Hummingbirds are frenetic little creatures—they can beat their wings between 10 and 80 times per second—and thus require plenty of food to fuel their high-energy lifestyle. The birds’ elongated bills are designed to dip into flowers and lap up their sweet nectar. Scientists often cite the relationship between hummingbirds and plants as a classic example of co-evolution: the birds get a reliable source of food, and in turn act as guaranteed pollinators for flowers. But as George Dvorsky reports for Gizmodo, a new study has found that some hummingbirds have evolved bills better suited to a different purpose: fighting.
Many hummingbirds have flexible bills with soft, concave tips—perfect for scooping nectar out of flowers. These appendages also form a nice seal around hummingbirds’ nifty tongues, which fork when they hit pools of flowers’ sugary goodness. Not all hummingbird bills, however, look this way, as a team of researchers discovered when they studied several species of hummingbirds in the tropics of South America.
As part of a study published in Integrative Organismal Biology, the researchers used high-speed cameras to observe the birds getting up to all sorts of nasty behavior: pinching, pulling on feathers and even fencing with their bills. Upon further examination in the lab, the researchers found that the males of these swashbuckling hummingbirds boasted unique bills that were relatively stiff and straight. Some species even had hooks, daggers and teeth-like serrations lining their bill tips. And that was rather strange, since their unusual bills likely make the hummingbirds less efficient feeders.
“We understand hummingbirds’ lives as being all about drinking efficiently from flowers, but then suddenly we see these weird morphologies—stiff bills, hooks and serrations like teeth—that don’t make any sense in terms of nectar collection efficiency,” says Alejandro Rico-Guevara, an evolutionary biologist at UC Berkeley and the lead author of the study.
These adaptations do, however, make sense when it comes to poking other birds, or even yanking out a few feathers. Some male tropical hummingbirds have evolved to be fierce fighters; male wings, for instance, are more aerodynamic, making them better suited for in-flight duels, the researchers found.
Tropical hummingbirds are certainly not the only members of the Trochilidae family that are known to get aggressive. Plants do not constantly secrete nectar, so the birds have to defend their favorite flower patches from competitors itching to swoop in and gobble up precious meals. But that competition is stiffer in South America, where as many as 15 hummingbird species might square off with one another in single habitat. Elsewhere in the Americas, only three or four species are likely to be competing for resources.
“We have discovered that these [weaponized bill] traits may be related to a different kind of strategy: instead of feeding on a particular flower shape very well, some birds try to exclude everybody from a patch of flowers, even though they can’t feed as well on them as hummingbirds without bill weapons,” Rico-Guevara explains. “If you are good enough at keeping your competitors away, then it doesn’t matter how well you use the resources in the flowers you are defending, you have them all to yourself.”
Stiff, sharp bills aren’t only handy for chasing other birds away from tasty nectar; some hummingbirds, according to the study authors, use their handy weapons to ward off competition for females. In the tropics, the males of several hummingbird species gather in special spots—known as “leks”—to strut their stuff by vocalizing for females.
“A lek is like a singles bar,” Rico-Guevara says. “If you can get a seat at that bar, it is going to give you the opportunity to reproduce. So they don’t fight for access to resources, like in the territorial species, but they actually fight for an opportunity to reproduce. And in the brief moments when there is no fighting, they go to feed on different flowers.”
Moving forward, Rico-Guevara hopes to unpack other questions about bill adaptations among tropical hummingbirds—like why females, who also occasionally fight one another—are not armed with the same bills as their male counterparts. But for now, the study adds nuance to our understanding of the forces that have driven hummingbird evolution.
“We are making connections between how feisty they are [and] the beak morphology behind that,” Rico-Guevara says, “and what that implies for their competitiveness.”