Blue whales – the largest animal on Earth – sing at different times of the day depending on the season, according to a new study.
US experts have recorded both individual whales and their larger populations in the Northeast Pacific, using underwater markers and microphones called “hydrophones”.
During the summer feeding season, when feasting on krill, blue whales mainly sing at night, according to the team at the Monterey Bay Aquarium Research Institute (MBARI).
But as they prepare to migrate to their breeding grounds for the winter, this pattern reverses and the whales sing during the day.
Further analysis of five years of blue whale audio could reveal new information about blue whale migration to help track the endangered creature.
Each year, blue whales undertake a 4,000-mile migratory journey, which is among the longest of any species in the world.
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The blue whale is the largest known animal to ever exist, measuring 98 feet long. Blue whales have distinct breeding and feeding seasons, separated by a long migration
The results of the study have been described as a “happy accident” after the team noticed patterns in their audio data about whales.
“Originally, we wanted to try to characterize the seasonal pattern of their presence and the different types of sounds they make,” said study author William Oestreich at Stanford University.
“But as we started to dig into the data analysis, we noticed this dramatic separation of song production during the day versus the night.
In 2015, researchers put down their underwater microphone 18 miles off Monterey Bay, 3,000 feet (900 meters) below sea level, to capture whale song.
“We found that during their feeding season, whales tended to eat during the day and sing at night, but after deciding to start their migration, they reversed this pattern,” said the author of the ‘William Oestreich study at Stanford University.
WHAT IS THE BLUE WHALE?
The blue whale is a critically endangered marine mammal.
It is the largest known animal that has ever existed.
It reaches a maximum length of 98 feet – the same length as two and a half London buses.
They were hunted almost to extinction by whaling until the International Whaling Commission banned all blue whale hunting in 1967.
‘[They] started producing songs mostly during the day, what we call an acoustic signature of the migration. ‘
The blue whale is the largest known animal to ever exist, reaching a confirmed maximum length of 98 feet (29.9 meters).
Blue whales move to the poles in the spring to take advantage of the high production of zooplankton that occurs there in the summer, then return to the equator in early winter.
They feed by filtering huge volumes of seawater through their baleen, which hang from the roof of the mouth and work like a sieve to catch zooplankton – mostly small crustaceans called krill.
For the whales examined in this study, foraging takes place off the west coast of North America in the summer, after which they swim hundreds to thousands of kilometers to the Pacific coast of Central America. to breed in winter.
During the foraging season, they gorge themselves on krill, up to 6 tonnes per day, to swell and survive, giving them the energy they need to migrate.
“You can imagine that the amount of energy needed to make this trip is quite large,” Oestreich said.
“This is compounded by the fact that they are the largest animal to ever live on Earth, which makes the timing and intensity of their feeding season critical for their survival.”
The migration of the blue whale extends from the west coast of North America to Central America to breed in winter. Blue whales return to the poles in the spring to take advantage of the high production of zooplankton for food
Blue whales are also among the loudest animals on the planet, emitting a series of pulses, whines and whines.
Despite the vastness of blue whales, scientists know very little about how they respond to changes in the ecosystem and food supply from year to year.
To capture the whales singing solo and in chorus, the researchers used two advanced recording technologies: a hydrophone and tags placed on individual whales.
In 2015, MBARI landed its hydrophone 18 miles off the coast of Monterey, 3,000 feet (900 meters) below sea level.
The hydrophone is connected to a wired underwater observatory, which provides it with electricity and communications.
Photo shows a blue whale with a visible data logging tag placed on its back in Monterey Bay, California
“The hydrophone fits in your hand – it’s a small instrument that produces big data, about two terabytes per month,” Ryan said.
Whale song wavelengths in hydrophone data revealed a distinct change over several months.
In the five years of data, the whale chorus was strongest around October and November, and chants occurred more at night.
After each annual peak of song activity, as the whales began to leave for warmer waters, song became a more diurnal activity.
“What we’ve measured hundreds of miles is actually a real behavioral signal, which represents the behavior of many different whales,” Oestreich said.
“As an environmentalist, it’s very exciting to see so many whales, simultaneously, using just one instrument.”
Sound is a vital mode of communication in the ocean environment, especially over long distances.
This photo shows first author William Oestreich observing whales off Monterey Bay, California.
Emitting sound waves helps blue whales detect objects when they are reflected back to them – a process called echo-localization.
“Light, or any sort of visual cue, is often not as effective in the ocean as it is on land,” Oestreich said.
“So many marine organisms use sound for a variety of purposes, including communicating and targeting food by echolocation.”
Oestreich and his colleagues are not the first researchers to notice whale songs at different times of the day.
However, this is the first time that these differences have been linked to a larger pattern of their life cycle when tagging and monitoring individual animals.
The researchers hope that this research, published in the journal Current biology, can help monitor and protect populations of the blue whale, which is listed as “endangered” by the IUCN Red List.
In April, the British Antarctic Survey reported that 55 blue whales had been sighted or recorded over the past year.
The government-backed organization has studied the movements of whales in the waters surrounding South Georgia Island in the South Atlantic Ocean.
South Georgia was once abundant with whale activity before hunting drove the animals to extinction, but populations may be on the verge of fully recovering around the island.
THE SONG OF THE WHALE EXPLAINED
For a long time, it was believed that whales sang only for mating purposes.
But some experts suggest that songs also help mammals explore their surroundings.
Researchers have recorded humpback whales changing their calls as they move to new pastures to match the songs of others around them.
Learning these songs can help whales find their way around and regroup better when in unfamiliar waters.
Researchers have recorded humpback whales changing their calls as they move to new pastures in order to match the songs of others around them (file photo)
It is difficult for scientists to study whale song because shy beasts are notoriously difficult to observe and each species vocalizes differently.
Humpback whales sing using voice box folds that vibrate at low frequencies when air is pushed over them.
It has been suggested that they have special air sacs adjacent to these vocal cords that connect to the lungs.
These allow whales to pass air between their lungs, sacs and vocal cords without losing any of their precious air supply.