Pauli and his colleagues captured 10 brown-throated sloths. They are a three-toed species. The scientists also collected 12 Hoffmann’s sloths, which are a two-toed type. All came from a study site in northeastern Costa Rica. Here, the sloths live among a variety of habitats. These range from pristine forest and cacao (Ka-KOW) agroforest to fields of banana and pineapple.“It’s really a quilt of different habitat types,” Pauli says. And it’s one that allowed the researchers not only to study many habitats at once but also to more easily capture and track sloths than if they were in dense jungle.Many elements come in more than one form, or isotope (EYE-so-toap). The researchers injected the sloths with water labeled with specific isotopes of oxygen and hydrogen, then released the animals back to the wild. After 7 to 10 days, the scientists again captured the sloths and sampled their blood. By seeing how much of the isotope labels remained, they could calculate the sloths’ field metabolic rate. This is the energy that an organism uses throughout the day.The field metabolic rate for the three-toed sloths was 31 percent lower than that for two-toed sloths. It also was lower than that found in any mammal that was not hibernating. The researchers reported this May 25 in the American Naturalist.