Roads and Amphibians: An Issue in Conservation and Policy

By: Jacob Balcanoff, Stephanie Brown, and Amanda May

The Problem

Our road system is paved in a legacy of conflict between engineering and the environment. Humans have always sought ways to travel faster, safer, and farther. As early Americans steadily moved westward, our technological capacity grew. All around this nation, people held steadfast to the myth of natural resource inexhaustibility. Berms and bridges were built to connect wagon trails and to reach further into the fruitful wildlands. The Ford Model T is an emblem of American ingenuity, which inspired asphalt pavement technology and more and more roads. In 1959, Dwight D. Eisenhower proposed the Federal Highway Act, to liberate and protect the American public. The project took 35 years to complete (Blas, 2010). However, it wasn’t until 1977 that wetlands became federally protected. Still, landowners and project managers can apply for a waiver permit to backfill or alter wetlands. Due to this history, our roads not only shape American culture, they shape the future of American wildlife.

One group of wildlife particularly imperiled by road-related wetland loss is early spring amphibians. These frogs and salamanders spend winters underground in upland forests, emerge in March and April, and begin travelling toward their historic breeding wetlands. These populations have been following the same route for hundreds of generations, and will continue to do so if we build a road that crosses their path (Forman, et. al., 2003). Unlike other wildlife, amphibians have no behavioral adaptations to respond to cars (Forman, et. al., 2003). Specifically, they have reduced eyesight and reduced hearing, and when threatened they freeze in an attempt to not be noticed by a predator (Vitt & Caldwell, 2013). These animals are also ectothermic, meaning they cannot generate their own body heat. When an amphibian encounters a warm spot in the environment, it will pause in an attempt to absorb warmth (Vitt & Caldwell, 2013). Usually, these warm places are sunny forest floors or rocks, but the dark surface of roads readily absorbs heat from the sun. In the cool spring, these roads are very attractive to amphibians, and many will bask for an extended period of time. In conjunction, these factors greatly increase the chance that amphibians will be struck by passing vehicles (Forman, et. al., 2003).

Roads are our nation’s circulatory system, but Americans are increasingly becoming concerned with the ways in which our automobile culture is impacting environmental health. In a poll from 2013, 80% of respondents felt that working to restore and enhance the natural environment was fairly or very important. Twenty-two percent also reported having walked or bicycled instead of driving in the past few months. However, 33% felt that government spending on restoration should be decreased (YouGov, 2013).

Transportation agencies are responsible for maintaining safe, effective infrastructure that improves the lives of people. These goals are not separate from ecological concerns. With 80% of the population wanting more ecological restoration at a lower price, we must adopt new policies that address these groups simultaneously. Therefore, we propose the implementation of site-specific methods of reducing amphibian road mortality by integrating transportation agencies and local conservation organizations with common goals.

The Role of Amphibians

It is important to maintain amphibian populations because they play key roles that maintain the quality in ecosystems, Amphibians are often used as indicator species, because they reflect the healthiness of an ecosystem. “Amphibians breathe through their skin, so they are much more directly affected by changes to the chemistry of air and water associated with pollution” (Brewer & Alaback, n.d.). If anything impacts their habitat, it will be seen in their population size. This can serve as a warning to people monitoring, showing that something could be wrong.

Amphibians also are the most efficient at spreading nutrients throughout habitats. In a study by Davic and Welsh (2004) monitoring phosphorus among animal populations, salamanders alone had 60% more than both birds and small mammals combined. Amphibians also prevent carbon from being released into the atmosphere through the consumption of decomposers. Richard Conniff from the New York Times (2014) found that at normal populations, woodland salamanders can prevent 179 pounds of carbon per acre from being released into the atmosphere. If roads fragment the migration paths of amphibians then how can nutrients be spread effectively?

