The sight of a huge whale floating upside-down might be worrisome. Is it sick or injured? According to a new study, probably not—the whale is likely a mom taking a well-deserved break from raising her calves. Southern right whales (Eubalaena australis) migrate extremely long distances—about 3,728 miles (6,000 kilometers)—between western Australia and Antarctica. While following this long journey with overhead drones, researchers noticed that some of the whales would lie upside-down at or just above the ocean surface. Upon further investigation, the team concluded that, fortunately, the whales weren’t sick. Rather, this behavior appeared to be a whale mother resting, either to prevent overheating or to get some reprieve from feeding milk to her calves. The team published its results in a recent paper for Mammalian Biology. “To our knowledge, no other large whale has been recorded resting this way,” study co-authors Kate Sprogis, Renae van Noort, and Fredrik Christiansen wrote in a column for The Conversation. Sprogis and van Noort are marine biologists at the University of Western Australia, whereas Christiansen is a marine biologist at Aarhus University in Denmark. Upside-down moms When the team noticed upside-down whales, its first instinct was to identify who was lying this way—was there a particular sex or age group that preferred this position? From their observations, the researchers realized that only mothers with newborn calves (and one mother in the late stages of pregnancy) were resting upside down.