How do you find an animal the size of a house cat in the middle of a dense, mountainous forest?
By listening for the sound of a beep.
The beep will come from radio collars we have fitted on seven spotted skunks here in the HJ Andrews Forest. First used on grizzly bears in the 1960s, very high frequency (VHF) radio collars have been the go-to tool for biologists tracking the daily habits of wildlife ever since.
For our study, we want to find out where skunks move throughout the day and how big of a space they need to make a home territory. Do they like lots of open space, or do they like to hide in dense forest where there’s a lot of logs and ferns to hide under? Do they rest in giant old-growth trees or stumps of trees cut down years ago?
The radio-collars will help provide those answers and more. While we get a lot of information about where skunks are and aren’t found from our game cameras (see our blog entry “The Secrets of Camera Trapping”), they only give us a big picture answer to our questions. One drawback to using game cameras occurs when the camera doesn’t take photos. It’s hard to know if an empty set of photos means there aren’t any animals where the camera is, or if they are around but didn’t get close to the camera (wildlife researchers call this “detection probability.”) We also can’t tell individual skunks apart on camera, and only get a snapshot of what the skunk is doing in that moment. Only by following several individuals over a long time can we answer more detailed questions, like how often they visit certain spots or how far they travel, which are important to understanding how skunks live and why they make the choices they do.
When we capture the skunks (see our last blog entry “Rain, Rain, Here to Stay”), we place the collar around the skunk’s neck, which weighs 20 grams, no more than a child’s play wristwatch. Each collar has a battery and a transmitter inside it that puts out a radio signal. This signal frequency is unique to each animal, much like how each radio station has its own channel.
A few days after the skunk is captured, we check in on it by listening for the radio signal. A special device called a receiver, which is like the radio in your car, picks up the radio signals from the collars. We tune it a lot like you flip through radio stations while driving. We even have an antenna attached to our receiver to help us pick up the right “skunk station.”
When our receiver emits a chirpy beep, we have picked up a radio signal. The skunk is close by, and we need to find out which direction it is in. We figure this out with the antenna, which will make the receiver beep loudest when pointed directly at the skunk. Once we find this spot, we take note of where that direction is with a compass.
From here, we do one of two things. We can repeat this process several times at different places and draw the directions we heard the signal from on a map. This constructs a triangle of where we think the animal is. The process, called triangulation, is like a technique a navigator uses to find out where he or she is on a map. We can also follow the beep of the radio signal from our receiver until we see the skunk. This is a lot like playing Hot-Versus-Cold in the middle of the forest, and the receiver tells us if we are getting closer or further away by changing its volume.
Not only is tracking with radio collars a challenging and rewarding way to look for wildlife, the technology still reveals unknown behaviors and important pathways animals use to move long distances. What biologists and wildlife conservationists learn from radio tracking can have major impact on which lands need to be protected for a species’ survival, as well as reveal new details about a species’ behavior that would otherwise remain undiscovered. Because so little is known about our spotted friends, our collars are sure to help us discover what they need to survive in the forest.
Check back here for updates on the travelling tales of our skunks! Find out what we learn from listening to Skunk Radio.