Caught in the trap! Remote cameras with electronic beams are the newest tools for biologists investigating mysteries in the wild

International Wildlife, Nov-Dec, 1997 by Fiona Sunquist

Despite the glitches, remotely triggered cameras are becoming an increasingly useful tool for researchers trying to answer a variety of practical questions. For Steve Humphrey, dean of the College of Natural Resources at the University of Florida, the cameras were a perfect way to find out whether the highly endangered Florida panther would use underpasses to cross major highways. "Nearly half of all Florida panther deaths are from collisions with vehicles," says Humphrey. "We wanted to see if a combination of highway fencing and underpasses would allow the cats to cross I-75 without being hit." Humphrey's cameras confirmed that the underpasses--which cost more than $1 million each to construct--were used by panthers, justifying construction of additional crossings. Surprisingly, bobcats, deer, raccoons, alligators, wading birds, dogs and humans also used them, the camera traps showed. "We had great pictures of a guy illegally driving through the underpass," Humphrey says. "The photo clearly showed his license plate, so the cops used it to track him down and remind him not to drive through these things."

At the National Zoo in Washington, D.C., curator of mammals John Seidensticker needed a noninvasive way to find out how many feral cats were using the zoo grounds. Free-ranging cats can be a major problem in zoos because of disease transmission. "We assumed from tracks that there were quite a few cats coming and going, but we did not want to upset our human neighbors by ear-tagging and radio-collaring their pets," says Seidensticker wryly.

Camera traps were the perfect solution. The cats photographed themselves going in and out of many of the cages. "We found that the most popular nighttime hangout was the bald eagle's cage," Seidensticker says. Cats, raccoons, opossums and night herons also converged at the eagle cage to feed on scraps of dropped fish. "The big surprise was that we discovered there were wild gray foxes living in the heart of Washington, D.C.," adds Seidensticker.

In India, Ullas Karanth's work with tigers has made him the state-of-the-art leader in estimating animal numbers. Working with U.S. Fish and Wildlife Service biologist Jim Nichols, who specializes in statistics, Karanth continues to perfect techniques for using cameras to estimate tiger numbers. "Dense vegetation and large areas make it impossible to get a total count of all the animals in a population," explains Karanth. "The best way to estimate animal numbers is to sample, just as pollsters sample voter opinion."

For his sample, Karanth sets out as many as 15 photo stations at carefully predetermined places in the forest. Each set has two cameras, one on either side of the trail. "Individual tigers and leopards have unique coat patterns," Karanth says, "but you need to have matched photos of both sides of the animal because each side has a different pattern." Karanth does not have to photograph every tiger in the area, because the frequencies in which known tigers turn up in the photos enable the computer models to estimate what fraction of the overall population has been photographed. That, in turn, leads to an estimate of the total population.