Published: November 2005
Following the Stealth Hunter
Six months on the trail of ocelots yields just six quick sightings. Why are these shy predators so tough to spot?
By Chris Carroll
National Geographic Staff

It's the end of the dry season in Panama, and the jungle is parched. On a forest floor thickly littered with dead leaves, photographer Christian Ziegler stands perfectly still, listening intently to the beeping of the radio-tracking device his assistant is operating.

Nearby, perhaps only 30 feet away, an ocelot is on the move, according to the receiver's constantly shifting pattern of beeps. Yet despite the crackling ground cover and the fact that this feline predator can be as large as a medium-size dog, Ziegler can't see it or hear its steps. His human senses have been foiled by the cat, whose spotted coat helps it blend into the dappled light of the forest. The receiver gradually goes quiet as the ocelot departs, unseen and unheard.

Ziegler later comments, with mixed frustration and awe, "In six months I probably saw them with my own eyes only six times usually for a split second as they flitted away."

The stealth of this species (Leopardus pardalis) and the heavy forest cover in which it often lives its range spanning the Americas from south of the Amazon Basin north to the Rio Grande Valley of Texas make it tough on scientists trying to observe ocelots in the wild. "You can' sit in the Land Rover with binoculars like you're watching a lion stalk on a savanna," says Roland Kays, curator of mammals at the New York State Museum. He is studying interactions between the ocelots of Panama's Barro Colorado Island (BCI) and the cat's favorite prey a seven-pound rodent called the agouti.

Here on BCI, Kays and Martin Wikelski of Princeton University are testing a groundbreaking animal-tracking system called the Automated Radio Telemetry System, or ARTS. With funding from the Levinson Family Foundation and the National Science Foundation, the system was installed by the Smithsonian Tropical Research Institute, which has run a research station on BCI for 82 years. Ocelots and agoutis were the first species to put ARTS through its paces.

Traditional wildlife radiotelemetry requires several researchers to scramble about with receivers to triangulate the position of an animal that had previously been trapped and collared with a transmitter. In contrast, ARTS consists of seven permanent radio towers positioned across the island. They pick up and relay signals to computers that constantly monitor dozens of animals. "You can gather more data in one week than you can in years of traditional telemetry," says Kays.

If he wants to know the daily activity schedules of his subjects (as well as of other species the system now tracks, such as sloths, monkeys, and opossums), he can simply scan the computer. One program produces a graphic that shows when the animals are active. This allows researchers to keep track as ocelots rouse themselves, typically around 6 p.m., to go on a prowl that will likely continue until morning. ARTS also constantly maps the locations of the cats, which has helped scientists learn that the average home range of a male BCI ocelot is 1.4 square miles; for females, it's about 0.6 square miles. This spatial monitoring becomes especially exciting, and scientifically illuminating, in the rare case when two collared animals meet and interact.

Useful as it is, "technology can't replace fieldwork," Kays says. He and his colleagues also use traditional methods like collecting scat and searching for paw prints. Their goal: to learn more about the importance of predators to ecosystem health. For instance, if ocelots were to become extinct on BCI, unchecked rat or agouti populations that devour seeds could wipe out some plant species.

Ocelots do face threats from poaching and habitat destruction. But happily, now that hunting the cats is illegal in most of their range, there's little danger the 1.5 million to 3 million ocelots living in the Americas will disappear anytime soon. In many parts of the tropics, hunting has decimated populations of jaguars and pumas, the Western Hemisphere's largest feline predators, raising ocelots' status a notch in the ecosystem big shoes to fill for the forest cats.

"They may now be the dominant predators in many areas across the tropics," Kays says. "To what extent can they play the balancing role of large predators? This is a question we want to answer."