Blue whales might be rather clever foragers. (AP Photo/Cascadia Research, John Calambokidis, File)

With tongues as heavy as elephants, blue whales are the largest known animal ever to roam the Earth. But the 100-foot-long, 200-ton creatures live on shrimp just 2 inches long. It takes 4 tons of krill per day to feed the average blue whale, so you might assume that the giants just have to vacuum up every tiny shrimp they come across. According to a new study, however, the blue whale is actually a very discerning forager.

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In a study published Friday in Science Advances, researchers report that blue whales are experts at finding the densest patches of krill in the sea.

When blue whales feed, they suck up literal tons of water — sometimes as much as their own body weight — and force it back out through their fringed, fingernail-like teeth. Tiny krill are left behind to make up the meal.

By observing tagged whales and tracking their behavior, researchers found that the whales are less likely to make a big gulp when they're in areas with low numbers of krill. It's a high-energy process, and it turns out that the whales are too smart to waste their time. In areas dense with krill, they'd ramp up their feeding to make up for the loss.

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"Blue whales don't live in a world of excess and the decisions these animals make are critical to their survival," co-author Ari Friedlaender, a principal investigator with the Marine Mammal Institute at Oregon State University's Hatfield Marine Science Center, said in a statement. "If you stick your hand into a full bag of pretzels, you're likely to grab more than if you put your hand into a bag that only had a few pretzels."

The study helps explain previous research, which had shown that blue whales yield massive energy returns on their feeding. One study found that blue whales yield 90 times the energy they use when they feed, which is incredible when you think of the 750,000 or so calories a whale burns during each dive.

The researchers hope that their work will help in efforts to protect the species, which is endangered.

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