Blue Whales Sing All Day When They Migrate and All Night When They Don’t

Blue whales are the world’s largest animals, and their vocalizations are just as mighty. Their deep, low-frequency trills are strung together to compose songs loud enough to travel for hundreds of miles underwater. Scientists have spent decades trying to decipher their songs and figure out why blue whales sing — and a new study may provide more clues.

In a study published last week in Current Biology, a team of researchers discovered that during the warmer summer months, male blue whales sing at night. But when it’s time to migrate to warmer waters, they shift their timing and belt their songs during the day. This is the first instance that scientists have recorded how singing patterns vary with the whales’ feeding and mating cycles, reports Jake Buehler for Science News.

Each year, blue whales embark on 4,000-mile migrations. They spend the warm summer months feasting on krill in cooler, northern waters before traveling southward to their winter mating grounds in the tropics. An underwater microphone dropped 3,000 feet deep in Monterey Bay recorded the bay’s underwater soundscape continuously for five years, providing William Oestreich, a biological oceanographer at Stanford University and lead author on the paper, with a profound, musical dataset.

Oestreich and his team separated the daytime songs from the nighttime songs and observed a “very striking” pattern, Oestreich tells Science News.

They report that during the day, blue whales stay busy diving for krill. But when the krill disperse at night, the whales will sing for up to 12 hours on end, reports Susanne Bard for Scientific American.

In addition to listening to Monterey Bay’s whale chorus, the team tagged 15 blue whales to monitor their individual vocalizations and behaviors. They recorded around 4,000 songs, which revealed that before migration, whales sang three times more at night than during the day. But when they’ve loaded up on krilled and started swimming south, they sang three times more during the day than the night.

Scientists are still unsure why whales sing, but this study suggests that information about behavior, reproduction, and migration could be embedded in the whales’ songs, Oestreich tells Science News. If further research solidifies the connection between singing and migration, the whales’ songs could serve as an “acoustic signature of migration,” he says.

But Ana Širović, a marine biologist at Texas A&M University at Galveston who was not involved in the study, tells Science News that she is “not fully convinced that we can use switch to daytime calling as an indication of migrations.” She says she’s seen examples of whales in Southern California singing while they feed during the day and that singing whales could just be passing through the bay without having started their migration yet.

The researchers say in a press release that a deeper analysis could reveal if whale songs can be used as a forecasting tool to predict the timing of migration. If so, the results will help inform conservation practices for the federally endangered blue whales. For example, ships could be warned when the whales are migrating so they’re less likely to strike them.

“If, for example, we can detect differences in migration and foraging in response to changes in the environment, that is a really powerful and important way to keep an eye on this [endangered] species,” Jeremy Goldbogen, an assistant professor of biology at Stanford and senior author of the paper, says in the press release. “That’s economically important, ecologically important and also culturally important.”

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Rasha Aridi is a science journalist based in Richmond, Virginia. She has written for Science magazine and Science News for Students. You can find her portfolio at rashaaridi.com.