Amphibians also regulate activities within ecosystems. For example tadpoles help provide a basis for many food chains by both feeding on algae and providing food for other organisms (University of Georgia, 2008). Mokany and Shine (2003) say “They [(tadpoles)] are effective grazers, capable of reducing algal abundance” (p 615). Without tadpoles consuming algae in these wetland habitats algae can take over bodies of water and contaminate the water sources for other animals. Amphibians are also regulators of insects and benthic macro invertebrates, such as insect larva. Batzer and Wissinger (1996) state: “tadpoles of many salamanders and a few frogs and toads are predatory and, in some habitats, can regulate the abundance of insects and influence the size distribution of their communities” (p. 88). Without these predators in an ecosystem insect populations will have less controlling factors, predatory populations limiting the population of their food, leading to higher populations of insects. This can be concerning when insect populations carry diseases that cause people to use commercial propellants to stop them.

Creating safe migration opportunities for amphibians may seem expensive, but commercial fertilizers and pesticides have other more insidious expenses. Although there are commercial methods to controlling insect populations and providing land and animals nutrients, they usually lead to more pollution within habitats. The pollution can have a wide variety of negative effects on the ecosystem. Chemicals can be caught in rain flow runoff corrupting the soil, killing off plants and causing defects in new born animals. If fertilizers flow into waters they can kill off aquatic life and cause algal blooms, vicious growth of algae which can overtake other organisms, use up all nutrients within an area and suffocate organisms with too much oxygen from cellular respiration. Khan and Law (2005) state:

Pesticides and related chemicals destroy the delicate balance between species that characterizes a functioning ecosystem. Pesticides produce many physiological and biochemical changes in freshwater organisms (p 315).

Frogs have been known to lack limbs or in some cases become feminized, changing genders due to chemical disruption of sexual growth. Allowing amphibians to maintain ecosystems in the long run can be cheaper than continued purchase of commercial fertilizers and repellants and can be as effective.
Habitat Fragmentation

The installation of road networks can sever corridors between amphibious habitat, thus resulting in the isolation of populations (Lehtin, Galatowitsch, & Tester, 1999). Isolated amphibian populations are more likely to lose genetic diversity and become homozygous, which means having two identical pairs of genes (Anderson, Fog, & Damgaard, 2004,). This is an issue because if all individuals have the same genes and an event such as a disease or an environmental catastrophe occurs, then the entire population could go extinct because every individual would be affected the same way. Lehtin, Richard, M., Galatowitsch, Susan, M., Tester, John, R., (1999) write that proximity of populations was important and if they are too separated that “isolated populations …were more likely to experience stochastic extinctions” (p.2). The habitats that amphibians occupy are usually non-continuous, therefore they rely on migrating to nearby habitats to complete their life cycle and exchange genetic material. However, amphibians have low dispersal rates and roads act as barriers between habitats. Dixo, Metzger, Morgante, and Zamudio (2009) state that:

As a result [of anthropogenic fragmentation such as roads], isolated sub-populations become the units on which genetic drift, inbreeding and selection act [35,59-61] and without the ameliorating influence of gene flow, their concerted effects impose a more rapid erosion of genetic diversity, exacerbating fitness reductions and extinction risks (p. 50).

Isolation and loss of genetic diversity are contributing reasons why nearly one third of amphibian populations are threatened (Kiesecker 2010). Constructing more roads to gain access to more natural resources may be lucrative, but it doesn’t compare to the consequences resulting from a loss of biodiversity.

When populations become isolated individuals have no choice but to breed with relatives, this causes inbreeding depression. Inbreeding depression, as defined by Zimmer and Elmen (2013), is “a reduction in the average fitness of inbred individuals relative to that of outbred individuals. It arises because rare, recessive alleles become expressed in a homozygous state where they can detrimentally affect the performance” (p. 185).

Anderson, Fog, and Damgaard (2004) state that inbreeding depression directly coincides with fragmentation and the bottleneck event. The bottleneck event is an event “in which the number of individuals in a population is reduced drastically. Even if this dip in numbers is temporary, it can have lasting effects on the genetic variation of a population” (Zimmer & Elmen, 2013, p. 164). By severing wildlife corridors in forests we are isolating non vagile, or not far dispersing, populations and forcing individuals to breed amongst themselves thus increasing homozygosity. Inbreeding depression puts amphibious species at serious risk for extinction, when homozygosity increases heterozygosity decreases.

