Hummingbirds are tiny, dainty, and, it turns out, rather deadly. Those long, slender beaks they use to sip nectar from flowers double as daggers they need to snuff out opponents, according to a new study published in Behavioral Ecology.

For most of us, discussions of bird beaks are a call back to high school classes on evolution; Darwin’s observations of finches in the Galapagos Islands are the classic example of natural selection by external factors. The beaks of finches can differ depending on what island they live on, a difference based on the type of food that’s readily available. If the easiest food source demands a long, pincer-like beak, birds with those beaks will be able to eat and survive to pass that trait on to their descendants. Birds without that beak shape will die, taking their ill-suited beak shape with them.

In the case of hummingbirds, it seems like a another external factor besides food might have shaped these birds’ beaks.

A male Long-billed hermit’s beak is for nectar…and neckstabbing.

The Long-billed Hermit, a tropical hummingbird native to Costa Rica, has a mating ritual involving leks: a large group of males birds fighting to defend their chosen mating space. Alejandro Rico-Guevara, a research associate in the Department of Ecology and Evolutionary Biology, wondered if the birds in these leks weren’t using their long, pointy beaks as weapons. So he measured the size and “puncture capability” of beak tips in both juvenile and adult hummingbirds.

It turns out that when hummingbirds hit puberty, the males’ beaks become longer and sharper than the females’. It also turns out that they used these long, sharp beaks to stab other males in the throat in an attempt to secure their mating spot.

A male attempting a throat gouge. Can you shout “En garde!” with tongues like that?

It’s the first strong evidence for sexual selection in hummingbirds; more than the need to suck nectar from flowers, the need to defend their space has shaped these birds’ beaks. It’s also extremely strong evidence that these delicate little birds are just as aggressive as the larger predators that we tend to think of as battling each other to the death.

Rico-Guevara, for one, welcomes hummingbirds’ propensity for throat-stabbing. “I think people initially think of them as beautiful, delicate creatures… but I enjoy revealing their pugnacious attitudes.”

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Feature image via Chris Jimenez/UConn