(CN) — Scientists have discovered blue whales sing a little differently according to their migration patterns, during the day in summer feeding season and at night in the winter breeding season, filling in some important blanks in the study of whale song patterns.
Details of this study are published Thursday in the journal Current Biology, where the authors discuss their findings on the world’s largest animal.
"We found that during their feeding season, whales tended to eat during the day and sing at night, but after they had decided to begin their migration, they inverted this pattern and started to produce song primarily in the day, what we refer to as an acoustic signature of migration," said lead author William Oestreich, a doctoral candidate in biology at Stanford University, in a statement accompanying the study.
Blue whales grow to the length of three school buses and have been found to be as heavy as 15 of them, as the ocean’s size and lack of gravity allows them to grow unhindered. Like most whales, these behemoths usually travel alone or in pairs unless they’re on their way to migrate. They’re also slow, normally only traveling at about 5 miles per hour, but can reach speeds of up to 20 miles per hour when prompted.
These whales travel great distances in between the seasons, heading to the west coast of North America in the summer to feed on krill and then to the Pacific coast of Central America in the winter to mate. These journeys can be thousands of miles so feeding in the summer is vital for them to make it through the winter. They can consume up to 6 tons of krill a day by opening their massive jaws to swallow large swarms of the organisms, filtering out water and other debris.
"You can imagine the amount of energy required to make that journey is pretty great," Oestreich said. "That's compounded by the fact that they're the largest animal ever to live on Earth. So it makes the timing and intensity of their feeding season critical for their survival."
In addition to being the largest animal — and among one of the longest living — they are also some of the loudest. Their sounds consist of low moans, groans and pulses which can be heard by other blue whales from hundreds of miles away. Along with the obvious purpose of communication, it’s suspected they can sonar-navigate through dark waters with this ability.
While the study’s authors were searching through years of collected blue whale sound data for seasonal patterns, they accidentally found the creature’s sounds correlate with its migration schedules.
The team had been analyzing data recorded by the Monterey Bay Aquarium Research Institute, which has been collecting the sounds from a whale population near California for the past five years. The marine biologists tagged and tracked members from this population and got a good look at their behaviors over time.
"We were originally interested in trying to characterize the seasonal pattern of their presence and different types of sounds that they make, but as we started to dig into the data analysis, we noticed this dramatic separation of the song production during the daytime versus the nighttime," Oestreich said.
Although not the first time whales have been found to sing in daily patterns, the team’s findings became significant when compared to the data collected from the tags. The researchers saw how this phenomenon relates to the rest of the whale’s lives. With the data from the tags, they learned how these patterns changed based on the creature’s breeding and feeding schedules.
"This is something that's been described before in blue whales, but in some studies, they report the day/night difference and in others, there's no differences. So there's this discrepancy in the literature about when and why it happens," said Oestreich.
"An unexpected part of this work is that whale songs are typically thought of only in a mating and reproductive context," Oestreich added, noting how his findings help in breaking away from the idea that whale sounds are strictly mating calls. "We don't dispute that, but it's interesting that there's this kind of secondary utility of song in terms of detecting foraging or migration based on the time of day the sounds are being produced."
Unfortunately, blue whales are critically endangered due to human activity. Global bans on commercial whaling have helped in reducing our threat, but the animals still face risks from ship strikes, pollution, and a population decline of their food sources. The authors hope their findings can contribute to protecting and conserving the blue whale population.
"A lot of folks are interested in this kind of work in an applied sense — how this can help the management of marine habitats and mitigating risks of ship strikes on these animals in crowded shipping lanes," Oestreich said. "This certainly isn't a silver bullet for that, but you could see it contributing to it."