Canadian Herpetological Society

Société d'herpétologie du Canada


| Tunnels | Walls and Fences | Project Summaries | Amphibians and Roads |

In most parts of Canada we encounter road kill on almost a daily basis. Whether it is raccoons, rabbits or even the occasional large bird, it is a common sight. Thoughts of pity, disgust and annoyance are common, but have you ever considered that wildlife killed by motorists may actually pose a real threat to the survival of a population? In the case of many amphibian species this is a sobering reality. Unlike larger species, dozens of amphibians could be killed by a single vehicle in a short period and not even be seen or noticed. A large number killed over a relatively small area, especially if the roads are already wet, could make driving conditions slick and perilous. With these concerns in mind municipalities, environmental organizations, and volunteers have conducted toad rescue programs and installed 'toad tunnels' in many localities in Europe and the United States. At first these projects may seem unfamiliar or even comical but the reasons behind them are both serious and fascinating. Interest in these tunnels is still relatively low in Canada, but recent work on a snake tunnel suggests that it is growing.

Who needs amphibians anyway?
While this all my sound sad and gruesome you may be asking, "Well, who really needs amphibians anyway?" and that is a good question! First of all, amphibians are among the best wildlife for educational and enjoyment purposes. With a virtual symphony of voices they enhance the excitement of spring on a warm April evening and, due to their generally harmless nature, make excellent educational wildlife for children to hold in their hands. They also provide pest control, especially if they are present in your backyard garden. Toads and frogs are both strictly carnivorous and feed on grubs, slugs, ants, flies, mosquitoes and their larvae worms, many other insects, invertebrates and smaller fish and tadpoles. Finally amphibians are important to science, as they are sensitive to environmental change and therefore effective indicators of wetlands health. For more on the importance of amphibians (and reptiles) see the rest of the CARCNET site.

Amphibian migration theory
The need for amphibian tunnels stems directly from the need for amphibians to migrate. The word amphibian comes from 'amphibious' which means capable of living both on water and on land {Steen, Edwin B., Dictionary of Biology, Barnes and Noble, New York, 1971). Thus, most amphibians spend part of their life cycle in the water and part on land. This reality causes many amphibians to stage impressive migrations between breeding ponds, upland summering areas and wintering sites. On the contrary, several species of salamanders including the Common Mudpuppy may remain active under winter ice.

Each spring millions of amorous amphibians are drawn to marshes, ponds, lakes, creeks, pools and even puddles to breed. They are influenced by hormonal changes, which are stimulated by increased temperatures and moisture, and evidence suggests that the reflection of moonlight from the surface of wetlands may be an attractant. However, amphibians often migrate on warm, rainy nights in the spring when clouds would obscure the moon. Females are attracted to males by their vocalizations. Some species are more loyal than others in returning to their birthplace, while others it seems will deposit their spawn in the first stagnant pool of water they find

The breeding sites are utilized for the summer by developing young and the adults, who also use the surrounding land for feeding. In the fall, the newly developed young and the adults that have summered in wetlands move to higher, drier sites to over winter. However, this trek to their hibernation sites often involves the perilous navigation of a busy road. Often this journey is less than 2 km but maximum distances have been estimated as high as 7 km for some species and populations.

Why amphibian tunnels?
A high incidence of amphibian mortality has been recorded in many locations. In some places, such as Oregon, the numbers of toads killed by automobiles has a significant effect on the population. An effective tunnel system would reduce traffic-related deaths by nearly 100 % and thus virtually ensure the survival of that population unless other factors played a role. In other areas just the fact the amphibians are being killed in large numbers have motivated conservation organizations to take an active role in conservation.

Beyond the obvious fact that tunnels prevent deaths they also afford other benefits. Scientific research may be conducted on tunnel effectiveness and amphibian migration. For example:

  • Scientists from the Schaffhausen Society for Scientific Research showed that the amphibian population successfully utilized the tunnel built in Switzerland in 1969
  • in Amherst, Massachusetts migrating Spotted Salamanders were monitored and it was discovered that light levels may influence migration
  • the Madingley Toad Rescue identify migrating amphibians to age, (juvenile or adult), sex and species and monitor numbers. They also insert 'PIT' tags (passive integrated transponder) for future identification of toads.

New projects provide opportunities to engineer new designs that are cheaper and more effective. Since a tunnel would only be necessary where a migration route encounters a major road the construction would be immediately noticed by many people, thus increasing public awareness. Safety concerns issues would be resolved because, as previously mentioned, amphibian carcasses on slick roads present a hazard to motorists.

These tunnels are often referred to as 'toad tunnels' because toads are at a greater risk than other species for several reasons.

