The amphibians have taken to the road. On how not to thwart their plans

Every spring, especially during wet and warm nights, Polish roads become the arena of dramatic migration. Under the cover of darkness, amphibians embark on their journey. Gray toads(Bufo bufo), grass frogs(Rana temporaria), newts and spotted salamanders(Salamandra salamandra) move, aiming for bodies of water where their species have been laying their eggs for generations. But for many of them, the asphalt pavement is an obstacle they fail to cross. Hundreds and sometimes thousands die each night under the wheels of cars, leaving a gap in the delicate balance of ecosystems. What can we do before the silent guardians of our waters and forests disappear?

Why do amphibians migrate and where is the source of the problem?

Amphibians are aquatic animals, which means that they regularly change their habitat during their lives. In early spring, they move from their overwintering sites (often damp forests, meadows or thickets) to bodies of water, where they breed. After spawning, adults return to land, and after a few months young individuals move in their footsteps. Gray toads can travel from several hundred meters to several kilometers during this period, following instinct and fixed routes. Water frogs or lake frogs even 15 kilometers. These migrations are a prerequisite for the survival of amphibian populations, but in agricultural and urban landscapes they can sometimes be deadly.

The main threat to migrating amphibians is the road infrastructure that crosses their traditional routes. Amphibians move slowly, and their defensive reactions are insufficient to avoid collisions with oncoming vehicles. Particularly in areas of intense migration, amphibian mortality can be very high, reaching 30 to as much as 50 percent of local populations in some locations.

An important factor in the high mortality rate is philopatry, or the strong fidelity of amphibians to traditional breeding and migration sites. The migratory routes of these animals are relatively constant over time, which means that the appearance of new barriers, such as roads, does not change their behavior. Amphibians consistently try to overcome these obstacles, leading to mass extinction.

What are we breaking down on Polish roads?

During spring amphibian migrations, species with very specific ecological requirements are particularly visible and endangered. One of the most common and also the most frequently encountered species on the roads is the gray toad(Bufo bufo). It is a large, massively built amphibian with gray-brown coloration, whose body is covered with characteristic warts. Due to its slow movement, the gray toad is particularly vulnerable to being swatted. Its migration usually takes place in early spring and involves moving from wintering grounds – often forests, fields and meadows – to bodies of water, where females lay their characteristic long strings of eggs.

Another species regularly found on Polish roads is the grass frog(Rana temporaria). It is smaller than the gray toad, more delicate, and its coloration can vary from olive to various shades of brown. A distinctive feature of this frog’s appearance is a dark temporal spot behind the eye. This species is often seen in wet areas: meadows, marshes, river valleys and damp forests. In the spring, it migrates, like other amphibians, to shallow bodies of water, where it lays eggs in the form of gelatinous clusters of scutes.

Among newts, the great crested newt(Triturus cristatus) is particularly vulnerable to the dangers of migration. This species is under strict protection, covered by active protection. It prefers clear bodies of water, such as ponds or lakes, where it does its mating. Males are easily recognizable during the mating season due to the high serrated crest running along the back and tail. Unfortunately, the migration of this species often takes place across the road, so that many individuals fail to reach their breeding sites.

A rarer but highly distinctive amphibian that shows up during migration is the spotted salamander(Salamandra salamandra). This species is characterized by its unique appearance: its black body is covered with bright yellow spots, acting as a warning function for potential predators. Salamanders prefer moist deciduous forests, often near streams or springs. In Poland, they are found mainly in mountainous regions – in the Sudetes and the Carpathians. Interestingly, they do not lay eggs, but give birth to live larvae directly into the water, where they continue further development. Despite their rarer occurrence, salamanders are sometimes victims of traffic. Their contrasting coloration can draw the attention of drivers, although not always early enough.

Ecological impact – why is it important?

Roads are a difficult barrier for amphibians, effectively separating individuals of the same species, originally belonging to one population. Spatial isolation maintained over a long period of time leads to fragmentation of the population, which reduces gene flow and results in depletion of its genetic diversity. As a result, the risk of mating between closely related individuals increases, leading to reduced viability, deterioration of the population’s condition and a decline in its numbers.

