United States Department of Transportation
i
Testing ‘Wildlife Friendly’ Fence Modifications to Manage Wildlife and Livestock Movements
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2020-09-01
[PDF-5.23 MB]
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Edition:Final 09/2018 – 06/2020
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Abstract:Fences are ubiquitous across the landscape, yet there is little understanding on their effects on wildlife. Fences pose both indirect (i.e., access to habitat, energetic costs) and direct (i.e., mortality) consequences to wildlife, and so their effects are an important consideration. Wildlife managers, land managers, and Departments’ of Transportation, must explore mitigation options to allow for wildlife connectivity while addressing human concerns (i.e., keeping motorists safe). Fences along roadways serve as safety measures to protect humans from vehicular collisions with wildlife and livestock (i.e., all cattle) by containing animals in appropriate pastures and keeping them off roadways. Our objectives were to test wildlife friendly fence design that allows for daily and seasonal wildlife movements, while simultaneously keeping livestock in desired pastures. From 2012-2016, we tested three various bottom wire modifications to allow for safe wildlife passage which included smooth wire, clip/carabiners of the bottom two wires together, and PVC pipe on the bottom wire. From 2016-2018, we tested two additional fence modifications which were sage-grouse reflectors and PVC pipe on top wires to measure effects to ungulate crossing success from these modifications. Results from field trials indicate the use of either smooth wire or carabineers as a method to clip together the bottom two wires to a height of approximately 18 inches off the ground were two effective modifications at allowing passage by pronghorn, while the commonly proposed goat-bar (i.e., PVC pipe on bottom wire) was ineffective and created a negative behavioral response by pronghorn. In addition, the use of sage-grouse reflectors and PVC pipe on top wires had no substantial unintended consequences on the crossing behavior of pronghorn, mule deer or white-tailed deer, ultimately leading to a plausible multi-species wildlife friendly fence design and providing that the overall height of the fence as comparable/equivalent to adjacent fence lines. Our secondary objective was to test the influence of fence density around highways on species movement and connectivity in conjuncture with maintenance road mortality data through the Hi-Line region of Montana. Our connectivity modeling with highway mortality data show that fences East of Havre, MT are acting as barriers to seasonal migration for pronghorn and individuals are moving to the West of Havre, MT to cross in the fall and spring, but not winter, which indicates that increased fence densities may act as an ecological trap to individuals forced to move through sub-optimal habitat. In addition, we observed increased mortalities for mule deer with higher fence densities during fall and winter. Finally, through local, regional and national presentations, it is our intent to communicate our results to wildlife and habitat managers, as well as private landowners so as to consider these cost effective and prudent recommendations for on-the-ground implementation.
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