On damp nights in the spring in temperate regions, amphibians emerge from their winter hideouts to migrate to their breeding pools. Nothing will stop their drive to reach water to spawn and so they brave a barrage of cars and artificial barriers along their route which often results in them getting squashed.
Amphibians have complex, biphasic life histories which makes their conservation challenging. Most species require high quality aquatic and terrestrial habitats which must both be connected by a transition habitat during migrations (Baldwin et al. 2006).
As urbanisation expands around the world, many aspects of wildlife physiology, movement patterns, population genetics and overall health are affected due to anthropogenic stressors such as habitat loss and artificial light pollution. The unprecedented expansion in transport infrastructure in the past century has had massive impacts on amphibian populations around the world (Beebee 2013, Glista et al. 2008). Roads fragment habitats and cause high mortality as well as being a significant source of chemical contaminants (Petrovan and Schmidt 2016, White et al. 2017, Bird et al. 2019).
Roads which bisect migratory routes severely restrict the dispersal of amphibians between their breeding areas and terrestrial habitat. This can have catastrophic impacts on gene flow and metapopulation dynamics potentially leading to population declines, genetic isolation and even extinction (Fahrig and Rytwinski 2009, Marsh and Trenham 2001). Therefore, mitigating road-kill and habitat fragmentation is a conservation priority (Puky 2005, Beebee 2013, Cushman 2005). Genetic bottlenecks as a result of fragmentation reduce the viability of populations and can leave amphibians more vulnerable to other synergistic environmental stressors such as climate change, pollution and emerging wildlife diseases (Cushman 2005, Laurence and Useche 2009). Urban fragmentation is known to decrease species diversity and abundance and coupled with wider habitat degradation such as edge effects and loss of breeding habitats, can make cities particularly challenging for amphibians (Bickford et al. 2011, Scheffers and Paszkowski 2012). At some field sites, mass mortality on roads can cause complete extirpation of anurans and salamanders within years (Cooke 2011, Hels and Buchwald 2000). With more and more cars on the roads, it is increasingly difficult for amphibians to avoid them.
Temperate amphibians such as the common toad have experienced significant and continuous declines. In the UK it is estimated that 20 tonnes of common toads (Bufo bufo) are killed annually as they migrate across roads to reach their breeding ponds, with up to 13,000 annual mortalities being recorded even at manned amphibian crossings. This has contributed to a 68% decline in their population size in the past 50 years at a rate of 2.26% per year. The severity of the population reduction means that these toads are no longer ‘common’ toads and could soon qualify as vulnerable on the IUCN Red List (Petrovan and Schmidt 2016).
The COVID-19 pandemic has caused immense human tragedy as it has spread around the world straining healthcare services and paralysing economic systems. Quarantine restrictions imposed by governments in order to slow the spread of the virus, have caused extraordinary disruption to our globalised society but have created rare opportunities for some wildlife species (Zellmer et al. 2020). As bustling metropolises slowed down they were occupied by usually elusive fauna; wild boars were seen roaming Barcelona’s quiet neighbourhoods, flamingos flocked to New Delhi’s lakes, river otters and puma stalked silent streets in Chile and sea turtles thrived on empty Brazilian beaches. A recent paper by Rutz et al. (2020) coined the term ‘anthropause’ for this rapid and unprecedented “global slowing down of modern human activities, notably travel.” It has resulted in profound short term environmental benefits such as improved air and water quality as well as reduced wildlife disturbance.
Research conducted during the Anthropause has highlighted both known and less known impacts that we are having on the natural world and is providing a unique opportunity to study wildlife populations during a time of reduced human presence all around the world (Forti et al. 2020, Zellmer et al. 2020, Bates et al. 2020). Monitoring the ways wildlife has responded to covid lockdowns in urban areas allows researchers to quantify the impacts human mobility is having on wildlife in the Anthropocene (the term given to our geological age, dominated by human activities) and potentially find strategies to mitigate biodiversity loss (Rutz et al. 2020, Stokstad 2020). This research provides invaluable insight into the mechanisms of human-wildlife interactions that will inform conservation for decades to come.