Amphibians perform important ecological functions, occupying positions as both predators and prey in trophic networks. As predators, they effectively regulate the abundance of many groups of invertebrates, especially insects, including species considered a nuisance to humans. At the same time, they themselves are an important component of the diet of numerous prey species, such as birds, mammals and reptiles. A significant decline in their populations can therefore lead to significant ecological imbalances, resulting, for example, in an increase in insects and a decline in the populations of predators that depend on amphibians as a food source.

Moreover, amphibians are bioindicators – their numbers and condition are indicative of the state of the environment. High road mortality, combined with habitat loss, climate change and water pollution, is contributing to drastic population declines in many species.

Amphibians are a poorly studied group of animals, and the problem of their protection on roads is not looked at on a large scale. Culverts are being built in large numbers, but they are often placed based on insufficient information. The ‘arming’ of a given road section with culverts often depends more on the quality of the inventory than on the actual number of amphibians in the area and the degree of their vulnerability – says Mikolaj Kaczmarski, PhD, from the University of Life Sciences in Poznan, in a statement for the Science in Poland portal.

How can we get involved in amphibian conservation?

We are not helpless. There are several ways we can reduce the number of amphibians dying under the wheels of cars:

• Reduce speed in forest sections and near bodies of water

In areas of regular amphibian migration, especially in spring, it is advisable to reduce driving speed. The presence of amphibians on roads is usually signaled by special road signs. Careful observation of the road surface makes it possible to avoid too close an encounter with migrating individuals. In addition, in selected regions of Poland, such as Lower Silesia, educational campaigns are being implemented to raise the environmental awareness of drivers in this regard.

• Support for initiatives to build amphibian crossings

An effective solution to the problem of road mortality of amphibians are specialized infrastructure structures, such as underground tunnels and guiding barriers, which allow migrating animals to safely cross roads. These solutions have long been successfully operating in countries such as Germany and the Netherlands, and their implementation is also observed in Poland (e.g. in the Białowieża Forest region). It is necessary to continue promoting and supporting local initiatives to implement similar technical solutions in other regions of the country.

• Involvement in relocating amphibians

Annual actions to relocate amphibians through particularly dangerous sections of roads are carried out by environmental organizations and volunteers, including the Polish Society for Nature Protection “Salamandra,” PTOP and other NGOs. Active participation in such initiatives significantly reduces animal mortality and facilitates the preservation of local amphibian populations.

• Protection of wetlands from degradation and drainage

Bodies of water and marsh ecosystems are breeding grounds and habitats for amphibians. Degradation of these habitats through drainage, reclamation or logging is one of the main factors threatening populations. It is important to promote and enforce conservation measures aimed at preserving the integrity and sustainability of wetland habitats and riparian forests as essential elements of biodiversity conservation.

Awareness and education

The fight to protect amphibians is not only about action on the ground, but also about education. The more people learn about the problem, the greater the chance of implementing effective solutions. Even simple actions, such as paying attention to warning signs or avoiding unnecessary splitting of puddles and roadsides, can help reduce the loss of amphibian populations. Every toad or frog rescued is a step toward a healthier ecosystem – and ultimately a better life for us as well.

In the article, I used, among others. z:

1. Kałuża M., Kamiński B., Gajewski S. (2015). Collisions of amphibian migration routes with communication infrastructure of Poznań. Nature Conservation Management in Forests
2. Flesch A. (2023). Monitoring of mortality and migration of herpetofauna on state road 22, in the vicinity of the Warta Mouth National Park – period 2020-2022, Nature Review, 34(2), 45-60.
3. Kolanek A., Turniak E. (2020). Evaluation of the effectiveness of methods of active protection of gray toads Bufo bufo on the example of the population from the Wroclaw Zalesie. Nature Review XXXI, 4 (2020) 56-68.
4. Kurek, R., Rybacki, M., & Soltysiak, M. (2011). A guide to amphibian conservation. Bystra, Pracownia na rzecz Wszystkich Istot Association.
5. Hels, T., & Buchwald, E. (2001). The effect of road kills on amphibian populations. Biological Conservation, 99(3), 331-340