  • they are slower than frogs and salamanders
  • they often move in large numbers and concentrations compared to other species and are thus killed in large numbers
  • research suggests that certain species of toads are very faithful to the breeding ponds where they were born, and return year after year, keeping the same migration route

Finally, in contrast to other methods, properly constructed and effective tunnel and fence systems provide permanent solutions and do not require supervision.

Factors affecting site selection :
Before a tunnel is installed there are several factors to be considered, namely:

  • Size of amphibian population
  • Direction of migration
  • Most intensively used routes
  • Mortality rate
  • Amount of traffic on the road
  • Width and nature of the road

Other measures taken to save amphibians from road-related fatalities.

Other efforts to rescue amphibians have been employed aside from the construction of tunnels. These efforts have often proved to be preliminary to the construction of tunnels. Locating migration sites, manually rescuing amphibians, posting signs, constructing breeding ponds, and raising public awareness all fall under this category.

Environmental organizations in the United States, United Kingdom and Hungary have recruited volunteers to patrol roadsides on nights of heavy migration to capture and transport amphibians across the road. Temporary drift fences and collection buckets are set up and volunteers equipped with lights forewarn approaching motorists.

In Hungary, for example, the Toad Action Group (TAG) successfully transported 8,600 amphibians in 1988 including 2500 frogs and toads from a single site ! In addition, the Madingley Toad Rescue in England rescued more than 30,000 amphibians between 1994 and 1999 while recording only about 2000 casualties. This proves that an effective rescue program rivals the efficiency of a tunnel.

In addition to this, some sites in Switzerland and the United Kingdom have newly constructed breeding ponds on the side of the road where toads are coming from. If adopted, these ponds would significantly lower the numbers of amphibians migrating and a temporary barrier would restrict access during peak movements, allowing volunteers to continue to process of transporting migrants across the road.

Large, bright signs with a stylized toad logo have been used in Germany, Switzerland and the Netherlands since the late 1960's and early 1970's. In 1979 an adapted version of this sign was used in Wales, a first for the United Kingdom. Since that time more than 200 sites in the United Kingdom and Europe have signs posted. The purpose of these signs is to warn motorists of toad migration sites so that they may avoid them during the evening hours of peak migration or slow down while passing. The speed limit is rarely lowered however, some roads, most notably in Switzerland, have been closed during peak migration times. These signs serve to protect toad and human lives as they advocate slowing down to wait for large number of amphibians to pass. Swerving around the animals is not advisable as an accident may result.

Where are the tunnels?
Amphibian tunnels have been constructed at literally dozens of sites in several countries around the world. These include:

  • the United Kingdom has many professionally designed sites, especially England.
  • the United States has tunnels in Texas, Massachusetts and California with potential sites in Oregon and Florida
  • Germany has many sites. In the states of: Lower Saxony, Baden-Wurttemberg, Schleswig-Holstein and Bavaria, construction and study of toad tunnels since at least the 1970's. A few projects are summarized in a chart under Project summaries.
  • in Switzerland on the Turlersee there are about 20 tunnels over a 50m distance. On the Etang de Sepay, near Lausanne, a single tunnel exit was monitored during spring 1970 and 400 toads were found to use it. In fact, the local highway authority near Neeracherried, Switzerland constructed one of the first experimental amphibian tunnels in the world in 1969.
  • Snake tunnels have been installed and monitored in Manitoba, Canada.

Tunnel designs
Many different designs have been experimented with over the past 30 years however, the more successful projects have all incorporated some sort of low fencing or barrier to prevent access by the migrating amphibians to the road and, ideally, to guide them to a tunnel entrance(s).

Original tunnel projects often utilized existing drainage culverts by simply adding a drift fence. Other simple designs used PVC piping and steel tunnels however, steel has been deemed ineffective due to a high conductivity of cold. Concrete has been widely used with the major concerns being the microclimate inside and amphibians ingesting any pieces which may flake off. Migrating amphibians are hesitant to enter tunnels with a microclimate that is significantly different from their surroundings. Light, air and humidity levels are all important factors. To correct these problems tunnels have been built with larger diameters to allow a greater air flow, while other grated tunnels have been built flush with the road to allow all ambient light, air and moisture to enter and pass freely through the tunnel.

Another problem has been tunnel entrances. Three examples include 'swallow tail', 'standard' and 'one-way' entrances.

The 'swallow-tail' entrance employs a barrier across the middle to block amphibians from hopping right past the entrance. Two short, curved walls extend from this centre wall to further guide animals.

The 'standard' entrance is simply a drift fence or wall angled towards an open tunnel entrance.