Lockdowns in spring and summer of 2020 meant fewer vehicles on the road which has significantly decreased road mortality for many species including amphibians. A “roadkill reprieve” this year may have made amphibian migratory journeys much safer according to Goldfarb (2020). A study by Grilo et al. (2020) calculated that 194 million birds and 29 million mammals are killed on European roads each year under normal circumstances while in Brazil, road mortality has superseded hunting to become the “leading cause of direct human caused mortality in terrestrial vertebrates” (Carvalho et al. 2014). This year they may not suffer the same fate. Simply driving less could have been “the biggest conservation action” taken by humanity over the past 50 years according to Fraser Shilling of the Road Ecology Centre at UC Davis and could have potentially saved the lives of 500 million vertebrates (Nguyen et al. 2020).
In March and April as traffic flows dipped by 73% across the US, many creatures received temporary respite from road collisions, with Californian mountain lion fatalities down 58% and a 48% decrease in roadkill deaths in Maine. Although much of the data focuses on large mammals, the same is true for smaller, less mobile animals such as amphibians, snakes and turtles (Katz 2020).
At amphibian crossings this spring in Maine, wood frogs, salamanders and newts were twice as likely to survive than in previous years, which is great news for these sensitive creatures that are very vulnerable to habitat fragmentation. Four amphibians successfully crossed the road for every one squashed this year, half as many as in previous years (Goldfarb 2020, Keim 2020).
A study by Manenti et al. (2020) examined the effects of the COVID-19 lockdown and reduced human disturbance on wildlife in Italy and describes both positive and negative effects on biodiversity conservation. As well as allowing wildlife to explore new habitats and extend their activity periods, species richness and reproductive success increased while roadkill diminished in temporarily quieter areas. Some negative ecological effects included reduced enforcement of regulations, and postponed conservation action such as invasive species management.
A decrease in road traffic led to significantly improved survival of migrating amphibians on Italian roads this spring at eight toad crossings. Data suggests that there was an 80-90% decrease in nocturnal road traffic at these study sites during the anthropause. Four hundred and eight common toads (Bufo bufo) and 16 agile frogs (Rana dalmatina) were recorded as roadkill in 2019, and this dropped to only 38 toads and zero agile frog mortalities in 2020. The median mortality of road killed amphibians at each site decreased from 53 individuals to only one in 2020 (with some sites recording no mortalities) indicating that an increased number of adults made it to their breeding pools this spring giving populations a much needed boost. Manenti et al. (2020) also surveyed transects in Liguria, Northern Italy to quantify the effects of reduced traffic on common wall lizards (Podarcis muralis) and Western green lizards (Lacerta bilineata) and found a similar 10-fold decrease in road mortality.
Many of the conservation benefits the Anthropause created are ephemeral, as traffic returned to baseline levels once economic activity restarted. Although breeding booms this spring may bring some respite to struggling populations, alone, they will not be able to counteract the extreme loss of genetic diversity as a result of population bottlenecks in the past.
The information collected over the Anthropause highlights the need to improve the landscape to make it safer for all wildlife and particularly amphibians (Merrow 2007). If we can alter our transport networks to counter the effects of large-scale urban development and increased transport infrastructure we could go some way to mitigating the catastrophic impact of habitat fragmentation. The observed benefits that limiting road traffic can provide for migrating amphibians could inform more decisions about temporary, focused road closures around the world in the future to replicate this effect and to better conserve endangered amphibian and reptile species (Manteni et al. 2020).
Building fauna tunnels and bridges across dangerous roads to link habitat fragments allows animals to cross safely (Dodd et al. 2004, Gonzalez-Gallina 2018, Vartan 2017). Road mortality decreases by up to 85%-95% with animals responding surprisingly quickly to the change as ecosystems are reconnected (Vartan 2019). Wildlife tunnel projects can mitigate the effects of fragmentation and have been shown to allow amphibians to move successfully between sites bisected by roads. Tunnels and drift fences reduce road mortality, promote habitat connectivity, and allow amphibians to colonise new ponds leading to population increases and expansion into reconnected habitat (Jarvis et al. 2019). These movement corridors also allow roads to be permeable to a host of other wildlife species like reptiles and small mammals (Purky 2005, Jarvis et al. 2019).
The incredible work done by volunteers at amphibian crossings who help migrating amphibians make it across roads (Petrovan and Schmidt 2016) could also contribute to sustaining population increases this spring from quieter road traffic.
