Hydrophone on mooring listening to Bowhead whale

It is impossible to keep track of whales visually throughout the year in seasonally ice-covered polar regions. So scientists eavesdrop on bowhead whale calls using moorings with hydrophones that record their singing. Bowhead whales sing to attract mates, but their song changes throughout the season and is never identical from year to year. Scientists are studying how changes are introduced to the song and how the whales adopt these changes and end up singing the same tune. (Illustration by Jack Cook and Amy Caracappa-Qubeck, © Woods Hole Oceanographic Institution)