A final example is the 'one-way' entrance which has been used in Switzerland. The entrance is lower than ground level and causes amphibians to drop into the tunnel, making escape difficult. From this point they move through and exit by dropping from a small height above ground level. This feature prevents amphibians from entering at the wrong end as a second tunnel with the same design moves animals in the opposite direction. This designs requires that two tunnels always be built in conjunction with one another.

Walls and fences:
Walls and fences are an important constituent of amphibian tunnels. They function to restrict access to the road while ideally directed amphibians towards tunnel entrances. They have been constructed of polythene, a rigid plastic, and concrete. Berms of sloping earth often complement wall designs.

One of the major problems associate with these 'drift fences', as they are often called, is wildlife becoming trapped on either side of them. A concrete wall design which resembles the quarter section of a tunnel has a small 'step' and an overhang. The step serves to encourage the amphibians to stay in the funnelling system while the overhang eliminates the possibility f clambering over. The front of the fence is level with the ground. The ground which meets the back of the tunnel angles upward and away from the top which allows animals which do make it on to the road to retreat and drop down over the fence.

Fortunately most fences are less than 1.5 feet in height which would allow any mammal that was medium sized or larger to clamber over. Those which are small enough may utilize the tunnel if they are attempting to cross the road. However, the design mentioned above allows amphibians which may otherwise become trapped to make it back safely.

Studies suggest that the fences should 'zig-zag' and amphibians should encounter them at an angle of less than 60 degrees (relative to the tunnel entrance) or they may otherwise turn back. This design funnels amphibians to every tunnel entrance in a /\./\./\./\ pattern with tunnels represented by the periods.

Ideally they should be durable, effective and relatively easy to install. They should create a barrier to all amphibians across the entire length of a migration corridor to effectively reduce road fatalities to virtually nothing.

Cost (approximate $U.S. funds) and other economic factors
The cost of installation varies depending upon materials used, amount of fencing, number and design of tunnels, disruption of road bed, and the availability and cost of materials. Prices have ranged from one tunnel around $ 2,000.00 to a system of tunnels and fencing around $40,000.00. The development of more efficient methods of installation will serve to reduce the cost and allow toad tunnels to enjoy more widespread use.


| Salamander Tunnel in Amherst | Gartersnake Tunnels in Manitoba
| Amphibian Tunnels in Germany | Spotted Turtle Tunnel |

"U.K.'s first toad tunnel aims to save thousands from croaking under cars"

The Toronto Star, Saturday, March 14 1987

Britain's first ever 'toad tunnel' was officially opened on March 13, 1987 by Environment Minister Lord Skelmersdale in Hambleden, Reueter about 80 km west of London. The tunnel was designed and built by ACO Polymer Products who have designed concrete and plastic polymer products for other wildlife projects in the United Kingdom.

The Fauna and Flora Preservation Society, along with the Department of Transport launched a 'Toads on Roads' campaign in 1984 to raise public awareness and the necessary funds to take action against an estimated 150,000 amphibian deaths, or approximately 20,000 kg, by motor vehicles in the United Kingdom every year.

Previous to the building of the tunnel volunteers had used flashlights and buckets to aid the amphibians in their treacherous journey across the road. The tunnel itself is built of polymer concrete and is 20 cm in diameter. A fence made of rigid polythene stretches 30 cm high across a distance of several hundred metres to guide amphibians to the tunnel entrance. An estimated 10,000 toads cross this road in 5 days in early march or approximately 500 per hour and the tunnels may be used by other wildlife

ACO Wildlife: Amphibian Tunnel and Fence Systems

A summary:

ACO Polymer Products Ltd. specializes in plastic and concrete polymer products for a variety of projects but specialize in drainage. As such, they have become quite involved in the construction and development of toad tunnels. Their wildlife department has also constructed polymer products for several conservation efforts involving birds. Their website is:

ACO Polymer Products Ltd.
ACO Technologies plc
ACO Business Park
Hitchin Road
Shefford, Bedfordshire, UK
SG17 5TE
Tel: +44(0)1462 816666
Fax: +44(0)1462 815895 Email:


Recent projects as of May 2000:

  • private individual installed ACO Toad Tunnel through their garage which had been built on the path to the mating pond
  • 1600 metres of amphibian fencing has recently been installed at an industrial site in Cheshire
  • 4100 metres of amphibian fencing recently supplied to West Sussex County Council for a development in the Ouse Estuary, Newhaven
Description / Part No. Length
Amphibian Tunnel: 0500 100 20 40 90
Tunnel Entrance Unit: 0523 65 60 42 20
Wildlife Fence: 0520 100 52 40 8.2
Wildlife Fence Post: 0521 88 NA NA NA

