A mysterious sound emitted from the deepest part of the ocean has finally been identified as a Bryde's whale. Now, artificial intelligence is helping researchers track the elusive whale species responsible for the call. The puzzle began in 2014 when researchers recorded a sound resembling a moan followed by metallic sweeping pings over the Pacific Ocean's Mariana Trench. "Your average person would not think that it was made by an animal – they would think it was some ship or the Navy," says Ann Allen at the National Oceanic and Atmospheric Administration (NOAA). Years later, additional recordings of the sound, which researchers call a biotwang, were eventually linked to sightings of Bryde's whales (Balaenoptera brydei) near the Mariana Islands.

Recently a drone filmed a pair of whales feeding for perhaps the first time. Bryde's whales (named after the Norwegian merchant who built the first whaling stations in South Africa) reach a maximum length of over 54 feet. That's humongous, and should make it easy to observe them. The vastness of the ocean disagrees, and happily hides the whales in their vast tropical water range. Until recently, Bryde's whales had rarely been observed feeding in the wild.