Understanding energy expenditure can help scientists understand how well animals are doing and whether they are going to be able to hunt, reproduce, and survive. By now, Wilson has used accelerometers to study all sorts of animals including sea turtles, sheep, bats, hawks, and penguins. He combines the accelerometer data with inputs from other sensors that measure temperature, magnetic force, and geolocation to understand exactly what the animal is doing and where it is. For example, the technology allows him to track penguins as they sit on their nests, get up, waddle to the ocean, and dive in. His sensors can stay on the animals for weeks, and after he retrieves the devices, Wilson can follow along as the penguins swim and dive and fish, all from thousands of miles away.
He’s gotten so good at reading the data, he can even start to understand details of the animals’ physical state. He can tell when the penguins are full of fish, for example, because that changes how they waddle. Or he can tell when a horse is starting to walk over tricky terrain. “That’s really cool stuff,” he says.
Like Chusyd, Wilson has become well-versed in figuring out how to attach accelerometers to animals and making sure the sensors will survive the data collection process. For penguins and other birds, he’ll insert special tape under their back feathers, creating a little waterproof pocket into which he encloses the device. He used magnetic and spring-based clips to attach sensors to sharks’ fins. When he studied sheep urination, he cut little holes in the wool on the animals’ rear ends, glued the sensors into their coats, and repacked the pockets with the tufts of shaved wool. For sloths, he used a harness, and for bats he used rubber cement to affix the accelerometers to their leathery skin.
For Anthony Pagano, a postdoctoral researcher who works with the US Geological Survey, accelerometers have helped illuminate the activity of polar bears living north of Alaska, providing insights that can be nearly impossible for humans to observe. “We have a lot of detailed information about changes in body mass and survival rates, but we don’t have very much information about basic movement patterns and what their basic behaviors are on the sea ice,” he says.
These bears live in extreme and remote environments. Temperatures can shift from 40 degrees below zero up to 30 degrees above zero. The polar bears are diving in and out of frigid salt water oceans, hanging out on ice floes, and tramping around on solid ground, too. Pagano ultimately had to encase the accelerometers in epoxy to make them waterproof, mounting them in an aluminum housing and bolting the whole unit to tracking collars around the bears’ necks. Like Chusyd, he also had to figure out what the patterns in the data meant by fitting bears in captivity, observing them, and then matching up those observations with the data from wild animals. Between figuring out the right bolting system and validating the data, it took Pagano a year to get ready to put the devices on bears in Alaska.
Accelerometers have some limitations. Because Pagano relies on collars to attach his sensors, he can only tag female bears; males have necks that are larger than their heads, meaning the collars will slip off. And where the sensors are placed on the animal is really important, especially if scientists want to study a particular motion or behavior. At first, Pagano wanted to find movement patterns that could identify when the bears were killing and eating seals. But because he had to attach the accelerometers to neck collars, the sensors haven’t been able to find distinct signature patterns for those killing and eating movements, because those motions are happening in other parts of the body, like the hands and feet. Maybe if the accelerometers were attached to the bears’ paws, they would be able to find that data—but there are just too many other head movements that the animals make for the sensors to pick up hunting-and-eating-specific signals.