Unlike any other bird, hummingbirds have fascinated experts and everyday nature-lovers alike for generations. However, these fairy-like, nectar-loving blurs of vibrant color have a blood-thirsty side to their existence that very few people see.

Researchers at the University of Connecticut (UConn) have closely observed male hummingbirds during mating season, when they flit through the sky literally fencing one another with their dagger-like beaks for the right to court a female.

And while this may sound romantic at first, it's actually a startlingly violent behavior, during which a little friendly competition degrades into bloody jabs at the throat.

Experts are now arguing that this behavior has some big implications for understanding the evolution of highly aggressive avian species.

Lead researcher Alejandro Rico-Guevara explained in a paper recently published in the journal Behavioral Ecology that bird beaks have historically been a prime example of adaptation through natural selection.

Just think of Darwin's famous Galapagos finches, with their beaks radically changing to tackle new sources of food and challenges. It was thought that this was what solely drove the development of a hummingbird's long and thin beaks - perfectly adapted to drain nectar from deep-throated flowers.

"But we show here the first evidence that bills are also being shaped by sexual selection through male-male combat," Rico-Guevara said in a statement. "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." (Scroll to read on...)

[Credit: UConn]

According to the study, the long-billed hermit, a tropical hummingbird native to Costa Rica, still must woo nearby lady-birds with flashy colors and song. However, before he can do this, he has to reserve a stage for his performance. And apparently the only way to do that is through a duel of the beaks.

"Males are constantly fighting to maintain the best territories," explained Rico-Guevara.

The study details how past observations thought the difference in male and female hermit beaks simply had to do with feeding habits. Now, according to Rico-Guevara and his colleagues, we know better.

The researchers found that during the birds' transition to adulthood, males developed elongated beak tips that were sharper than those of females - weapons that would make them ideal blood letters.

"I think people initially think of them as beautiful, delicate creatures," Rico-Guevera added, "but I enjoy revealing their pugnacious attitudes."