Biologists and physicists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, found out that not all of the Southern Hemisphere humpback whales (Megaptera novaeangliae) migrate towards the equator（赤道） at the end of the Antarctic summer. Part of the population remains in Antarctic waters throughout the entire winter. The scientists report this in a current issue of scientific journal PLOS ONE.

This surprising discovery based on underwater recordings from the Antarctic acoustic observatory PALAOA. It is located near the research base Neumayer Station III on the ice shelf and regularly records underwater sounds of humpback whales even in the austral（南方的） winter months. Sometimes even scientists need the crucial little quantum of luck to obtain new research ideas. For instance Ilse Van Opzeeland, a marine biologist and expert on large whales at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). As she unlocked the door to her office one April morning and, as usual, switched on the live stream of PALAOA, the underwater acoustic observatory, the loudspeakers suddenly resounded with the calls of humpback whales -- and this at a time during which the marine mammals should long have been swimming 7,000 kilometres 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. And even then, standing believes were that they would only be feeding on krill in the ice-free regions around 60 degrees south latitude. However, our PALAOA observatory monitors an area 70 degrees south -- so, 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," explains the scientist.

Driven by the question whether the winter-excursion of the humpback whales in the eastern Weddell Sea was a unique event, Ilse Van Opzeeland developed a procedure for the automatic detection of humpback whale calls and analysed all PALAOA recordings from 2008 and 2009 for acoustic signs of life from these animals. "Along with variable, high-frequency calls from the whales, our recordings also contain stereotyped calls that sound a bit like a moan. We concentrated on the latter in our analysis," the marine biologist tells us. "Today, we know that, in 2008, the humpback whales were present near the observatory with the exception of the months May, September and October. In the following year, they were absent only in September. Therefore, it is highly likely that humpback whales spent the entire winter in the eastern Weddell Sea during both years," says the scientist.