Fence line ecology: animal use of fence crossings in Southwestern rangelands

Authors: ZOROMSKI, LISA - Texas A&M University; DEYOUNG, RANDY - Texas A&M University; Goolsby, John; FOLEY, AARON - Texas A&M University; ORTEGA, J. ALFONSO - Texas A&M University; HEWITT, DAVID - Texas A&M University; CAMPBELL, TYLER - East Foundation

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2022
Publication Date: 10/1/2022
Citation: Zoromski, L.D., Deyoung, R.W., Goolsby, J., Foley, A., Ortega, J.S., Hewitt, D., Campbell, T. 2022. Fence line ecology: animal use of fence crossings in Southwestern rangelands. Ecology and Evolution. https://doi.org/10.1002/ece3.9376.
DOI: https://doi.org/10.1002/ece3.9376

Interpretive Summary: Nilgai antelope are implicated in the long-range movement of southern cattle fever ticks, Rhipicephalus microplus, in the environment, especially in Cameron and Willacy Counties in South Texas. Treatment methods for nilgai are needed to support the Cattle Fever Tick Eradication Program. Remotely activated sprayers developed for application of entomopathogenic nematodes at locations where nilgai congregate, especially at fence crossings where they move between pastures. Crossing locations are characterized by a depression of bare soil under the fencing created by repeated usage, and net-wire fences often have bottom wires that are broken or bent. The usage and crossing rates of fence crossings are poorly understood. We monitored 20 fence crossings on net-wire livestock fencing at 2 study sites on rangelands in South Texas, USA, during April 2018–March 2019. We assessed characteristics of fence-crossing sites and quantified crossing rates. We documented 10,889 attempted crossing events, 15 species of medium- and large-size mammals. Nilgai were the most common animal to cross with 1240 attempts and 330 successful crossings at the 20 monitored crossings. This information will be used to maximize the deployment and efficiency of the remotely operated sprayers used for eradication of cattle fever ticks on nilgai.

Technical Abstract: Fences are common throughout the world in both urban and rural landscapes. Surprisingly, there is limited knowledge of how wildlife react to fences, especially fences erected to contain livestock or mark property boundaries. Previous research on the effects of fencing on wildlife focused on large game mammals or long-distance migrators. Many other species of wildlife are affected by fencing, and often cross fences at defined crossing locations because they prefer to go underneath rather than over fences. Crossing locations are characterized by a depression of bare soil under the fencing created by repeated usage, and net-wire fences often have bottom wires that are broken or bent. The usage, placement, characteristics, and passage rates of fence crossings are poorly understood. We monitored 20 fence crossings on net-wire livestock fencing at 2 study sites on rangelands in South Texas, USA, during April 2018–March 2019. We assessed characteristics of fence-crossing sites and quantified crossing rates. We documented 10,889 attempted crossing events, with 58% (n = 6,271) successful. Overall, 15 species of medium- and large-size mammals and turkey (Meleagris gallopavo) contributed to crossing events. The average crossing location received 3–4 crossing attempts per day, but attempts varied by location and condition of the fence; larger crossings had higher crossing rates. Peaks in crossing activity corresponded with typical peaks of a species’ daily and seasonal movements and activity. Density and size of fence crossings were dependent on fence maintenance and not associated with vegetation communities or habitat variables. However, crossing locations were often re-established in the same locations after fence repairs. This is one of the first and most extensive studies on the effects of fences on animals in the southwestern rangelands. Our results will help land managers understand the impact of net-wire livestock fencing on animal movement, with implications for animal access to resources, management of impacted species, and disease management.