Evaluating Exclusion Barriers for Treefrogs in Agricultural Landscapes

Abstract

Agricultural co‐management aims to promote environmental sustainability while maintaining food‐safety standards. Amphibians, especially treefrogs, are known to enter fields of fresh produce intended for human consumption, which raises concerns for food safety and quality. We evaluated the effects of modifications to reduce the scalability of exclusion barriers on the fence‐crossing behavior of Pacific treefrogs (Hyliola regilla) from lettuce fields in the Salinas Valley of California during January to May 2019. From small‐scale field experiments, we found that fences modified with a horizontal lip at the top prevented all treefrogs from successfully crossing over. Fences incorporating sandpaper were also effective at deterring treefrog crossings compared to fences made of fiberglass square mesh (window screen) and polypropylene fabric (silt fence). The fence design that inhibited the most treefrog crossings—aluminum flashing with a horizontal lip—was a modification to commercially available material that is feasible to install at large scales, is durable over long periods of time, and can help to exclude additional nuisance wildlife, such as small mammals and lizards. Our findings provide quantitative evidence on the efficacy of an exclusion barrier constructed with off‐the‐shelf material that can be easily modified to improve the co‐management of amphibians and agriculture. © 2021 The Authors. Wildlife Society Bulletin published by Wiley Periodicals LLC on behalf of The Wildlife Society.

Learning from past designs: improving amphibian fences using an adaptive management approach

“…The materials used to create amphibian fences, including metal flashing, metal mesh, plastic sheeting and woven material are all readily available at hardware stores. Fences made of metal sheeting have been favoured for longer-term studies due to their durability and minimal maintenance (Hughes et al 2021). However, they are likely the most expensive option and prevent wind and water passage, which makes them more vulnerable to weather damage.…”

“…A lip of additional fence material should be included at the top of the fenceline irrespective of fence design, given how effective this is at limiting amphibian crossovers (Hughes et al 2021). Typically, a strip of non-supported, hanging material is the simplest design, either a single lip for 'I' shaped fences or two lips facing outward for 'V' shaped fences, and weighted along the end seam to minimise movement during strong winds.…”

“…Fences have been used for monitoring amphibian populations (Schlupp and Podloucky 1994;Allaback and Laabs 2002), as well as to confine them to protected areas (Schlupp and Podloucky 1994;Homyack and Giuliano 2002), create exclusion zones (Hughes et al 2021), and to manage invasive species such as the cane toad (Rhinella marina) (Florance et al 2011). Yet, unwanted movement of target amphibians under, over, or through fences is a common issue (Dodd et al 2004).…”

“…There is currently limited information on the most effective fence designs for amphibians (Arntzen et al 1995;Woltz et al 2008) and limited studies on aspects of fences that enhance their effectiveness (Dodd 1991;Hughes et al 2021). Thus, there is the potential for future programs to repeatedly suffer the same flaws that could be costly and cause harm.…”

On the fence: reevaluating the use of temporary amphibian exclusion fencing

“…The creation of “frog proof” fencing, both temporary and permanent, is now a global industry, with companies that cater to this market. However, there remains a lack of guidance on effective design, installation, and maintenance of amphibian fencing (Hughes et al 2021; Conan et al 2023) or comparisons with non‐fencing strategies.…”