How do fences affect animal movement behavior?

Each year, Journal of Applied Ecology awards the Southwood Prize to the best paper in the journal by an author at the start of their career. In this post, Wenjing Xu discusses her shortlisted paper which examined the behavioural responses of two migratory ungulate species to linear barriers in Wyoming, USA.

Each year, thousands of migratory mule deer and pronghorn venture through the sagebrush plain in western Wyoming, USA, leaving their winter ranges to summer homes. However, to reach their destination, they must navigate more than 6,000 kilometers of fences – a length nearly twice of the U.S. – Mexico border.

Previously, researchers mostly considered fences as barriers that hinder animals from crossing. However, most fences are semi-permeable. For example. mule deer often jump over fences and pronghorn can crawl under them as long as they find a proper crossing spot. Hence, to examine fences’ effect on migratory animals, the question becomes “how do fences affect animal movement behavior as animals encounter fences?” 

Photo: Joe Riis

The answer to the question is – more than what we thought. To examine animals’ behavioral responses to fences, my colleagues and I developed a spatial- and temporal-explicit approach, Barrier Behavior Analysis (BaBA). BaBA is an openly availably R package and can classify animal movement trajectories near linear features into six different types of behaviors: Bounce, Trace, Back-and-forth, Trapped, Quick cross, and Average movement. The first four categories indicate altered movement behaviors that would not be exhibited if fences were absent. We found that an average pronghorn encounters fences about 248 times a year, nearly double the rate of an average mule deer. For both species, nearly 40% of fence encounters result in altered movement behaviors.

Photo: Wenjing Xu

Before this study, conservation groups have already sensed the potential impacts fences have on wide-ranging animals like pronghorn and mule deer. Many of them have initiated programs to modify fences into a more “wildlife-friendly” design.

A wildlife-friendly fence typically has a smooth bottom wire at least 18 in (46 cm) off the ground, so animals like pronghorn can go under. Yet, fence modification is expensive and prioritization has always been a challenge on the ground. Responding to this need, we showcased in our study how to aggregate the BaBA-generated behavioral information to pinpoint the most problematic fence segments across the landscape.

Photo: Wenjing Xu

The recent formalization of fence ecology as a subdiscipline has promoted substantial interest from scientists and managers to better understand fences and their ecological effects. Our study provides new evidence on the extensive effects of fencing on wide-ranging animal movement.

We hope BaBA can play a significant role in generating synoptic knowledge on the ecological effects of fences and other linear infrastructures across systems.

Read the full paper Barrier Behaviour Analysis (BaBA) reveals extensive effects of fencing on wide-ranging ungulates in Journal of Applied Ecology.

Wenjing Xu

Wenjing Xu is a Ph.D. student at the University of California, Berkeley. She is broadly interested in terrestrial movement ecology in arid and semi-arid ecosystems. Her dissertation research focuses on fences and their effects on ungulate movement behavior, space use, and demographic outcomes in the Greater Yellowstone Ecosystem. In her upcoming postdoctoral stage, she hopes to better understand wildlife-livestock coexistence in pastoral rangelands from the perspective of ecosystem function. Wenjing obtained an M.S. degree in geospatial science at the University of Georgia, and a B.S. degree in natural resources at the China University of Geosciences. The paper published in the Journal of Applied Ecology is one of her dissertation chapters, and she is thankful for the support and advice from all her coauthors and lab mates.

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