The hummingbird and the flower. It’s a perfect pair. Just look how the long, slender bill matches the shape of the flower. But as anyone with a popular hummingbird feeder knows, these birds are also furious fighters. The Aztecs knew it. Their god of war was a hummingbird. Warriors were known to wear their feathers into battle. They were so on target. Scientists working in Colombia have found that, for some of these birds, evolution has actually turned their beaks into swords. To study these birds, researchers set up high-speed cameras in the rainforest. They recorded interactions that looked like dueling fencers. The hummingbirds had some pretty good moves. There’s the stab, where the bird charges its rival like a jousting knight, or the feint and parry, where the birds fight it out, beak-to-beak, until one tosses the other aside. And, of course, the pinch and pluck, where the birds use their strong bills to bite and rip out feathers. All hummingbirds fight. But in these birds, the males had beaks that had been radically reshaped. These were thicker, more rigid, often hooked at the end. And in some cases, they had jagged points like rows of teeth. These weaponized bills were much less efficient at feeding. The hooked bill and the serrations both interfered with the tongue. But then again, a weaponized bill allowed the males to control access to the flowers. It doesn’t matter how well you drink, if you don’t let anyone else near the nectar. At one time, it seemed like bill shape was all about matching the flower. Now, it’s pretty clear — a bird does not live by nectar alone.