A sparkling violetear and a brown violetear display their elaborate neck side-feathers to intimidate each other and dissuade each other from using their weaponized bills, which feature teeth-like serrations and dagger-like tips.
Image: Cristian Irian, Finca ColibrĂ­ Gorriazul, Colombia

With their elongated bills and specially adapted tongues, hummingbirds are built to extract nectar from flowers. As new research shows, however, some hummingbirds from South America have evolved beaks designed to poke, prod, and pinch—at the expense of feeding proficiency.

Hummingbirds are the ultimate sugar junkies, lapping up the sweet syrupy nectar inside of flowers to get a quick energy boost. Unable to thrive off sugar alone, hummingbirds also eat insects, such as fruit flies, to add important minerals and nutrients to their diets. These tiny birds are voracious eaters, snacking at 10-minute intervals throughout the day. Such is the price for a species that flaps its wings 700 times per second and beats it heart 600 times each minute (or 1,200 times when they’re physically exerting themselves).

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With sugar being the fuel that makes the hummingbird lifestyle possible, nature has bestowed them with a beak fit for the task. Of the 300 species of hummingbirds in the world, most feature specialized bills that can easily slip inside a flower and scoop up the precious nectar inside. These beaks tend to be long and flexible, with soft edges, a blunt tip, and a spoon-like shape. These birds also feature highly specialized tongues that turn into a two-pronged fork when in contact with nectar, allowing the birds to better absorb the liquid.

Hummingbird beaks are also used to snatch insects and for self-defense, but their primary purpose is for nectar feeding—or so we thought. New research published today in Integrative Organismal Biology shows that males of some tropical hummingbird species from South America have beaks more suited to fencing, poking, and pinching behaviors. Ornithologist Alejandro Rico-Guevara, the lead author of the study and a professor at UC Berkeley, said these appendages are used by male hummingbirds to fight off other males, which they do to gain access to food resources and females.

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The beak of male Androdon aequatorialis hummingbirds feature backward facing teeth and hooked tips.
Image: Kristiina Hurme, Colombia

“We understand hummingbirds’ lives as being all about drinking efficiently from flowers, but then suddenly we see these weird morphologies [bill shapes]... that don’t make any sense in terms of nectar collection efficiency,” Rico-Guevara said in a statement. “Looking at these bizarre bill tips, you would never expect that they’re from a hummingbird or that they would be useful to squeeze the tongue.”

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Using high-speed cameras, Rico-Guevara’s team documented peculiar behaviors among certain species of tropical hummingbirds in Colombia, Brazil, Peru, and Costa Rica, including the tooth-billed hummingbird (Androdon aequatorialis) and the saw-billed hermit (Ramphodon naevius). These behaviors included belligerent actions, such as jabbing other birds. Analysis of these bills in the lab revealed physical characteristics consistent with fighting, such as stiff bills, hooked tips, and rear-facing teeth-like serrations. These bills, said Rico-Guevara, are good for poking and chomping an opponent, allowing the birds to pluck the odd feather or two from their rivals.

The likely reason for these weaponized bills, said Rico-Guevara, is on account of more abundant competition between hummingbirds in the tropics. In North America, three or four species of hummingbird compete for resources in a single habitat, while in the tropics the number is closer to 15. For the males with weaponized bills, the adaptation is good for fending off rivals, but it comes at the cost of feeding efficiency. But as Rico-Guevara pointed out, it’s a tradeoff that makes sense.

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“We have discovered that these 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,” said Rico-Guevara. “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.”

The difference between male (top) and female (bottom) beaks of the sparkling violetear hummingbird.
Image: A. Rico-Guevara et al., 2019

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With their tough, pokey beaks, the male hummingbirds are able to protect their food sources. They’re also used to duel other males in pursuit of females at hummingbird gathering places known as leks. Rico-Guevara likens leks to a singles bar, where males gather together and sing their hearts out in hopes of attracting a mate.

“The females go to these small spaces in the forest and pick a male to mate with,” he said. “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.”

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Looking ahead to future research, Rico-Guevara would like to measure the degree to which these males have lost their feeding proficiency as a result of their weaponized beaks, and to understand why some hummingbirds that engage in violence—both males and females—haven’t developed their own weaponized bills.

[Integrative Organismal Biology]

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