Watch: Kickboxing Kangaroos and 4 of Nature’s Most Impressive Fighters

The incredible video of two kangaroos kickboxing in suburban Australia that made the rounds last week has become a smash hit, with more than four million views on YouTube.

Rod Langham, of Wyee Point in New South Wales, filmed the evening fight in his neighborhood, where kangaroos are common sights, according to news reports.

“I was just having a coldie after a hard day’s work and was interrupted by a street fight,” he told Australia’s Daily Telegraph newspaper.

The video—and its popularity—got us curious about which other species are known to battle with their own kind. (See “Animal Fight Night” on National Geographic Channel.)

The short answer: Most animals avoid a fight if they can help it—but sometimes push comes to shove.

“This is a costly and even deadly behavior … So animals don’t really fight their own species unless there’s a really good reason or the stakes are really high,” said David Steen, a wildlife ecologist at the Auburn University Museum of Natural History in Alabama.

“It usually relates to reproduction. Males will often fight for reproductive access to a female, and females will often fight to defend their young.”

Steen shared his surprising picks for the top four most impressive fighters in the animal kingdom.

Rattlesnakes

When two eastern diamondback rattlesnake males meet, “they’ll size each other up, and if they’re a similar size, they’ll engage in combat,” said Steen.

“The front third of their body will stand up in the air, and they’ll wrap their necks around each other and try to wrestle each other to the ground—basically pinning each other and pushing each other down.”

For the most part, rattlesnakes tangle (literally) to gain mating rights when there’s a female in the area, and they have little interest in the fight turning fatal for either of them, Steen noted.

“This is really a costly behavior, so some animals have evolved the strategy … of ritualized combat rather than actual tearing of flesh and bone; [that way,] they can go through this without hurting or killing each other,” he said. (See National Geographic’s rattlesnake pictures.)

Indeed, despite possessing a powerful venom, Steen says diamondbacks rarely bite each other when engaging in such ritual combat.

“They don’t do it do the death. I don’t know how they figure out who won, but eventually one decides that he’s been bested and he crawls [away.]”

Lions

Next up is the king of the jungle himself: the African lion. Steen says that when lions fight, it’s usually about social hierarchy and all the benefits that come with being leader of the group.

“Lions are famous for living in [prides], with a dominant male and harem of females and cubs,” says Steen. “Other males will challenge the dominant male for the right to lead the pride.”

“And a smaller male probably wouldn’t try it on his own, but sometimes the solitary males form little prides of their own and will try to usurp a dominant male.” (See “The Serengeti Lion” in National Geographic magazine.)

Lion battles are riskier than the ritualized combat seen in rattlesnakes, for instance.

“When a dominant male is challenged, he’s got a lot of stake in winning that fight because he’s already reproduced, a lot of his cubs are in that pride, and one of the things a new male will do is kill all of those cubs.”

As a result, “those are pretty vicious fights,” says Steen.

Chickens

Yes you read that right. Chickens.

“Think about it,” said Steen. “There’s a whole industry of fighting roosters. What they’re doing is capitalizing on their natural behavior.”

Steen explained that the modern domesticated chicken descends from an Asian bird known as the jungle fowl—and that it’s built for battle.

There are four species of jungle fowl, and all of them “have these little spurs on their feet, which are for the purpose of fighting other males,” says Steen, noting that they probably also use them to fight off predators. (See “Half-Male, Half-Female Chicken Mystery Solved.”)

The brutal practice of cockfighting, in which chickens often fight to the death, is illegal in all U.S. states. In countries where it’s still practiced, cockfighters often enhance the roosters’ natural weaponry by putting little blades on their foot spurs, “and that increases the damage potential,” said Steen.

Even on your run-of-the-mill chicken farm, rooster aggression is well known, Steen said.

“That’s probably why most farms only have one rooster.”

Tortoises

Perhaps almost as surprising as chickens is Steen’s fourth choice: tortoises.

“They have this reputation as being these slow, docile creatures, but they will also fight with each other for the opportunity to mate,” says Steen.

For instance, male gopher tortoises of the southeastern U.S. boast a built-in weapon—a jutting piece of shell called a gular projection—that helps it flip the rival tortoise on its back.

“That’s a pretty precarious position for a tortoise,” says Steen. “So when one is on its back, the fight is over and the victor is free to court the female.”

So does the victorious tortoise finish his rival off while he’s upside down and at his mercy?

“No, but when a tortoise is on its back, it’s really vulnerable to exposure or to predators, so it is sometimes a death sentence,” explains Steen. (Also see “Galápagos Tortoises: Slow and Steady Migrators.”)

Steen stresses that even the best animal fighters try to avoid risky duels.

“They always want to avoid the fight if possible … So they’ll often do displays and puff themselves up to make them look bigger, and if one animal is bigger than the other, [it] will leave the fight,” he said.

“The big fight generally happens when they can’t figure out who would win, and then they go at it.”

For all of us watching on YouTube, may the best animal win.

Follow Stefan Sirucek on Twitter.