Wild Kingdom

Tracking Ocelots, Monkeys, and More in Panama

By Doug Peterson

April 2007

Two blips on the monitor screen slowly close in on each other. They move closer and closer until all of a sudden one of the signals goes constant, while the other one continues to fluctuate.

It comes across innocuous and sterile on the monitor. But in reality, what just happened is that an ocelot killed an agouti, a rodent the size of a woodchuck. It’s all part of the largest animal radio-tracking system in the world -- the Automated Radio Telemetry System on Barro Colorado Island in Panama.

At the heart of this animal-tracking system is an antenna network designed and manufactured by Bill Cochran, a radio engineer from Champaign-Urbana. What’s more, George Swenson, a CSL professor emeritus of electrical and computer engineering, has been acting as a pro-bono consultant since the network was established.

According to Swenson, the 1,600-hectare island (6 square miles) is networked by seven tall towers, each equipped with six antennas pointing in six different directions. The system keeps track of dozens of animals simultaneously and transmits data to the Internet, where researchers can follow the animals 24/7.

Barro Colorado Island is home to a recorded 1,316 plant species, 381 bird species and 102 mammal species. As part of the Smithsonian Tropical Research Institute, it is considered one of the most intensively studied areas in the tropics.

Although the reservation on Barro Colorado Island has been around for more than 90 years, the antenna tracking system was not erected until five years ago. Martin Wikelski, a former U of I biology professor now at Princeton, recruited the services of Swenson because the CSL professor is a long-time expert in radio engineering with an active interest in wildlife. Swenson also developed some of the first radio tracking systems to study the Soviet Union’s Sputnik satellites beginning in the late 1950’s.

Actually, Swenson credits Cochran, from the Illinois Natural History Survey, with the pioneering work in automated animal tracking. Cochran, a technician working with Swenson in the late 1950’s, essentially made Champaign-Urbana the de facto birthplace for wildlife telemetry by designing the first tracking device ever used on an animal in the United States. He built a crystal oscillator into a little collar and attached it to a rabbit in Allerton Park, not far from the U of I campus.

Swenson says Cochran soon followed in the early 60’s with the first published paper on wildlife telemetry. This paper recounted their experiences in tracking a very disoriented mallard duck as it passed over their field station near Champaign several times. By happenstance, the device also picked up the respiration rate of the bird as it beat its wings -- another all-time first.

On Barro Colorado Island, the automatic telemetry system continues to evolve as they test new ways to speed up the direction finding process. Swenson says the biologists he works with are “some of the most enthusiastic users of this technology.” But they have a lot to learn about radio transmission, which is why he continues to serve as a consultant.

Biologists use the telemetry system to study how animals on the island, such as monkeys, rats and ocelots, interact with the environment and with other species. They also collect data on “death and dispersal,” something that has been lacking in many ecological models. Their tracking devices even collect physiological data such as heart rates of animals, as well as the activity rhythms of animals during both night and day.

However, biologists don’t just encounter animals on the screen. The tracking system often leads them to live encounters -- and these can be intense.

For instance, Swenson recalls when biologists fired an enormous slingshot over the branch of a tree 150 feet in the air. They used this slingshot to pull a rope over the tree branch. Then one biologist scrambled up the rope like a mountaineer scaling a cliff and proceeded to wrestle with a sloth 150 feet off the ground.

“These biologists can be pretty zealous and adventurous,” Swenson says with a bit of an understatement.

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