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There’s Snakes in Them Thar’ Hills


Mon, Jun 12th, 2000
Posted in

Monday, May 29, 2000

With records for at least 39 of Minnesota’s 50 or so native amphibians and reptiles, the rugged stream-dissected Blufflands of the far southeastern corner of Minnesota is easily the most herpetologically diverse region of the state. For those unfamiliar with such things, herpetology (a name derived from the Latin root word herpeton which loosely translates as crawling thing) is simply the study of reptiles and amphibians in the technical terminology so prevalent throughout the realms of science.

In any case, there is little reason to be surprised by the diversity of reptile and amphibian species found in Minnesota’s southeastern corner, as the region is most certainly both geologically and ecologically unique. Collectively known as the “Driftless Area” and encompassing much or all of Goodhue, Fillmore, Houston, Olmsted, Wabasha and Winona Counties as well as adjacent portions of Wisconsin and Iowa, southeastern Minnesota is one of only two (the other located in the state’s extreme southwestern corner) narrow slivers of the state to have escaped the glaciations of our planet’s Ice Age.

Geologically this has preserved an isolated plateau of ancient sedimentary rock literally scraped from the landscape elsewhere in Minnesota by the relentless, repeated advance and retreat of mountainous, all encompassing ice sheets. Composed largely of limestone, sandstones and shale deposited by a long vanished sea, this rock often likewise preserves the fossilized remains of a wide variety of aquatic, 350 to 450 million year old, “Paleozoic” (literally “Early Life”) life-forms. Fossils of many of these organisms including the clam-like Brachiopods, Crinoids (Starfish relatives), Snails, and Cephalopods (basically squids enclosed by cone-shaped or coiled shells) are, in fact, often found in almost ridiculous abundance throughout much of the Blufflands.

Free of ice, regions like the Driftless Area probably further functioned as “refugia,” sanctuaries of a sort for a wide variety of animals and plants that would otherwise have been pushed far into North America’s more southerly portions. These reproductively isolated, refugee plant and animal populations in turn perhaps serving as the seeding stock in the re-colonization of land newly exposed as glaciers retreated.

Although spared the inevitable grinding force generated by a moving wall of ice hundreds of feet thick, the Driftless Area could not escape the power of the glacier completely unscathed. As ice fields receded, a gigantic lake of pooled melt water known as Glacial Lake Agassiz was left behind covering a sizable chunk of northwestern Minnesota as well as much of adjoining Canada. Eventually breaching the possibly frozen mud banks restraining it, Glacial Lake Agassiz unleashed a torrent of floodwater, which scoured out and cut the limestone valleys of Bluffland rivers and streams including the massive drainage basin affectionately called the mighty Mississippi.

In a manner vaguely similar to refugia, the valleys and basins of Bluffland waterways also possibly serve as “avenues of dispersal,” wildlife corridors which allow an assortment of species to immigrate into at least seasonally ice-free lands. This, in combination with the other previously mentioned events of the region’s comparatively recent geologic past, have created a topographically rich mosaic of diverse yet interconnected habitat types which are home to an equally diverse assortment of animals and plants.

The fairly extensive mixed deciduous woodlands dominated by maples, basswood and oaks which historically occupied much of the eastern portions of the Driftless Area, for example, is nevertheless liberally interspersed with scattered but sizable pockets of remnant upland prairie plant and animal communities. Floodplain forest, marshes and other wetland habitats typically associated with rivers and streams likewise abound, providing homes for yet another assemblage of different wildlife species. To the west, Bur and Pin Oak dominated woodlands and other assorted brush land and prairie openings contribute to overall ecological diversity as well.

As might be expected, a fairly substantial number of Driftless Area plant and animal species do not naturally occur elsewhere in Minnesota. These include trees such as the Black Walnut, orchids, various additional plants, insects, and assorted other animal species. Amphibians and reptiles are well represented among these “peripheral”
species as well with several snakes, turtles, frogs and a lizard included among the organisms found nowhere else in the state. At least two and possibly three species of Map Turtle as well as the Common Musk Turtle (known to occur in adjoining Iowa and Wisconsin but as yet unrecorded in Minnesota), for example, are exclusively confined to those portions of the Mississippi River bordering Minnesota’s Bluffland Counties.

The Upper Mississippi River Valley as well as the limestone bluffs of the Mississippi basin and other area waterways are likewise apparently vital to the survival of the Timber Rattlesnake and Black Rat Snake, two species that reach the northwestern most limits of their respective geographic distributions in southeastern Minnesota. A third snake species, the diminutive Massasauga or Swamp Rattler (like the Musk Turtle undiscovered in Minnesota but found in Wisconsin and Iowa), possibly occurs in the region as well.

Other distinctly southeastern Minnesota amphibians and reptiles include the Bullfrog (again naturally occurring only near the Mississippi and associated rivers, streams and wetlands), Pickerel Frog (which breeds in seasonally flowing Bluffland streams) and the Six-lined Racerunner, a small lizard that inhabits sand dunes, bluff prairies and other sandy Bluffland habitats.

While all the reptiles and amphibians of the Driftless Area are certainly worthy topics of discussion in and of themselves, such dialogue obviously must be postponed until some future date. Until then, however, please remember that there are snakes (not to mention other amphibians and reptiles) in them there hills! See ya - JPL

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