Although amphibious species decline doesn’t appear to be something of grave concern it is something that humans have induced and it is our responsibility to ensure that these populations persist. Most people would not think twice about killing an amphibian with their car, after all they are crossing our road networks. However, most people are also unaware of the critical state amphibians are in and are uneducated about the effects of not having these species in our environment. Roads deter many amphibians from crossing, no matter how wide the road, and force species to return to their original habitat to mate (Marsh, Milham, Gorham, & Beckman, 2005). Inbreeding, amongst other factors, poses a serious threat to the persistence of our already declining species of amphibious friends.

Road-Effect Mitigation

Using a multi-approach method for reducing amphibian road mortality is both more ecologically effective and economically efficient than any single measure. In his academic review, Daigle (2010) claims that by beginning with a comprehensive analysis of the sites in need of mitigation, planners can develop roads that simultaneously meet the public need, prevent future liability and encourage benefit capture, prevent or reverse environmental damages, all while meeting road management funding restrictions.

Additionally, Jackson (2003) states that careful consideration is required before building a culvert-type road passage structure, since certain conditions of size, moisture, and fencing type may hinder species movement. Therefore, Jackson (2003) recommends that tunnels should only be used when you have a known population at risk, know where their migration path crosses the road, if rare species are present, when traffic volumes are high, or when the species depends on high survival rates of adults, as is the case with mole salamanders. Furthermore, Jackson (2003) claims that these tunnels are only worth it if there is enough careful planning, construction, and maintenance in place to ensure proper conditions, and other small animals in the area are unlikely to be disrupted by the tunnel.

In cases where some of these measures aren’t met fully, such as low traffic volume areas with rare mole salamanders, temporary road closures could be implemented to effectively mitigate road mortality. In their synopsis on global amphibian conservation, Smith and Sutherland (2014) recount a German study by Karthaus (1985), which looked at common toads (Bufo bufo) and their crossing success with and without traffic on a 400 meter stretch. While traffic was active, where no toads crossed successfully. An hour after the section of road was closed, over 100,000 toads were counted as crossing successfully.

Seasonal road closures are arguably the closest we can get to a highly effective and very low cost solution to road-effects. If a mere 400 meters of closed road can allow hundreds of thousands of amphibians safe passage, there is no reason not to do so. In rural areas particularly, there is little chance that the closure would include private driveways or other roads, and if they did these residents would of course still have access to their homes. However, in some cases these closures may require some drivers to take large detours. By taking the time and seeking expertise before undertaking a road-effect mitigation strategy, we can better ensure that the project will be successful.

Public Information and Outreach

Little information exists on the restorative effects of implementing wildlife corridors. According to Scott Jackson, we do not need statistics to be confident that connecting wildlife habitats with corridors will increase genetic diversity and the overall persistence of the population (Personal communication, 2014). Wildlife corridors are clearly effective, however the only way for them to be established is if awareness is raised on why they are necessary.  Beckmann, Clevenger, Huijser, and Hilty (2010) developed a training course called Road Ecology: Habitats and Highways, the purpose of the course was to organize individuals to monitor wildlife movement and collect field data. The assessment of the effectiveness of this training became much more than just data collection, “the greatest value of these trainings was in developing awareness of habitat connectivity among transportation professionals and the agency staff who work on transportation issues” (Austin, Slesar, & Hammond, 2010, p. 247). If enough of the general public became interested in saving amphibious populations then they could contact state and local governments to get funds allocated in order to implement wildlife corridors.



Though there is now the theoretically feasible chance of resurrecting wooly mammoths from extinction, the reality is that there is no simple, cost-effective, and ecologically sound way to restore extinct species. The only way to combat these ecological, social, and economic losses is to prevent the extinctions in the first place. Through using a multi-approach policy, raising awareness, and allocating sufficient funds we can begin to reverse the effects that roads have had on amphibian populations. Like so many current issues regarding sustainable infrastructure, the initial costs are high, but the return on the investment results in a profit. Some argue that conservation is putting the needs of people behind those of plants and animals. However, it is important for us as a species to realize that the effects of the decisions we make for non-humans have real, tangible outcomes for individual people and our society as a whole.


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