Those cute little birds drinking red nectar out of your bird feeder have a dark side.

In a new study published in the journal Behavioral Ecology, male long-billed hermit hummingbirds (native to Costa Rica) use their beaks as weapons to stab each other in the throat as part of a mating game.

That’s taking the whole ‘fight for her’ a little too far.

Bird beaks have often been cited as a solid example of natural selection. But, the study also found “first evidence that bills are also being shaped by sexual selection through male-male combat,” according to Alejandro Rico-Guevara, lead researcher on the study. “It is exciting to think of all these forces working on the way animals look, and to think about how they might affect males and females differently.”

Scientists have known about the differing sizes and shapes in beaks for a while. But, previous explanations pointed to feeding habits. Rico-Guevara noticed the adult male hummingbirds used their bills a lot during fights, and wondered if different shaped beaks presented an advantage.

Rico Guevara’s team found that the hummingbird’s beaks become more elongated and sharper as they hit puberty. Not surprisingly, the hummingbirds with longer, shaper bills tend to win the fights and defend the best territories.

The discovery also offers a potential new way to see the evolution in these bills. Rico-Guevara suggests flowers evolved to conform to longer beaks, not the other way around.

Image credit: Chris Jimenez

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