It’s easy to believe that these graceful, dazzling little birds that dance innocently around flowers wouldn’t hurt a fly. But it turns out that male hummingbirds can be surprisingly belligerent, using their long, sharp beaks as weapons to jab rivals in the throat while fighting over females. Because males and females have evolved different shaped beaks, and better weapons are more likely to win battles, researchers believe that this could be the first example of bills being molded by both natural and sexual selection.
Long-billed hermits (Phaethornis longirostis) are large hummingbirds found in forests in central Mexico all the way down to Colombia, Venezuela and Ecuador. They’re generally solitary birds, like most hummingbirds, but the males aggregate and sing together in competitive mating displays called leks. These elaborate rituals also involve tail-waggling and fighting over space. The aim of the game is to maintain the best territory so that once a female enters it, the male can continue to court her with displays and songs before hopefully copulating.
While it’s not unusual for birds to be territorial, these battles piqued the interest of researcher Alejandro Rico-Guevara because he observed that the males would use their bills as swords to stab at their rivals. Male weaponry is rare in birds, so he wondered whether different shaped beaks could confer a mating advantage.
Although it was known that male and female long-billed hermits possessed different shaped beaks, it was presumed that this was likely a result of different feeding habits, which probably served to reduce competition between the sexes.
To find out more, Rico-Guevara and colleague Marcelo Araya-Salas examined 5 different leks for 4 years. The study involved looking at the size and shape of the beaks at different ages and how well the beaks punctured rivals.
As described in Behavioral Ecology, they discovered that adult males had longer and sharper beaks than females and juvenile males. Male birds therefore don’t acquire dagger-like tips to their bills until they transition to adulthood. As expected, males with larger, more pointed bill tips were better at puncturing others and thus were more successful in maintaining their territory within the lek. Together, this suggests that the evolution of male bill morphology is not simply the result of feeding on different flowers, but that sexual selection through male-male combat also plays a significant role.
The duo has already spotted male weaponry in other hummingbird species, so they would like to continue their work by looking at these in more detail.
“I think people initially think of them as beautiful, delicate creatures,” says Rico-Guevara, “but I enjoy revealing their pugnacious attitudes.”