Monitoring Movements through the Tunnel

We chose two methods to find out whether amphibians are using the new tunnel as a safe passage under the highway.

Method 1:

We marked amphibians that we caught in the forest on each side of the highway. We gave animals on the west side a different colour than the ones on the east side. We set up traps at each end of the tunnel, to intercept some of the amphibians as they exited, while not blocking others from entering in the opposite direction. We caught the ones that were intercepted and checked to see if they were marked on the opposite side of the road. If so, we gave them a second mark so we wouldn’t count them twice if we happened to catch them again.

Trap and fence to intercept amphibians exiting the tunnel in the foreground

Juvenile Red-legged Frog with foot marked in two colours after moving through tunnel

Results so far: 

We caught 22 marked frogs and salamanders on the opposite side of the highway after they crossed through the tunnel. That’s exciting, but on closer examination we realize it’s a relatively low percentage of the total number we marked – over 380. One explanation is that lots of marked amphibians may have avoided our tunnel traps. Another is that they may have decided not to cross through the tunnel.

We also caught lots of unmarked amphibians, but we're not sure if they came from the opposite side, or turned away from the tunnel entrance on the same side. Our second monitoring method will help us decide how many amphibians actually moved through and which explanation about the marked ones is true.

Method 2: 

We set up a remote camera to photograph animals inside the tunnel. This is more labour intensive than you’d think. Amphibians are cold-blooded so they don’t trigger infrared camera sensors in the same way that people, bears or mice would. We had to set the cameras to take a picture every minute and now we’re looking through thousands of images.

Results so far: 

We still have more images to look at before we can compare numbers crossing each night with the numbers caught in traps, but, so far, we have photographed 30 different frogs and salamanders in the tunnel over 50 nights. Here are some of the images taken in the tunnel. Look carefully for the frogs & salamanders… they are little.

We also saw some warm-blooded animals moving through…. 

Whoa, how'd you fit in there!

We plan to continue monitoring when the weather warms up this spring. Stay tuned for more results as they become available.

In the meantime, for more information on monitoring salamanders using tunnels, check out this interesting publication of research done at Waterton Lakes National Park.