How Sleepy Are Sloths and Other Lessons Learned

Smithsonian scientists use radio technology to track animals in an island jungle in the middle of the Panama Canal

Three-toed sloths are among the animal species studied by Smithsonian scientists in Panama. (Oyvind Martinsen / Alamy)

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Occasionally, scientists at BCI will use GPS tags, an alternative to radio transmitters. And while they do produce a reliable location of the animal, they are expensive, don’t produce live data and are too large to use on many animals. One of the biggest breakthroughs with the radio transmitters is their size. The smallest weighs 300 milligrams—less than a third the weight of a single paper clip—and can be adhered to monarch butterflies and tiny bees. Horan, my hiking companion, has used them to track tree frogs.

ARTS has led to some surprising discoveries. A research team led by Niels Rattenborg, of the Max Planck Institute for Ornithology in Starnberg, Germany, found that sloths aren’t as slothful as originally thought. In captivity, they tend to sleep about 16 hours a day. But in the wild, they average only 9.6 hours.

Behavioral ecologist Meg Crofoot, who currently directs ARTS, uses the system to study white-faced capuchin monkeys. She has learned that when it comes to fights between social groups, victory does not depend on numbers. Regardless of group size, the monkeys closer to their home turf when the battle breaks out are more likely to win.

“ARTS is letting us get at questions that previously just haven’t been answerable using traditional field techniques,” says Crofoot.

Previously, Crofoot would have needed a small army and a massive budget to follow multiple groups of monkeys simultaneously. For this reason, very little is known about competition between social groups. But ARTS was “a new way of getting at this data.” She tagged one or two individuals in six social groups that inhabited the island and was able to trace their every movement. When she wanted to watch a group’s behavior, she could go to the lab, find out where the monkeys were and get there—a huge timesaving measure.

Of course, like any complicated system, ARTS has its kinks. According to Kays, the biggest challenges are keeping the hardware and towers functioning in such a humid environment—vegetation grows on the towers and antennas rust—and studying the sheer amount of data brought in. In the future, he hopes to find a way to automate the data analysis and increase the number of tagged animals the system can handle. Smaller transmitters, for even more insects, he says, wouldn’t hurt either.

“There are so many species that are interacting and doing interesting things,” says Kays. “Coming up with ideas for studies is the easy part.”


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