Design a tunnel to help frogs safely cross a path or road.
This activity is designed to teach students about the threats amphibians face from cars when crossing roads. As students are introduced to the concept of wildlife crossings, they also learn about local amphibians and their seasonal movements.
Millions of frogs are killed every year by cars. Frogs cross roads to reach their mating ponds and for other seasonal movements. With so many frogs dying on the way to mating, entire populations are in danger of collapse. Many amphibian species even risk going extinct due to roadkill. Death from cars is a major problem for frog populations around the world.
"Toad Tunnels" - A Brief History
In the US, the first tunnel for frogs was built in Davis, California in 1995. This tunnel was built to help amphibians cross the Pole Line Road overpass. The entrance was affectionately named “Toad Hollow” and features a toad bar, toad outhouse and toad hotel.
Later, in 2003, a group of Cornell University students designed and built fences to help guide amphibians through tunnels that already existed beneath the road. These fences helped guide amphibians to spring breeding ponds in Cornell’s Botanic Gardens. Their efforts were effective at reducing amphibian deaths from roadkill.
Frog Seasonal Movements
During autumn, frogs eat as much as possible to prepare for winter. In late fall, frogs move to their wintering grounds. Frogs overwinter deep in the soil, in compost heaps, under rocks, in dead wood, log piles or in other hidden, protected crevices. While many aquatic frogs hibernate underwater, toads hibernate on land.
Frogs stop hibernating as the weather warms up in the early Spring. As night time temperatures reach over 40 degrees Fahrenheit, frogs emerge from their hibernation. This process may start as early as late January. Local weather temperatures determine the precise time when hibernation ends.
After hibernation, frogs make their way to ponds or bodies of water to mate. Frogs typically breed in March and April. Males migrate first to the ponds to find their preferred location. Then, the females follow.
When spawning is over, frogs typically leave the water and stay mostly on land until the next season.
Step 1: Learn about your Local Frogs
The first step in our September activity is to learn as much as possible about your local frogs.
What species are local to my community? Where do these frogs prefer to overwinter? Where are their mating ponds?
Listen at night to croaking. Try to identify the species. Learn about your frog's seasonal movements.
While most frogs are nocturnal, they can still be found during the day with a good eye. Frogs love moist homes under a log, in the mud or hidden behind rocks.
Right after the rain is a great time to find frogs. Toads prefer a wet environment to keep their skin moist. After the rain, the air is cool and moist.
Visit your local state park and ask for an amphibian tour from your park ranger.
Step 2: Determine the Location of your Frog Tunnel
The location of your tunnel is one of the most important aspects of this activity.
Find out which area in your community has the most amphibian/frog roadkill. It will help your frog tunnel save as many amphibians as possible.
Craft a letter to your local Fish & Wildlife Department or Sanitation Service. Ask which road has the highest number of frog or amphibian deaths in your community.
This information will be very valuable so that your frog tunnel can be as effective as possible.
Step 3: Make your Tunnel Habitable to Frogs
What can you place inside your tunnel to make it habitable to frogs? Do frogs prefer leaves or small plants in their tunnel? Should you add layers of rocks or keep the tunnel flat?
Hint: Most frogs eat insects. Your tunnel will be more attractive to frogs if the entrance and exit are populated by insects.
Step 4: Help Guide Frogs into your Tunnel
Guiding frogs to use your tunnel will increase its chance of success. Small fences, culverts or road barriers near the road will help guide frogs into your tunnel instead of crossing the road.
What other ways can you encourage frogs to use your special tunnel?
Discussion Points & Questions
- What are the frog species local to my community?
- In the fall, where do these frogs prefer to overwinter?
- In the spring, where are this frog's mating ponds?
- Which roads pose a threat to frogs during fall and spring movements?
- Where would you locate your frog tunnel?
- Is your tunnel to help frogs reach their autumn wintering grounds or spring breeding ponds?
- How many tunnels(s) would you build?
- How would you encourage frogs to use your tunnel?
- What can you place inside your tunnel to make it habitable to frogs?
- How can you make the tunnel’s entrance and exit inviting to frogs?
- Can you re-use an existing tunnel to create a crossing instead of building a new one from scratch?
- Are there any abandoned or unused small tunnels that can be repurposed for frogs?
- Planting native plants at your tunnel entrance and exit will attract beneficial insects. Since frogs eat insects, these native plants will make your tunnel more attractive to frogs.
- More than one tunnel will help save more frogs! Your frog tunnel design may wish to have multiple tunnels, as guiding frogs into your tunnel will be a challenge.
- Both ends of the tunnel should stay open as wide as possible for easy access and exit. If one side is hidden, frogs will not find it. The exit should not be too narrow as predators will lurch and prey on frogs as they leave the tunnel.
- Guiding frogs into your tunnel is key! Small fences or raised structures along the road will block frogs from accessing it. These barriers may in turn help guide frogs to your tunnel.
- Ambient lighting within the tunnel helps attract frogs through the tunnel. If the tunnel is completely dark, frogs will hesitate to use it.
- Using structures that already exist will increase the chance of your frog tunnel design being adopted by your town. Can a dedicated space or small structure be set aside for amphibians within an existing tunnel? This approach will cost significantly less public funds and stand a greater chance of approval.
All kinds of wildlife crossings exist to help animals cross roads and connect fragmented populations.
- Squirrel Bridge
- Turtle Tunnels
- Salamander Tunnel
- Penguin Underpass
- Wildlife Overpass
A Friendly Disclaimer
We intentionally use the word “Design” as this activity is a survey and mapping challenge. We do not recommend that students or minors build a tunnel underneath a roadway with vehicles. Such an activity should always be overseen by adults and organizations experienced with such construction.
Build a small prototype of your tunnel using recycled materials
Call your local sanitation department to find out the road with the most amphibian deaths
Share your class’s frog tunnel design with your state's Fish & Wildlife Department
Share your frog tunnel design and photos as a blog with the Nature School community