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"The Great Wall of Weaver"


Fri, Jul 13th, 2001
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Monday, July 2, 2001

As if near record flooding along the Upper Mississippi was not enough already, mid and late Spring 2001 for the most part proves to be gloomy, cool and gray. With the exception of two or three consecutive sunny, unseasonably hot and humid days with temperatures in the low nineties, it is a seemingly endless season of week after week of cloudy, almost blustery, rain filled skies.

Naturally, such weather offers little to improve conditions at Weaver. No warming, moisture stealing sunshine to help shrink the sand prairie’s flood-swollen wetlands. Area ponds, potholes and marshes remain engorged - slowly stagnating pools of water so uncharacteristically deep, dark, and cold.

Unlike previous years, aquatic traps catch little other than bowfin, carp and bullheads. The scattered turtles that do occasionally turn-up, whether Painted, Blanding’s or Snapper, are apparently just those few malcontents unwilling to await more balmy weather. The comparative lack of turtle captures is discouraging to say the least, and dominates all our thoughts and conversations.

Perhaps the depressed temperatures have caused our quarry to just "shut down," not an uncommon occurrence amongst those organisms termed "cold-blooded." This does seem highly unlikely, however, since each of the three previously mentioned turtle species are frequently observed awake and freely moving about in the frigid water of still completely ice-encrusted lakes and ponds.

Cold water may instead be reducing the turtles desire to feed, or their now greatly expanded wetland homes might actually be providing a virtual smorgasbord of normally unavailable foods in quantities far exceeding their average daily dietary needs. Certainly our bait of cheap sardines, which so effectively attracted these animals just last year, now largely decomposes within perforated cups almost utterly ignored.

Of course it is possible, perhaps even probable, that we simply cannot get traps close enough to capture our turtles. Indeed, many of our radioed animals have steadfastly remained well within the boundaries of their traditional haunts no matter how far underwater. In any case, all our turtle trapping efforts go largely unrewarded.

With typical aquatic traps ineffective, our attention increasingly focuses on other means of capturing turtles. Water depth and clarity makes dip netting by hand almost impossible as well, leaving little alternative other than beginning construction of a "drift-fence," a capture technique frequently used in studies of amphibian, reptile and small mammal populations.

Drift-fence "technology" is relatively straightforward; simply erect a barrier that will intercept such animals as they move about on land. Intercepted animals, theoretically at least, then move laterally along this barrier or fence until encountering and hopefully entering a number of strategically placed funnel or pit-fall traps, which are then periodically checked and emptied by researchers. Although only rarely used to study turtles in the past, this capture technique nevertheless did prove highly effective throughout the latter portions of the 2000 Weaver Dunes Blanding’s Turtle Research Project.

The material of choice for constructing our drift-fence is nothing more than good old-fashioned chicken wire with the lower edge buried in the ground to a depth of about three or four inches and standing approximately fourteen to sixteen inches high. This creates a nearly invisible barrier that may be readily "molded" to fit the contour of the landscape, and which is supported and stabilized by wooden stakes spaced at three to four feet intervals. Pit-fall traps consist of small, water-filled plastic "kiddie" wading pools, topped with another inverted plastic pool of identical size with entry holes and the "bottom" removed to allow access to captured animals.

Not surprisingly, drift-fences function most effectively when placed in areas supporting large numbers of migrating animals. Luckily, well over two decades of research at Weaver has clearly established the precise locality of a number of the "migration corridors" most heavily utilized by the region’s resident Blanding’s Turtles, a fact which certainly helps eliminate any potential reservations regarding the placement of our drift-fence.

We do, however, face one major obstacle, namely the overall "length" of the Blanding’s Turtle migration corridors at Weaver. Migration corridors so extensive, in fact, that by the beginning of the first week in June we have installed over three thousand feet of fence and have yet to achieve anything even remotely resembling a complete blockade. To put this into a somewhat more tangible perspective, if stood on end this year’s drift-fence would easily be twice as tall as Chicago’s Sears Tower, reputedly the second tallest building in the world. Just for the record, the world’s tallest building, Petronas Towers of Kuala Lumpur, Malaysia, would likewise equal less than half the height of our drift-fence.

To insure the safety of all captured animals this drift-fence, the Great Wall of Weaver if you will, must be monitored continuously. Its half-mile length walked and its traps cleared a minimum of four to five times each and every day regardless of the weather. After that the real work can begin, the nightly data collection and processing of captured Blanding’s Turtles that must be returned bright and early next morning to continue on their journeys. Still I believe that when all is said and done, each of us working on the project, while tired and worn-out, will undoubtedly be smiling.
Until next time "Nuff Said" – JPL


John Levell

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