Field biologists are increasingly turning to camera traps to collect data. The set-up is really simple: when an animal passes in front of a camera, an infrared sensor becomes activated, and the camera silently snaps a photo. Sometimes - especially for camera traps designed to detect nocturnal species - an infrared flash, invisible to most mammals and birds, is used.

The photographs generated from camera traps can then provide researchers with far more data than they would be able to collect themselves with more traditional field observations. Often, this allows them to generate photographic evidence of a species' natural behaviors without the confounding effects of direct human observation. It allows them to collect data continuously, throughout the day and night. And a camera trap can help researchers collect evidence of rare species or rare behaviors, as was demonstrated last week when a camera trap captured a golden eagle preying upon a sika deer. Or they could help researchers come face-to-face with an animal that might otherwise be dangerous or harmful. An array of camera traps is also more cost efficient than paying an army of field assistants to observe animal behavio or to conduct a census.

Camera traps are also far less invasive than most other forms of wildlife data collection, since critters don't need to be trapped and released. And their presence is far less stressful for most animals compared with human observation.

Take the jaguar. The third largest cat in the world after tigers and lions, jaguars (Panthera onca) are nocturnal, solitary cats. Females' territories can range from twenty-five to forty square kilometers, and males can roam areas twice as large. Due to primarily to habitat loss and to conflict with farmers, jaguar populations are declining; they're considered "near threatened" by the IUCN. Oh, and a mature jaguar's jaws are capable of biting down with two thousand pounds of force, the strongest of any cat. It subdues its prey in an ambush attack by biting down on the skull, its massive teeth puncturing the brain adjacent to each ear.

Put together, this makes jaguars well suited for for camera trap research. Still, human observers can do things like change the direction they're looking. Cameras generally can't. So biologists like Miguel Ordeñana try to hedge their bets and optimize the probability that an animal of interest will come by and trigger the camera's shutter.

Ordeñana is a biologist with the Natural History Museum of Los Angeles. He's an expert on camera traps, and when he's not using them to understand the mountain lions who make their homes in the mountains of Los Angeles, he conducts field research on jaguars in Nicaragua.

And the best way to convince a jaguar to trigger a camera trap? Calvin Klein Obsession for Men. Seriously.

According to Ordeñana, a Bronx Zoo researcher once tried a bunch of different scents and discovered that jaguars really liked the Calvin Klein cologne. A researcher might spray some of the cologne on a tree branch that sits within the camera's field of view.

What's so special about this particular scent mixture? "It has civetone and it has vanilla extract," he says. Civetone is a chemical compound derived from the scent glands of civets, smallish nocturnal cat-like critters native to the Asian and African tropics, and it's one of the world's oldest perfume ingredients. "What we think is that the civetone resembles some sort of territorial marking to the jaguar, and so it responds by rubbing its own scent on it," he explained to me. And the vanilla might set off the cats' curiosity response. No matter which compound is responsible for jaguars' interest - or both - the key is that the scent gets them to stick around long enough to activate the camera's shutter.

I asked Miguel if he avoids wearing Calvin Klein Obsession for Men while doing field work in Nicaragua. "I don't really care, because the chances of me running into a jaguar are so slim." Which, after all, is why he uses the camera traps in the first place.

Still, you probably wouldn't want to wear the cologne and then take a nap, alone, at night, in the jungle. Then again, you probably wouldn't want to do that anyway.

Images: Header image via Bjørn Christian Tørrissen/Wikimedia Commons. Camera trap photos via Paso Pacifico, used with permission.