Wildlife Fence:

  • made of recycled plastic moulding
  • concave barrier to approaching amphibians
  • prevents access to road
  • guides amphibians to tunnel entrance
  • some fences may trap other wildlife on road side
  • curved away from the road to allow trapped animals to clamber over
  • recycled plastic pole supports the front
  • easily cut with a wood saw for specific projects

Amphibian Tunnel:

  • Used a large industrial drain: the Q200 manufactured by ACOPP
  • made from polymer concrete
  • absorbs water differently than typical concrete (does not remain as moist under wet conditions) and therefore is more conducive to movement
  • top of the tunnel lies flush with road surface
  • tunnel has slots on top to allow air, light and moisture in
  • micro-climate similar to surrounding area

Tunnel Entrance Unit:

  • made from strong recycled plastic sheet
  • wildlife fence connects to tunnel entrance
  • dividing wall prevents amphibians from passing by the tunnel entrance
  • optional 'swallow tail' to assist in guiding to the tunnel

An excellent book is available on amphibian tunnels and related topics. Details of the book including a table of contents and ordering information is included below.


Proceedings of the Toad Tunnel Conference
Rendsburg, Federal Republic of Germany, 7-8 January 1989
Edited by
Thomas E.S. Langton

To order a copy of this book please contact:
Sherly Carter
ACO Wildlife
ACO Polymer Products
Hitchin Road, Shefford, Bedfordhire
SG17 5Js, England
Tel.: 01462 810201

Note: The cost of the book including shipping and handling is approximately $35.00 Canadian funds. CARCNET contacted Sheryl via e-mail, sent a credit card number and received the book within 10 days


  • Foreword - His Royal Higness Prince Philip, Duke of Edinburgh
  • Preface - Martin Holdgate
  • Section I. - Review of Systems: Objectives
  • A survey of amphibian preservation at roads in Switzerland - Jan Ryser & Kurt Grossenbacher
  • Protection of amphibians on roads - examples and experiences from Lower Saxony. - Richard Podloucky
  • The acceptance of 0.2 m tunnels by amphibians during their migration to the breeding site - Kuno Brehm
  • Investigations into the protection of migrant amphibians from the threats from road traffic in the Federal Republic of Germany - a summary. - Ralf Dexel
  • Protection for amphibians on roads in Nordrhein-Westphalia. - Reiner Feldmann & Aeno Geiger
  • Experience and problems with a toad tunnel system in the Mittlegebiege region of West Germany Holger Meinig
  • Amphibian and reptile tunnels in the Netherlands - Anna Zuiderwijk
  • Reasons for preventing amphibian mortality on roads - Thomas E.S. Langton
  • Animal subways - views of an animal protectionist and green politician - Haunete Luukkainen
  • 'Toads on Roads' in Belgium - Donato Ballasina

  • Section II. - Physical and biotic variables. Orientations and behaviour
  • …dark zones': two examples of tunnel and fence systems - …ski
  • Effectiveness of drift fences and tunnels for moving spotted salamanders Ambystoma maculatum under roads - Scott D. Jackson & Thomas Tyning
  • Investigations into the influences of roads in the genetic structure of populations of the common frog Rana temporaria. - Wolfgang Reh
  • Opportunistic predation of common toads Bufo bufo at a drift fence in southern England - Christopher J. Reading
  • Migratory behaviour of the common toad Bufp bufo and the natterjack toad Bufo calamita - Ulrich Sinsch
  • Pilot project Braken: preliminary results from the resettlement of adult toads to a substitute breeding site. - L. Schlopp, M.Kietz, R.Podloucky & F.M. Stolz.
  • The behaviour of migrating anurans at a tunnel and fence system - Thorston Buck-Dobrick & Regine Dobrick
  • Tunnels and temperature: results from a study of a drift fence and tunnel system at Henley-on-Thames, Buckinghamshore, England - Thomas E. Langston

  • Section III. Drift Fencing: design and construction. Tunnel materials and installation
  • Potential tunnel systems at road developments in England - Robert Oldham
  • Amphibians Barriers in mid-Wales - Frederick M. Slater
  • Migration of toads during the spawning season at Stallauer Wiether Lake, Bad Tolz, Bavaria - Hans Haslinger
  • Amphibian Fencing - Keith F. Corbett
  • Amphibian protection on highway A71 in Sologne, France - Philippe Herny & Catherine Epain-Henry

  • Section IV. - Concluding discussion. Questionnaire

For brief summaries of a few of ACO's toad tunnel and other wildlife projects.
Madingley Toad rescue. Excellent site with a great deal of information.