On an Argentinian lake in November of 1981, Gary Nuechterlein witnessed a rather disturbing avian assault. A male steamer duck bit and held tight to the neck of another duck called a shoveler, while pummeling the victim with the keratinized knobs on its wings. Meanwhile, “several meters away,” Nuechterlein later wrote in a paper, “a female steamer duck displayed excitedly, calling and stretching” her neck to the sky, as if egging him on.

From time to time the steamer would drag the shoveler under, then resurface and continue beating the tar out of it as the female watched. At one point he shuffled over to her, but after 30 seconds returned to his victim and punched the poor critter 15 to 20 more times. “He then released the limp body of the shoveler,” wrote Nuechterlein, “pecked at it, and released it again.” At last he returned to the female for good, calling to her while she stretched, and the two flew off together. The shoveler eventually regained consciousness, and though seriously crippled, struggled to shore. It died 15 minutes later.

This is the avian version of Bloodsport, only without all of the terrible yet somehow endearing acting. The four species of steamer duck (so named for their penchant for flapping and running along the surface, kicking up water like steamboats) in South America are famous—at least in ornithological circles—for their brutality, getting all up in the grills of not just other steamers, but also other species in scrums lasting as long as 20 minutes. Why exactly they’ve evolved to be so aggressive, no one is yet sure.

Studying these pugnacious creatures is biologist Kevin McCracken of the University of Miami, who learned firsthand that you should watch your step around steamer ducks. “I was down in the Strait of Magellan and Tierra del Fuego and I saw some birds really close to some rocks,” he said. “And I went up to photograph and they were really upset with me, like, amazingly upset with me. And they just came right at me, and started squawking at me.”

Now, had the ducks been guarding a nest, that’d be one thing, but McCracken couldn’t find one nearby. Indeed, Nuechterlein noted in his paper that there needn’t be eggs around to get the ducks riled up and defensive. They’re simply really, really ornery. And that may be because they can take the abuse—by being built like feathered tanks.

You see, their heads and necks are relatively massive for a duck, and they’re equipped with thickened skin to handle the abuse. Because they’re so hardy, they reduce the risk of injury that would normally keep birds from engaging in such vicious battle. (As a rule, in the animal kingdom you don’t want to fight if you don’t absolutely have to. Battling for the right to mate or eat is of course important, but it’s really no use if you end up dead. It’s why there’s all kinds of non-contact battling going on out there, with fancy displays or calls, or even the puffed chest and unimaginative obscenities of the North American dude bro.)

“They’re enormous birds,” said McCracken, adding that males can reach 10 pounds (the famous mallard you’ve no doubt seen around your local lake tops out at 3 pounds). “You don’t want one of these things going after you.”

And woe to any of the steamer’s avian neighbors that aren’t gifted with its bulk, because it could be that steamers are so persistently violent not only to chase other species away to reduce competition for their resources, but to make an example of someone. I’ll reiterate: These ducks have evolved mafia tactics. Says Nuechterlein in the paper describing the fight between the steamer and the shoveler: “Possibly observational learning is important, and holding a ‘public beating’ enhances the effectiveness of territorial displays.” And that, my friends, may be the only time “public beating” has ever appeared in a scientific paper.

Accordingly, bird species unfortunate enough to share a habitat with the steamer duck seem to know their place. When Nuechterlein was making his observations back in the ’80s, he and his colleague noticed silvery grebes and hooded grebes would suddenly skitter or dive en masse. “We puzzled over the cause of these ‘mass spooks’ in the otherwise unmolested flocks of grebes, for there were few predators and no source of human disturbance on the lake.” Only later did they notice the problem: a pair of steamer ducks approaching in a “submerged sneak” posture, with only the tops of their heads and the tips of their tails poking above the surface. They had become, in essence, the Jaws of the Andean lake.

The aforementioned public beating of the shoveler also could suggest aggressive behavior is part of winning the affection of a mate. The female did, after all, grow quite excited as the male pummeled his victim. If true, it would add yet another strange dimension to the exceedingly weird world of duck sex. It’s been well reported, so we don’t need to go into much detail here, but male ducks are notoriously forceful with their choice of mates, and in response females have evolved corkscrew vaginas that in some species twist the opposite direction of the corkscrew penis, all to give themselves more control over the reproductive process. Choosing a male based on how well he assaults another duck, though, would seem to select for such unwanted aggressiveness.

Winging It

The steamer ducks’ brazenness is all the more impressive when you consider three of the four species have grown so big they’ve lost the ability to fly. This would seem unfortunate and rather embarrassing, but we humans tend to romanticize flight. In the natural world, if you don’t use it, you lose it. There’s no point expending energy and resources developing something you aren’t going to use, much less burning vast amounts of energy to fly.

So the flightless species of steamer duck have apparently found it evolutionarily advantageous to stick to terra firma. This is partly due to the relative lack of mammalian predators to flee from (though recently the release of invasive minks, which are fond of bird eggs, has been threatening certain populations). “But they’re also hard to get at,” said McCracken. “If you’re an Andean fox,” which weighs just barely more than these birds, “going after a [10-pound] steamer duck, you’re not going to have much luck.”

And unlike migrating birds, steamers don’t have to worry about wandering in search of food. All species of steamers make their home along the coasts of southern Argentina and Chile, where they use their powerful bills to pry open mussels for a year-round supply of energy—though the unimaginatively named “flying steamer duck” will venture to inland lakes, where it sieves the water for small invertebrates like snails. “So flying is only really necessary if you’ve got to migrate,” said McCracken. “And you’ve got all this food to eat and you live in the ocean, so it’s easy to evolve flightlessness.”

Fascinatingly, we seem to have caught the Falkland steamer duck in this kind of evolutionary transition. What were once thought to be two separate species, one flying and the other that’s grown too darn fat to fly, could in fact be two populations of a single species. And that’s very strange indeed—not to mention a nice little boon for evolutionary biologists. “Partially flighted species remain an exceptional rarity in birds,” write the scientists who made the discovery using DNA testing, “making the South American steamer ducks an ideal resource for future evolutionary research.”

So if scientists can survive observing these things in the wild, they could well bring back some exciting insights into evolution. And probably a few head injuries, too.

A big thanks to Alex Kleine of Hamden, CT for suggesting this week’s creature. Browse the full Absurd Creature of the Week archive here. Have an animal you want me to write about? Email matthew_simon@wired.com or ping me on Twitter at @mrMattSimon.

References:

Nuechterlein, G. and Storer, R. (1985) Aggressive Behavior and Interspecific Killing by Flying Steamer-Ducks in Argentina. The Condor. Vol. 87, No. 1, pp. 87-91

Fulton, T.L., Letts, B. and Shapiro, B. (2012) Multiple losses of flight and recent speciation in steamer ducks. Proceedings of the Royal Society. 279, 2339–2346 doi:10.1098/rspb.2011.2599