California killer whales' violent hunting techniques like tail slapping and headbutting are revealed by scientists who studied mysterious group of predators for 16 years

The killer whales of Monterey Bay have been found to use violent hunting techniques to take down their prey, new research has revealed. 

A team of scientists has been studying one specific group of the fearsome animals since 2006, finding that these whales will feast on everything from sea lions and seabirds to elephant seals and grey whale calves - and use any method to take down their meal.

Their hunting techniques included headbutting, tail slapping to stun it, and even launching their prey into the air.

Images captured in the wild show the apex predators ganging up to separate a grey whale calf from its mother before killing and eating the baby and another captured one orca tossing a dolphin into the air like a ragdoll.

The findings offer a rare glimpse into the world of this group of killer whales, which mostly hunt mammals in the open water and are not very well understood by scientists. 

A killer whale pursues a California sea lion. Sea lions made up nearly half of this killer whale group's prey between 2006 and 2021.

A male transient killer whale slaps its tail down on the water, in an attempt to stun a young elephant seal.

Scientists found that the whales adjusted their hunting behavior depending on whether they were sweeping the open water or searching undersea canyons for prey.

READ MORE: Living up to their 'killer' name!

Watch the 'astonishing' moment an orca individually kills and consumes a great white shark within just two minutes. 

During the observed interactions of this event, at least two white sharks were killed, as evidenced by the discovery of a second carcass measuring 3.55 meters (11.6 feet) nearby.

In open water, they spread out and moved erratically, possibly to cover more space and make it harder for prey to predict their moves.

But in the canyon, they moved stealthily, and scientists suspect they listen to the movement of water to forage for prey in this environment. 

In recent years, killer whales have gained outsized international attention for their coordinated attacks on other predators like sharks, and executing similar attacks against boats.

Last March, for example, a terrified British couple watched helplessly as a pod of killer whales rammed their sailboat over and over, breaking the rudder.

They hunt solo, too, as observed last month when a single killer whale killed a great white shark and removed its liver - their favorite part of the shark - in under two minutes.

In the new study, scientists found that killer whales in Monterey Bay eat sea lions more often than they eat any other prey, with the animals making up about 48 percent of their kills.

One of the observations captured a killer whale stunning an elephant seals with a massive tail slap.

Grey whale calves were the next most common prey, making up about 22 percent of Monterey Bay killer whale kills.

Third most common was the formidable elephant seal, which can weigh up to 9,000 pounds. This large mammal made up about 7 percent of their kills.

A killer whale tosses a Pacific white-sided dolphin into the air. The whales would often hunt these dolphins by coming from underneath and flipping them out of the water.

A killer whale uses its teeth to grip the rostrum or upper jaw of an adult minke whale. The killer whales would often hold larger prey immobile while others attacked.

Harbor seals and common dolphins were next on the list, about six percent each. Least often preyed upon were the occasional seabird, harbor porpoise, Pacific white-sided dolphin, and Dall's porpoise.

Besides what the whales hunted, the researchers also looked for where they hunted. 

They observed that Monterey Bay's deep underwater canyon system seemed to provide a lively hunting ground for the ocean predators.

Deep waters and rocky seafloors make this canyon region ideal habitat for krill, squid, and fish - the foods that their prey like to eat.

Knowing that these tasty lower organisms will bring out the Monterey Bay sea lions, seals, and other marine mammals, this pod of killer whales seems to have learned their meals like to find their meals.

Researchers documented what happens when killer whales gang up to hunt a grey whale calf.

After the killer whales separated the calf from its mother, an adult male rammed it with its head to stun the calf.

There are three main types of killer whales: transients, residents, and offshores.

Residents tend to live in one spot and hunt as a group for small to medium-sized fish like salmon that do not fight back. Their larger family groups make them better at locating their food sources and feeding.

Offshores tend to live in large groups nine miles or more from land and hunt for sharks.

Transients live in smaller groups and hunt mostly mammals - making every excursion a potential fight to the death. 

After stunning the grey whale calf, the killer whales submerged the calf and drowned it by holding it down with their own bodies.

After killing the calf, the killer whales fed on the calf's lower jaw and tongue, its intestines visible above the water and its tail visible below the water's surface at the bottom of the photo

Researchers observed how mammal-hunting killer whales (orcas) in Monterey Bay, California spent their time through 270 hours of behavioral observations. The findings provide insights into predator-prey interactions in this submarine canyon and deep-water environment.

Their name is actually inaccurate, because they tend to stick around the same nearshore areas, like the residents. But decades ago scientists thought they were nomadic, and the name has stuck. 

These pods of transients are the ones that scientists observed in the latest study, carefully cataloguing every sighting of them in Monterey Bay, mapping out their locations, and noting exactly what they were doing.

Most of their time (51 percent) was spent searching for prey, splitting that time pretty evenly between the marine canyon and the open waters.

Ten percent of their time was spent pursuing prey, 23 percent was spent feeding, nine percent was spent traveling, six percent socializing, and one percent resting.

This graph shows the average number of killer whales (black solid line) and grey whales (gray dotted line) in the waters of Monterey Bay each month. Killer whale numbers swelled from March to June, when grey whales migrated through Monterey Bay. In the spring, the grey whales migrate from the tropics with their calves on their way back from their tropical birthing grounds to their Arctic feeding grounds.

Cookie cutter marks on a killer whale indicate that it spends significant time out in the open ocean - where the cookie cutter shark lives.

The group of whales covered in the current study were transients, and even though they hunted some in open water, they were mostly spotted in and around the bay. 

But a fourth group of killer whales has also been identified recently: oceanics.

A previously un-studied group of 49 killer whales has been hunting up to 190 miles off the coasts of California and Oregon, hunting prey as large as sperm whales, according to a study published last week.

Scientists could tell these whales spend much of their time in the open ocean because they bear bite marks from cookie cutter sharks - which only live out there.

People had seen these distinctive wounds on killer whales that live in the southern and western reaches of the Pacific, near New Zealand and Antarctica, over a decade ago.

This deceased grey whale calf was found on the beach in 2011. The day before, scientists had seen a group of killer whales attacking it in Monterey Bay. A and C show the animal's missing jaw, and B shows the parallel slashes made by killer whale teeth.

The 'transient' killer whales actually tended to hunt in the same area over the years, especially favoring the waters of the Monterey Canyon, an underwater canyon system that is ideal habitat for the animals eaten by the killer whales' prey.

But seeing them in the killer whales that live near North America was new. 

Each of these whale groups live extremely different lives, and scientists have observed that they don't even speak the same language.

Over time, though, changes to the environment are changing their habits.

Populations of resident killer whales in many areas are collapsing as salmon runs become less and less numerous.

In some cases, transients are coming in to replace them - thriving on the seals and other creatures that live on the squid and smaller fish that can tough it out where the salmon can't.

Over time, we will see how the transient killer whales adapt to a changing world, too. 

The study was published today in the journal PLOS One.