"This is science Americans. Sixty seconds science. I'm Christopher Dodd Yata. Blue whales are the largest animals ever to exist on earth, but they're still tough to track because they live underwater where we can't easily see them and often in remote areas like the Southern Ocean. But the whales songs can travel hundreds of kilometers underwater. So scientists often listen for them instead. By the way, that sped up ten times. He can hear it. Over the years. These eavesdropping biologists have noticed a mysterious trend that certain blue whale calls are gradually lowering in pitch over time. For example. Here's a call from two thousand two followed by one from twenty seventeen. It has been observed for many the way today Shen one wide so woman as to would white explanation. Emmanuel Lewa is a bio acoustic at the university of New South Wales in Australia. She did the work at the university of breast and France her team confirmed the phenomenon holds true for populations of blue whales in the southern Indian Ocean to and they suggest one reason may be that whale numbers have rebounded from the days of captain Ahab. More whales means individuals don't have to shout his loud to be heard by other whales, and because of an anatomical peculiarity in the way, Wales sing the softer. They sing the lower the pitch. The scientists have another theory to which may be acting in concert with the first which is that whales are singing more softly, and therefore more deeply because increasingly acidic ocean waters carry their calls further the full right up is in the journal of geophysical research oceans, low Wigner team noticed one other short term trend. That southern blue whales songs actually, get higher in pitch during the austral summer perhaps in an effort to be heard over cracking icebergs like when you put some ice cube in your drink. You will your crack? So it's the same one is bed. So it's will be really loud and you yards across a new Shannon basing to solve these mysteries. More definitively. Scientists say will need to keep listening and monitor the changing chemical and Kucic properties of the oceans to see which of these ideas are borne out and which of them don't hold water. Thanks for listening for scientific American sixty seconds science. I'm Christopher Don. Yata?"