Introduction
Reptiles and amphibians have been recognised as being some of the world’s most at-risk species from the impacts of human development. In fact, 15% of reptilian species have been identified as threatened (classified as IUCN categories Vulnerable, Endangered or Critically Endangered), although due to lack of available data the true percentage is likely closer to 19% (Böhm et al, 2013). Amphibians are experiencing the worst global declines of all vertebrates with 32.5% identified as threatened, while 43.2% are experiencing population decreases (Stuart et al, 2004). Human-induced habitat loss and associated fragmentation of habitats has been identified as one of the primary causes of the global decline in populations of herpetofauna (Teixido et al, 2021).
One form of development causing both direct habitat loss and significant fragmentation due to their linear nature are roads. With an estimated 3.0 to 4.7 million km additional road length planned to be built across the world by 2050 (Meijer, J. et al. , 2018), herpetofauna are at an increased risk due to habitat loss, fragmentation and road mortality. Among studies that have recorded road mortality for all vertebrate groups, amphibians and reptiles often have the highest rates of mortality (Andrews et al., 2015; Baxter-Gilbert et al., 2015). In a review of thirteen studies, herpetofauna accounted for over 90% of roadkill in four studies and over 50% in eight studies (Colino-Rabanal and Lizana, 2012), and they have been recognised as being particularly vulnerable to the impacts of roads (Colino-Rabanal and Lizana., 2012; Paterson et al., 2019).
Roads can have further impacts on these species through changes to animal behavior, physical or chemical alteration of their natural environment and by non-native species dispersal (Van der Ree, et al., 2011; Colino-Rabanal and Lizana, 2012). Both reptiles and amphibians have low rates of movement compared to other species groups and each group can be specifically impacted by roads due to their ecology (Andrews and Whitefield Gibbons, 2005; Beaudry et al., 2008; Colino-Rabanal and Lizana, 2012). Reptiles also rely on thermoregulation and the surface heat from roads can attract individuals. Many amphibian species have complex life cycles with seasonal migrations that can be directly impacted by road mortality (Bouchard et al., 2009; Colino-Rabanal and Lizana, 2012). Amphibians are further vulnerable from roads due to their permeable skin which makes them even more sensitive to the secondary effects of road pollution (Colino-Rabanal and Lizana, 2012; Brady et al., 2022; Szeligowski et al., 2022).
Despite these significant impacts, public awareness and implementation of mitigation is lacking. Public perception of roadkill generally relates to size, and small species such as reptiles and amphibians tend to be given less attention (Colino-Rabanal and Lizana, 2012). Further, the topic of wildlife vehicle collision (WVC) studies, which influence mitigation, is biased towards certain groups of species. In a review, Taylor and Goldingay (2010) found 53% of WVC studies on wildlife studies focused on mammals, compared to only 9% on amphibians and 8% on reptiles. The focus on mammals is likely due to the higher human costs, as WVCs with large mammals result in high medical and vehicle-repair costs (Taylor and Goldingay, 2010). Cost-benefit analysis often forms part of reports for transportation authorities in relation to mitigation for WVCs.
Road mitigation strategies are most often implemented by transportation agencies rather than wildlife agencies, which results in a focus on motorist safety concerns over conservation (Lee et al., 2023). Where road mitigation focuses on species conservation instead, these are most often found along roads in protected areas rather than the wider road network (Lee et al., 2023). Based on their analysis, Lee et al. (2023) found that these contrasting perspectives result in a misalignment in priorities for certain species. Government funding for species protection and recovery has also been found to be highly disproportionate among species groups (Gerber,2016).
One key tool used to reduce WVC’s is wildlife fencing and it has been shown to reduce WVC by up to 80% (Clevenger, et al 2001) and can help to retain habitat connectivity when used in conjunction with wildlife crossings. However, there is also a significant lack of guidance across the world outlining the best approach to take when designing, implementing and maintaining mitigation fencing for reptiles and amphibians. Few biologists, planners and engineers have access to best practice guidance and those that don’t, have the freedom to implement unproven solutions. This raises the concern that inappropriate measures may be being used to manage conflict for these vulnerable species. Guidance is also vague and doesn’t often provide more details than some recommended materials and measurements to install above and below ground.
While road and transportation mitigation are the primary conflicts and applications for herpetofauna fencing, it has been used for a number of other reasons including: species protection, construction site exclusion, conservation monitoring, pest control, and for the safety of people. Fencing is often made out of a variety of materials including metal, thin plastics such as polyethylene and historically, tarpaper (Dodd, 1991). Recent studies have compared how animals interact with different fence materials and how material opacity impacts the speed in which animals travel along fences (Brehme et al., 2021; Milburn-Rodríguez et al., 2016). Brehme et al., (2021) found that herpetofauna tried to traverse transparent and semi-transparent fencing materials during summer trails in 2018 and 2019. This also caused them to move more slowly along the barrier and highlights the importance of how fence material impacts animal behavior.
In this article we will review current freely available best practice guidance for fencing designed to manage conflict of herpetofauna around transport networks from across the world. Upon reviewing this guidance we will compare and highlight key factors that include the following: o   Material type
o   Fence height
o   Fence features
We will then provide a summary of recommendations along with diagrams and descriptions that reflect the analyzed guidance from all the documents we review. We will also identify and highlight any areas that may need further research and investigation to help build upon the status quo and enable us to better utilize fencing as a conflict management tool for herpetofauna.