Not all Southern Hemisphere humpback whales migrate toward the equator at the end of the antarctic summer, scientists say; some choose to stay through winter. Researchers at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Germany said the discovery is based on underwater recordings from an antarctic acoustic observatory that regularly records sounds of humpback whales even in the antarctic winter months. Marine biologist Ilse Van Opzeeland said the live stream from the observatory in April resounded with the calls of humpback whales at a time when the marine mammals should long have been swimming 4,300 miles further away in the warmer waters off Africa. \"I was totally surprised, because the textbook-opinion until that day was that humpback whales migrate to antarctic waters only in the austral summer months,\" she said. Scientists said they had believed even in the summer humpbacks would only be feeding on krill in the ice-free regions around 60 degrees south latitude, but the observatory detected the whale sounds at 70 degrees south, much further south than hitherto known feeding grounds. \"With this in mind, hearing the animals on a winter morning near our observatory was a double surprise,\" Van Opzeeland said. She said it was possible the calls are produced by young whale cows that are not yet pregnant and skip the long, energy-costly migration to Africa\'s coastal waters. \"A humpback whale-female loses up to 65 percent of her body weight when giving birth to and suckling a calf,\" she said. \"With this in mind, it appears energetically advantageous, from viewpoint of the young whale cows, to remain in antarctic waters during winter.\"