COVID-19 has also highlighted how explicitly intertwined human and wildlife health are and the catastrophic impacts of the overexploitation of nature. Emerging wildlife diseases such as chytrid fungi and ranaviruses threaten amphibians around the world and their spread has been catalysed by anthropogenic trade in our globalised world (O’Hanlon et al. 2019). A slowdown in global trade and human flows as a result of COVID-19 could also have gone a way to mitigating the spread of the pathogens that imperil amphibians (Forti et al. 2020). Although this benefit may only be short-lived as economies restart, there is hope that better regulation of the wildlife trade, in order to decrease the chances that future novel zoonotic diseases spill over from wildlife reservoirs in the future, could benefit amphibians too. Since the wildlife trade is responsible for the translocation of many amphibian pathogens (Kolby et al. 2014, O’Hanlon et al. 2018) better regulation and enforcement of the trade in live animals could help stem the spread of emerging amphibian diseases and invasive species (Forti et al. 2020).
The Anthropause provides us with an excellent opportunity to reimagine our relationship with nature and our socio-economic systems so that biodiversity can flourish and acts as a reminder that biodiversity is essential for maintaining human health and wellbeing too.
The disruption to the economic status quo that the pandemic has created gives us a pivotal opportunity to consider a greener, more sustainable future where people and wildlife can thrive. In order to effectively stem biodiversity loss in the Anthropocene, we must use this pivotal moment to plan a green recovery which incorporates wildlife conservation into all economic rebound projects. In the UK this means not viewing the protection of great crested newts as a delay to construction (Howard 2020) but valuing them as integral parts of a plan to balance our economic and environmental ambitions. It is also a perfect opportunity to invest in road mitigation measures such as wildlife tunnels and fauna bridges to reduce the detrimental impact they can have on wildlife populations (Merrow 2007), with the added benefit of being excellent economic multipliers.
November 2020 Croaking Science article by Xavier Mahele
Bibliography
Baldwin RF, Calhoun AJK and Maynadier PG (2006) Conservation planning for amphibian species with complex habitat requirements: A case study using movements and habitat selection of the wood frog Rana sylvatica Journal of Herpetology 40 (4).
Bates AE, Primack RB, Moraga P and Duarte CM (2020). COVID-19 pandemic and associated lockdown as a “Global Human Confinement Experiment” to investigate biodiversity conservation Biological Conservation 248, 108665.
Beebee TJC (2013). Effects of road mortality and mitigation measures on amphibian populations. Conservation Biology 27(4).
Bickford D, Ng TH, Qie L, Kudavidanage EP and Bradshaw CJA (2010). Forest fragment and breeding habitat characteristics explain frog diversity and abundance in Singapore. Biotropica 42, 119-125.
Bird RJ, Paterson E, Downie JR and Mable BK (2018). Linking water quality with amphibian breeding and development: A case study comparing natural ponds and Sustainable Drainage Systems (SuDS) in East Kilbride, Scotland.The Glasgow Naturalist 27.
Carvalho NC de, Bordignon MO and Shapiro JT (2014). Fast and furious: a look at the death of animals on the highway MS-080, Southwestern Brazil Iheringia. Série Zoologia 104 (1).
Cooke A (2011). The role of road traffic in the near extinction of Common Toads (Bufo bufo) in Ramsey and Bury. Nature in Cambridgeshire 53, 45-50.
Cushman SA (2006). Effects of habitat loss and fragmentation on amphibians: A review and prospectus. Biological Conservation 128, 231-240.
Dodd C, Barichivich WJ and Smith LL (2004). Effectiveness of a barrier wall and culverts in reducing wildlife mortality on a heavily travelled highway in Florida. Biological Conservation 118, 619-631.
Fahrig L and Rytwinski T (2009). Effects of roads on animal abundance: an empirical review and synthesis. Ecology and Society 14(1): 21.
Forti LR, Japyassú HF, Bosch J and Szabo JK (2020). Ecological inheritance for a post COVID-19 world. Biodiversity and Conservation 29, 3491-3494.
Goldfarb B (2020). Lockdowns Could Be the ‘Biggest Conservation Action’ in a Century. The Atlantic.
González-Gallina A, Hidalgo-Mihart MG and Castelazo-Calva V (2018). Conservation implications for jaguars and other neotropical mammals using highway underpasses. PLOS ONE 13(11).
