"Song is a loud broadcast signal and two singers singing at the same time is bound to be confusing to the receiver," Dunlop speculated. "If he's trying to attract a female, but doesn't want his signal confused with another singer in the area, then using song units in this case might be the way forward."
She thinks one reason whales are so vocal is because sound travels better in water than light, and so sight is less useful to whales than hearing.
Christopher Clark, director of the Bioacoustics Research Program at Cornell University, conducted a similar study on right whales.
He pointed out the irony that just as researchers are gaining a better understanding of whale vocalizations, humans are creating so much ocean noise — through shipping, oil and gas exploration, recreational traffic and more — that we often prevent whales from communicating.
"Many whales have very traditional feeding grounds and their migratory routes occur along shallow coastlines, which are now some of the noisiest, most heavily impacted habitats," he said.
"The ocean area over which a whale can communicate and listen today has shriveled down to a small fraction of what it was less than a century ago."
