Killer Whales Attacked a Blue Whale—Here's the Surprising Reason Why

A pod of orcas was seen conducting a synchronised attack on the world's largest animal, and they were probably not doing it for food.

In drone footage captured on May 18 in Monterey, California, a group of orcas is seen carrying out a coordinated attack on a blue whale.

Orcas, also known as killer whales, are known to prey on other marine mammals, including dolphins and seals. But even these fearsome predators don't stand much of a chance against a mature blue whale: The largest animal on the planet, an adult blue whale can reach up to a hundred feet long and weigh close to 200 tonnes.

In this instance, the large blue whale flipped on its side, sending up what seemed like a wall of water, and swam away at a speed that far outpaced the orcas, says marine biologist Nancy Black, who captured the event from on board a whale-watching boat.

WATCH: KILLER WHALES CHARGE BLUE WHALE (RARE DRONE FOOTAGE)

The real reason the orcas likely orchestrated an attack?

"They were probably doing it for the heck of it," says Black. "They play with [whales] like cats play with their prey. They are very playful and social."

Black runs the whale-watching business Monterey Bay Whale Watch. In the 25 years she's been observing orcas and other cetaceans in theBayy, she's become familiar with how orcas interact with the region's other residents.

The Monterey Bay Whale Watch team had been following about 15 killer whales on the day she captured this drone footage. A sudden tower of condensed air from the blowhole of a blue whale caught the team's attention, and then the killer whales appeared.

Despite being significantly larger than the orcas, the blue whale seemed to be startled by the sudden onset of the pod of predators.

"[Blue whales] are scaredy-cats," says Black.

Perhaps with good reason: While orcas don't typically manage to take down adult blue and grey whales, they will chase whale mothers to separate them from their calves, ultimately wearing out a young whale until it becomes easy prey.

Between April and May, grey whales begin to migrate from their calving waters in Mexico to the feeding waters near Alaska. As they pass by Monterey with their calves in tow, it's common to see an increased number of orcas. Black estimates as many as 33 orcas were in the Bay in April to prey on whale calves.

In the same region in 2012, a pod of humpback whales was observed preventing orcas from feeding on the grey whale calf they had just killed. While the motives of the humpbacks cannot be stated with absolute certainty, similar incidents observed in regions around the world have led scientists to believe the whales may be acting altruistically and protecting other whales from orca attacks.

When hunting large prey like whales, orcas will circle their target, making it more difficult for the animal to escape. Orcas use a variety of methods to communicate underwater, including a complex system of audio calls. Able to hear for tens of miles, orcas signal each other with distinct calls and whistles, and they use clicking sounds to locate prey.

However, orcas are completely silent during a hunt, making it unclear how the animals coordinate their attacks. The recent drone footage shows the orcas emerging stealthily from the water at the same moment in a perfectly formed line.

"They're extremely synchronised. It's incredible," says Black. "We don't know how they're able to be so exact."

According to Black, the attack on the blue whale may have been a sort of practice run, but she thinks it's more likely the orcas were simply roughhousing with the gentle giant.

"They're like kids sometimes," says Black. "They're just going for a reaction."

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