Hels T and Buchwald E (2001). The effect of road kills on amphibian populations. Biological Conservation 99, 331-340.
Howard J (2020). Boris ‘the Builder’ Johnson has found a new scapegoat: the humble newt. The Guardian 2/7/20.
Jarvis LE, Hartup M and Petrovan SO (2019). Road mitigation using tunnels and fences promotes site connectivity and population expansion for a protected amphibian. European Journal of Wildlife Research 65, 27.
Katz C (2020). Roadkill rates fall dramatically as lockdown keeps drivers at home. National Geographic 26/6/20.
Keim B (2020). With the World on Pause, Salamanders Own the Road: Traffic is down thanks to the pandemic. That’s good news for amphibians looking to migrate safely The New York Times
Kolby JE, Smith KM, Berger L, Karesh WB, Preston A, et al. (2014). First Evidence of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) and Ranavirus in Hong Kong Amphibian Trade. PLOS ONE 9(3).
Laurence WF and Useche DC (2009). Environmental Synergisms and Extinctions of Tropical Species. Conservation Biology 23,1427-1437.
Manenti R, Mori E, Canio VD, Mercurio S, Picone M, Caffi M, Brambilla M, Ficetola GF, Rubolini D (2020). The good, the bad and the ugly of COVID-19 lockdown effects on wildlife conservation: Insights from the first European locked down country. Biological Conservation 249, 108728.
Marsh DM and Trenham PC (2001). Metapopulation dynamics and amphibian conservation. Conservation Biology 15(1), 40-49.
Merrow J (2007). Effectiveness of amphibian mitigation measures along a new highway. UC Davis: Road Ecology Centre.
O’Hanlon SJ, Rieux A, Farrer RA, Rosa GM, Waldman B, Bataille A, Kosch TA, Murray KA, Brankovics B, Fumagalli M, Martin MD, Wales N, Alvarado-Rybak M, Bates KA, Berger L, Böll S, Brookes L, Clare F, Courtois EA, Cunningham AA, Doherty-Bone TM, Ghosh P, Gower DJ, Hintz WE, Höglund J, Jenkinson TS, Lin C-F, Laurila A, Loyau A, Martel A, Meurling S, Miaud C, Minting P, Pasmans F, Schmeller DS, Schmidt BR, Shelton JMG, Skerratt LF, Smith F, Soto-Azat C, Spagnoletti M, Tessa G, Toledo LF, Valenzuela-Sánchez A, Verster R, Vörös J, Webb RJ, Wierzbicki C, Wombwell E, Zamudio KR, Aanensen DM, James TY, Gilbert MTP, Weldon C, Bosch J, Balloux F, Garner TWJ, Fisher MC (2018). Recent Asian origin of chytrid fungi causing global amphibian declines. Science 360, 621-627.
Nguyen T, Saleh M, Kyaw M, Trujillo G, Bejarano M, Tapia K, Waetjen D Shilling F (2020). Road Special Report 4: Impact of COVID-19 Mitigation on Wildlife-Vehicle Conflict. Ecology Centre UC Davis.
Puky M (2005). Amphibian road kills: a global perspective. UC Davis: Road Ecology Centre UC Davis.
Rutz C, Loretto M, Bates AE et al. (2020). COVID-19 lockdown allows researchers to quantify the effects of human activity on wildlife. Nature Ecology and Evolution 4, 1156-1159.
Scheffers BR and Paszkowski CA (2012). The effects of urbanization on North American amphibian species: Identifying new directions for urban conservation. Urban Ecosystems 15(1).
Stokstad E (2020). Pandemic lockdown stirs up ecological research. Science 369, 893.
Vartan S (2019). How wildlife bridges over highways make animals—and people—safer. National Geographic 18/4/20.
White KL, Mayes WM and Petrovan SO (2017). Identifying pathways of exposure to highway pollutants in great crested newt (Triturus cristatus) road mitigation tunnels. Water and Environment Journal 31, 310-316.
Zellmer AJ, Wood EM, Surasinghe T, Putman BJ, Pauly GB, Magle SB, Lewis Js, Kay CAM, Fidino M (2020). What can we learn from wildlife sightings during the COVID-19 global shutdown? Ecosphere. 6:11(8), e03215.
