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Estimating the Percentage of Wildlife that Escape the Roadway Using Wildlife Exits Along State Highway 100 in South Texas

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  • Estimating the Percentage of Wildlife that Escape the Roadway Using Wildlife Exits Along State Highway 100 in South Texas
Zarina Sheikh, University of Texas Rio Grande Valley
Richard J. Kline, University of Texas Rio Grande Valley
Kevin Ryer, University of Texas Rio Grande Valley
John H. Young, Jr., Texas Department of Transportation
Mitigation / restoration
Technical Session 15: Good Fences Make Good Crossings

Wildlife movements to find resources, mates, and to defend territories are a key component of survival for many species. This need for movement often causes wildlife to cross heavily trafficked highways, resulting in road mortalities. To mitigate road mortality for the U.S. endangered ocelot in Cameron County, Texas, the Texas Department of Transportation (TxDOT) installed a series of wildlife crossings, gates, wildlife guards, and continuous fencing along an 11.9 km section of State Highway 100 between Los Fresnos and Laguna Vista, Texas. After construction, wildlife that continued to circumvent wildlife guards and areas of open fencing at access roads to enter the roadway were still being hit by vehicles. Due to concerns that this could also occur with ocelots, TxDOT installed ten wildlife exits (WE) in February 2019 in an effort to reduce wildlife road mortalities for species that cross onto the highway and need a safe option to exit the right-of-way (ROW). To document use, two cameras were installed at each of the ten exits; one on the roadside and one on the habitat side to capture activity for all bobcats, coyotes, jackrabbits, domestic cats, skunks, and opossums. Our objectives were to determine effectiveness and species usage, as well as to estimate the percentage of wildlife that are crossing back into the habitat using a WE. All six of our target species used a WE to travel from the ROW to the habitat. Although no ocelots were documented during this study, bobcats are often used as a surrogate species. Results of this study showed that 43% of bobcats and 6% of coyotes remaining on the road used a WE to get off the ROW and return to the habitat. However, each species also learned over time to use a WE to incorrectly access the ROW. For WE interactions specifically, 31% of bobcats and 25% of coyotes that crossed through a WE traveled from the habitat to the road. Based on these results, it is likely that WE would be used by ocelots to exit the roadway, but modifications such as one-way doors need to be investigated to prevent incorrect usage. Information on the effectiveness of these novel structures and characterization of areas used most often by target species will be useful in the development of future WE to optimize placement and usage of these structures.

road ecology
mitigation structures
wildlife exits
ocelots
wildlife conservation
south Texas

Header image courtesy of Martin Gradjean -- Air Traffic Network

ICOET 2025 — International Conference On Ecology and Transportation