Research Abstract

- The Effectiveness of Two Wildlife Barriers in Keeping Animals from Approaching a Highway -

Michelle Grasek , Dr. Tom Langen
Department of Biology
Introduction:
Roadside mortality has been identified as a cause of population decline in reptiles and amphibians, including turtles and frogs (Trombulak and Frissell, 2000).  Turtles are attracted to roadsides for several reasons, such as seasonal migration and breeding.  Areas of high herpetofaunal travel over roadways can be predicted based on the proximity of the roads to marshes on both sides (Langen et al in revision).  Mortality hotspots are predicted in areas with marshes within 100 meters on both sides of the road.  Causeways appear to be ideal sites for constructing barriers to keep the animals from crossing (as they are most likely to cross in these areas) and thus from getting run over (Langen and Johnson, unpublished manuscript).  In an attempt to keep herpetofauna off the roads, barriers have been constructed in several states (for example, Florida and New York) along the roadsides at mortality hotspots.   These barriers have been shown to be successful to some degree in reducing the numbers of reptiles and amphibians killed on roads (Trombulak and Frissell, 2000)  While research on the effectiveness of road barriers does exist, it is scarce, and there is even less comparative research on the effectiveness of various types of barriers. 
            Research on which types of road barriers are most effective in keeping various types of herpetofauna off the roads would make barriers more reliable and cost effective, in turn encouraging the construction of barriers at other predictable hotspots around the country. 
            A barrier was constructed on both sides of New York State Highway 68 at Upper and Lower Lakes State Wildlife Management Area, Saint Lawrence County, New York State by the New York State Department of Transportation, (NYSDOT) in cooperation with the New York State Department of Conservation (NYSDEC) and Clarkson University.  This barrier is made of two types of fencing: a wire-based version and a wood-based version.  The wire fencing is made of two types of wire fence: a large-gauge wire (openings of 4.875” x 1.75”), and a smaller gauge wire (openings 0.25” x 0.25”).  The fence is secured into the ground with recycled metal guardrail posts and the two gauges of fencing are secured together (smaller gauge covering the bottom half of the larger gauge wire) with cable ties.  This fence is set into the ground several inches for stability.  Its height above the ground is approximately 21.5”. 
The original wooden barrier is made of three slats of wood (0.75” x 7.75” x 92.5” each) set on each other with 1” gaps between each slats.  This fence was also buried several inches into the ground and its height above ground is approximately 17”. The same small gauge wire fencing from the wire barrier was used on the wooden fence.  This was staple gunned to the inside of the wood barrier, to cover the gaps between slats.
The objectives of this study include determining which of these two types of barrier are most effective in preventing reptiles and amphibians from approaching the highway.  The wooden fence is expected to be most successful because its height provides fewer opportunities for animals to escape; the top half of the large gauge wire is not covered with the smaller gauge wire, therefore presenting a possible escape route for small reptiles and amphibians if they are able to climb the small gauge wire.
 
Methods:
The corrals are roughly rectangular in shape and are attached to the barrier, which acts as the western wall in each type of corral.  The wooden corral (92.5” x 124.75” x 92.5” x 124.75”) uses as section of the wooden barrier as its western wall, and the other three walls are made of the same materials as this wooden barrier (wooden slats and small gauge wire of the same measurements, buried several inches into the ground).  The wire barrier (89.5” x 157” x 94” x 157”) uses a section of wire barrier as its western wall, and uses the same materials with the same dimensions as the wire barrier.  A mixed corral was also constructed early in the study, with the wooden barrier as its western wall and the other three walls based on the wire barrier.  This fence was removed and replaced with the wooden fence (previously described) because it did not represent the wooden barrier well enough.  For both the wire and wooden corrals, the small gauge wire fencing was attached to the outside of the corrals because the animals were utilizing it to cling to in order to escape the mixed fence.  In many cases, making the corrals identically reflect the barriers is impossible to ensure, although all efforts are taken to reduce error in this area, due to lack of similar equipment used by the NYSDOT in constructing the barrier
In our study we evaluated effectiveness of two types of barriers. The animals were put into the corrals for one hour at a time and their behavior was monitored and recorded every 5 minutes.  Escape methods (when escape occurred) were recorded and pictures taken when possible.  The herpetofauna in the study include 4 species of turtles, 3 species of frogs, and 1 species of snake.  

Results and Discussion:
Thus far in the study, a total of 18 tests have been run with Chelydra serpentina (snapping turtles), 9 for Chrysemys picta (painted turtles), 9 for frogs, and 6 for snakes.  Overall, 4 escapes have been recorded among C. serpentina, none for C. picta, 7 for frogs, and three for snakes.  One subject, C. serpentina, exhibited the ability to escape from the wooden and wire corrals, and two C. serpentina were able to escape from the mixed-type corral.  In all cases of escape, the turtles climbed vertically up the fences using the small gauge wire fencing to cling to with their claws.  Frogs escape with ease from both the wire and mixed corrals.  Frogs typically jump onto and cling to the small gauge wire fencing, climb to the top of it, and then jump out through the larger fencing.  More testing needs to be done with frogs in the wooden corrals.  Snakes escape easily over the wire corrals, but have not been found to escape from the wooden corrals. 
Several modifications are suggested based on the data and on behavioral observations.  Overall, the wooden fence model is recommended over the wire model.  For frogs and snakes in the wire corrals, the fence was only as high as the small mesh fencing because they can fit through the larger gauge fence.  This makes the height of the wire barrier approximately 10”, compared to 17” for the wooden barrier.  In addition, the mesh fencing should be placed on the outside of the corrals, to prevent the animals from clinging to it.  In the case of the wire fence, at least one turtle exhibited the ability to cling to the mesh fencing even when the fence was on the outside of the corral.  Also, it is suggested that the top portion of both types of fencing be angled inward, toward the animal habitat and away from the road, to prevent scaling of the fence by turtles and to help dissuade frogs and snakes from easily climbing up and over the fences. 

Works Cited:

Aresco, Matthew. Mitigation Measures to Reduce Highway Mortaility of Turtles and Other
            Herpteofauna at a North Florida Lake. Journal of Wildlife Management 69(2): 540-551;
            2005.

Langen, Dr. Thomas A., and Dr. Glenn Johnson.  Predicting Hotspots of Herpetofaunal Mortality
            on New York Highways: Validation of a GIS Model.  Unpublished manuscript. 

Langen, Dr. Thomas A.,  Journal of Wildlife Management in press.

Trombulak, Stephen C., and Christopher A. Frissell, 2000.  Review of Ecological Effects of
            Roads on Terrestrial and Aquatic Communities.  Conservation Biology, 14:1, p. 18-33.

This abstract provides a broad overview of the research - if you'd like to know more, you can email me (gingersnap0008@yahoo.com) or check out Dr. Langen's webpage for some answers and his email address. Thanks for taking interest!