What is a Camera Trap?
Imagine walking through a section of undisturbed forest in the Himalaya Mountains. You find tracks and claw marks suggesting a bear can’t be too far away. But how do you prove it? Is it a Himalayan black bear or an Asiatic brown bear? How can you find out?
You could set some type of animal trap, but that might hurt the animal. Searching on foot could take hours, or days! Wild animals naturally avoid people. They will move away within seconds of hearing, seeing, or smelling them. And finally, in a place like Nepal, the number of animals living in a section of forest, called the animal density, is low.
To get around these problems, wildlife biologists developed a scientific method called “camera photo trapping.” The idea behind this method is very simple: use a camera outfitted with a motion detector to capture an animal image. These special cameras are placed near animal trails, favorite feeding or watering grounds, or where evidence of the animal has been found. They can be left in place for days to weeks, eliminating the need for people to sit by and watch. When the animal walks by the camera, a picture is taken automatically. Camera traps are used all over the world to study a variety of species.
How do Camera Traps work?
The camera itself is very simple: a regular film or digital camera with a flash. The most complicated part of the camera trap is the motion-detector sensor. These sensors use a type of energy technology called infrared. The sensor sends a narrow beam of energy out into the air in a straight line. When this beam is disrupted, it triggers the camera to take a picture. The body heat of an animal, or a person, will disrupt the beam.
The camera, sensor, and battery are placed inside a hard plastic box for protection. Monkeys, for example, can easily take the traps apart! The boxes are painted in camouflage colors to prevent animals and people from noticing them.
It is important to carefully plan where to place the camera trap. Wildlife biologists first look for animal sign, physical evidence of the animal. These may include tracks, animal dung (called scat), burrows, and trails, places where the animal eats, rests, or sharpens its claws. Scientists also rely on anecdotal evidence, stories told by people living nearby about animals they may have seen or heard. The evidence is carefully considered. Animal trails and feeding sites seem to work best.
The camera must be positioned unobtrusively near the animal sign. Trees or rocks work well to anchor the camera. The goal is to aim the camera in such a way that it provides a wide field of view, so it captures most or all of the animal, rather than just the back or feet. Even so, it’s impossible to set the camera for all possible species. For example, if a very short animal like a leopard cat triggers the sensor on a camera trap set to find a tall animal like a Himalayan tahr, the result might be an empty image.
When positioning the cameras, wildlife biologists use their best judgment, based upon the animal they are most interested in capturing with the trap. Sometimes, they use a natural chemical called animal lure, placed on the ground to attract the animal. This works particularly well for carnivores who hunt by smell. They also leave the cameras set up for several days to weeks, even months at a time. The longer the time period, the more likely they are to capture interesting images. And that’s the most exciting part – getting a great picture.
What do Camera Trap pictures look like?
The pictures obtained with camera traps do not look like regular photographs. They may be very bright or very dark depending on the time of day. Usually they are blurry since the cameras don’t use auto focus. The sound of the tiny motor can scare animals away. Most animals can even hear the shutter open. Prey animals like musk deer and muntjac may jump away at the noise, out of the picture frame. Predator animals like leopards tend to me more curious. Often, these cats will turn in the direction of the camera when they hear the shutter click.
The distance between the animal and the camera also makes a big difference. If the animal is far away, the photograph will usually capture the entire animal. It may even show more than one, like a pack of dholes. But if the animal is close to the camera, the photograph may show only a part of the animal. This can make it difficult, or impossible, to identify the species. For example, the photograph may show part of an ear, or just the muzzle of an animal. Or, the animal may brush by a piece of grass or small tree that sets the camera off. These pictures have no animals in them at all.
Sometimes, camera trap photos raise more questions than answers. Maybe an animal not thought to live in a particular area shows up in the photos. Scientists will then want to know why. Maybe the animal looks like a new species. Or, maybe its behavior looks unusual. For example, a black bear may be standing on its hind legs reaching for berries. The picture may be dark and fuzzy. Could it be an entirely different animal? Could it be the yeti? Scientists will want to know more. This is an important part of the scientific process: answering one question often leads to asking another. The result of good science leads to new discoveries and new investigations.
Can you make a camera trap yourself?
Before camera photo traps became commercially available, scientists made their own. The components include:
- Camera – 35 mm film with flash or digital
- Plastic box
- Battery
- Infrared (motion detector) sensor
- Laser beam
- Straps to attach the camera to a tree
- Film or memory card
The box that houses and protects the camera must be big enough for a battery, suitable to power the camera for several months. The sensor is positioned just below the lens of the camera, through a second hole in the plastic box, so that both aim in the same direction. Most cameras have a laser beam attached to the sensor which can be turned on while the scientist positions the camera. This helps ensure it is pointed in the right direction, at the appropriate level and angle.
What can go wrong with camera traps?
Since most pictures are taken in dim light or at night, a flash unit is essential in order to see anything in the image. Animals, however, learn quickly about these flashing boxes and many will stop coming back to the same site. Wildlife biologists often move the cameras to avoid this problem.
Heat, humidity, and cold can affect how well the cameras function. The batteries can fail. People, or other animals, can disrupt the traps. Elephants will pull the camera right off a branch, or trample a tree entirely. Poachers, and sometimes even legal hunters, will often move or remove the cameras. Camera traps return images of humans quite often.
Camera traps of the future
Scientists are continually looking for ways to build a better camera trap and collect even better information. For example, the commercially available digital media camera traps can store many more images than the standard roll of 36 pictures for a 35 mm camera. Digital video camera photo traps have also recently been developed. These work especially well to capture images of animals that repeatedly return to a feeding site or watering hole. In some places where wireless technology is available, webcams being used to continuously monitor such active areas. Anyone could probably set up a webcam in your own backyard and catch some pretty interesting late-night animal action!
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