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.