Rory Wilson recalls some nervous waterbirds. "I've seen pelicans in Galapagos, in the port," the Swansea University biologist says. One set of birds was standing by the fish-gutting area and waiting for scraps, while another group stood out of the fray in some nearby bushes. Although both sets of pelicans acted the same, a closer look at the birds waiting for fish scraps revealed that they were quaking slightly. The tips of their wings trembled. Wilson thinks the tremor in the pelicans' wings revealed their stress in that moment. He also believes that studying similarly small movements in all kinds of animals could give scientists new insights into their lives and health. To show how this might work, Wilson and his colleagues put pocket-sized accelerometers on three very different animals: humans, elephants, and cockroaches. It's popular for scientists to track animals' large-scale movements—GPS devices and motion sensors have followed the migrations of birds and giant crabs and found the ideal fatness for elephant seals, for example. But Wilson wasn't interested in where animals were going. Instead, he wanted to know how their small-scale movements revealed their emotions or other internal states. For starters, the researchers compared two groups of humans. One group had used ecstasy (MDMA) in the past; the other had never taken the drug. Accelerometers were taped to subjects' wrists. When researchers asked the subjects to hold their arms horizontally out to their sides, the accelerometers captured small tremors in their arms. The data showed a significant difference between the two groups of people, with drug users wobbling a little more. Wilson thinks that in the future, doctors might be able to use accelerometers to monitor epileptic patients and warn when a seizure is coming. Accelerometers could also tell doctors when diabetics are experiencing a sugar low. Or they could monitor long-term health—tracking symptoms of depression, how well a person is sleeping at night, or whether someone's arthritis medication is working. Next the researchers looked at elephants, using accelerometers on neck collars to measure the movements of two animals. As the elephants walked around, an observer noted whether they were moving for a "positive" or "negative" reason. Positive movement meant walking toward something desirable—maybe some food, or a nice pile of mud to wallow in. Being chased away by a dominant herd member, on the other hand, was negative movement. When the researchers combined this information with the 3D accelerometer data, they found a significant difference in how elephants moved their bodies during positive and negative states. Finally, they looked at diseased cockroaches. The scientists stuck accelerometers on roaches' backs and infected half of them with a fungus. Then they watched the roaches run around for several days. They saw that as the fungal infection got worse, the cockroaches lost "dynamism" in their movement—essentially, the spring in their step. No matter the species, researchers found a way to judge its internal state by tracking subtle changes in its body movement. They could measure differences between sick insects and healthy ones, elephants having a good and a bad day, and human drug users and non-users. Wilson thinks one of the most exciting potential uses for accelerometers is to study animal stress, especially in places where animals have to interact with humans. For example, how much stress do animals experience when new roads cut through their habitats? How stressed are they by new buildings, or just the presence of humans and our vehicles nearby? Even though the movements being measured are small, Wilson says, "the potential ramifications are enormous." Image: by Madeleine Holland (via Flickr)
Wilson, R., Grundy, E., Massy, R., Soltis, J., Tysse, B., Holton, M., Cai, Y., Parrott, A., Downey, L., Qasem, L., & Butt, T. (2014). Wild state secrets: ultra-sensitive measurement of micro-movement can reveal internal processes in animals Frontiers in Ecology and the Environment, 12 (10), 582-587 DOI: 10.1890/140068
