteer Project: Clean-up and Buckthorn Removal
10/27/13	Wolsfeld Woods SNA	Volunteer Project: Buckthorn Pull

 

 

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Site Highlight: Hastings SNA

Within the City of Hastings an upland hardwood forest and a floodplain forest host a wide diversity of native plants. These habitats and associated rare species were the basis for the October 1974 designation of Hastings SNA, the third SNA to be created in Minnesota. Friends of the Mississippi River, an organization working to protect the Mississippi River watershed in the Twin Cities, coordinates with the SNA Program in management of this site.

A major street running though the SNA has been in need of repair. This spring work began on the road. In order to minimize damage to native plants along the roadway Friends of the Mississippi River worked with the SNA Program and the City of Hastings on a plan to rescue natives along the road right-of-way. Plants were dug up in mid-May of this year and cared for the summer in containers. On September 21st the rescued natives plants were replanted along the reconstructed road.

 

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Notes from Site Stewards

The number of site stewards monitoring SNAs across Minnesota has grown to over 100 this year. Their observations provide invaluable information to the SNA Program. Here are some interesting notes from reports:

• Site steward Ann Ihrke, working with her husband Brad Ihrke and SNA Naturalist Mike Dunker made a major safety improvement for visitors to Cherry Grove Blind Valley SNA on August 18th. The old barbed-wire fencing along the entire eastern boundary of the site was removed. Completed work is shown in the adjacent photo. This is the side of the site recommended for parking and access, so their work will remove a hazard to entry into the site. They also replaced and reset some boundary signs.
• Excitement and enthusiasm were in abundance at Iron Springs Bog SNA this summer. Even before new site steward Angela Shogren was officially enrolled on July 17th she had researched and visited the site to familiarize herself with it. She has since brought out others to help with plant identification, reported her first observations, and brainstormed ideas for stewardship with SNA staff.
• Many years of diligent work appear to be paying off at Clinton Prairie SNA. Site stewards Mike Perry and Ellen Fuge found very low numbers of invasive birdsfoot trefoil this summer—certainly the result of past eradication efforts.
• Illegal activity at Mille Lacs Moraine SNA highlights the importance of stewards and their regular observations. On a recent site visit stewards John and Marilyn Anderson found that the gate on the south side of site had been stolen. That's right, someone actually took the 12 feet wide and 50 inches high gate that likely weighed in at over 100 pounds. The Andersons reported the missing gate to the local Conservation Officer and SNA Staff, who are now investigating the offense. This is a great reminder that having regular site observations is critical for finding and addressing problems promptly.

Thanks stewards for submitting those reports!

 

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Nature Notes is the Minnesota Scientific and Natural Areas quarterly e-newsletter. It seeks to increase interest, understanding and support of natural areas while promoting involvement in the protection of these special places. Contact us at sna.dnr@state.mn.us.