The invention of camera traps has changed conservation. By setting up a remote camera that takes a photo every time a creature wanders past, scientists can study wildlife without spending long, expensive days in the field. But there’s a problem: most camera traps are triggered by an animal’s heat ... so they don’t catch cold-blooded animals like reptiles and amphibians.
Clearly, the cold-blooded need a camera trap of their own, and research teams are starting to make them, at least on a small scale. One comes from the University of Vienna in Austria. Last September, Christoph Leeb, then a master’s student at the university, walked into the woods on the outskirts of the Austrian capital. Soon, he veered off the marked path and climbed down into an old trench, dug long ago probably for military use. A few steps on, he came to a small hole in the side of the trench, the entrance to a burrow where fire salamanders (Salamandra salamandra), among Europe’s most common amphibians, hibernate every winter.
Leeb doesn’t know what the inside of the burrow looks like. But he does know what goes in and out of it. That’s because his camera trap has been sitting in front of the burrow from about September to June for the past three years. This is how it works: a tripod holds a digital Canon camera (bought on eBay) above the entrance hole, facing down. A light barrier sends a constant infrared beam across the hole, like a security system in a heist movie. Using instructions from an online community, he has hacked the camera to click two photos when something crosses the infrared beam. He's also used a childhood Lego set to construct walls that encourage the salamanders to walk through the light barrier. “It was fun to play with [the Lego] again,” he says. The whole thing, whose parts cost only about €300 (around $416), is run by a car battery that provides about 40 days of power and is covered by a net to prevent debris from falling in.
Leeb’s device, which is one of a kind, is part of a project to study the fire salamander population in parts of the Vienna Woods. Fire salamanders are beautiful creatures – shiny black with spotted patterns in bright yellow, orange and even red that are unique for each individual, making it possible for Leeb to identify each one separately. The salamanders are not considered endangered, but last fall, a paper in the Proceedings of the National Academy of Sciences reported that a newly identified fungus had nearly wiped out the fire salamander population of the Netherlands. It’s related to another lethal fungus, known as the amphibian chytrid fungus or Bd, which has caused a precipitous decline in many amphibian populations around the world.
Camera traps could be part of the solution for amphibians threatened by disease because so little is known about most wild populations, including fire salamanders. Leeb was amazed by just how many fire salamanders used the burrow he studied. In the first year, his camera trap took photos of 214 individual fire salamanders, and up to 190 were in the burrow at the same time. That’s about 10 percent of the population that lives in the local catchment area, he estimates. His trap also revealed that the fire salamanders share the burrow with several other species, including newts, frogs, toads, mice and snakes. “It has to be a huge space,” he says. During the second year of monitoring, Leeb found that nearly 80 percent of the salamanders from the first year returned for hibernation.
Conservationists could make use of findings like these. For example, they could protect the fire salamander population by safeguarding large burrows from human development, since the destruction of one burrow could have an outsized effect. They could also study the consequences of large group hibernation for the spread of fungal diseases. The fire salamanders "could maybe infect each other inside this burrow," Leeb speculates.
Despite his success with salamanders, Leeb says his trap wouldn’t necessarily work for all cold-blooded animals: frogs could hop over the beam, for example. A variety of solutions may be needed. A researcher in Australia is working on expanding the range of heat-sensing camera traps. Another team in the United States is using pressure plates to trigger them with an animal’s weight. Others are simply using cameras that take photographs at regular intervals, with no triggering mechanism.
Leeb’s small investment yielded a lot of knowledge about the stealthy fire salamander. Other cold-blooded species also have a lot to gain from the spread of devices like his.
Top header image: Alexandre Roux, Flickr
