Male hummingbirds evolved dagger-like bills for combat

Hummingbirds often seem gentle from a distance. A closer look tells a different story. Life in the forest pushes each bird to compete, react fast, and make sharp choices.

Many hummingbird species guard flowers for nectar, but the green hermit takes a different approach. It pours most of its energy into courtship battles in dim forest clearings across Central and South America.

“They gather together at a place in the forest that looks just like a singles bar,” said Alejandro Rico Guevara, an associate professor of biology at the University of Washington.

“They all have perches, and if someone else takes their perch – their place in the singles bar – they go bananas, and they fight.”

These sessions shape the entire species. Each perch becomes a small stage where sound, movement, and force blend into one contest.

How hummingbirds use their bills

A male green hermit claims a perch and stays alert. A stranger enters the space, and the calm shifts. Wings beat faster. One bird lunges. The other answers.

The bill becomes the main tool in this clash. A sharp, straight point meets a rival’s chest or throat. A single mistake can cost a mating chance. A broken bill can hurt feeding later. Every strike carries risk.

Some related species engage in direct throat stabbing during encounters, hinting at a shared pattern across hermits. These repeated confrontations help explain why bill shape varies so strongly between males and females.

Why hummingbirds change bills

Researchers at the University of Washington studied this species using high-resolution digital models of museum specimens. The patterns were clear.

Males carried straighter and sharper bills, while females showed more curve. The curve helps a female reach nectar in flowers that match her bill shape. The straight form suits other needs.

“Adult male green hermits have reinforced bills because they fight so much,” Rico Guevara said.

This observation fits with a broader idea in hummingbird biology. Sexual selection does not only work through bright feathers or display songs. In this case, competition for a mating perch shapes the tool used in fights.

The team also tested whether size alone explained the difference, but it did not. When the researchers scaled the models to equal size, the male shape still performed better in simulated strikes.

Differences inside the bill

To understand the mechanical side, the team used internal scans. These scans revealed differences in bone and keratin structure inside the bill.

The male form passed force with less bending. It handled stress better. It stiffened under load instead of folding. These traits matter during repeated clashes.

A sharper point also needs less force to pierce. That, in turn, puts less pressure on the rest of the bill. Lower bending, lower stress, lower risk.

The male shape also worked well across a wider range of attack angles. That detail suggests fewer adjustments during a fight.

How strikes work

The way a bird strikes changes the stress pattern in the bill. A horizontal attack spreads force along the surface. A strike that follows the line of the bill pushes stress toward the base.

The second option demands more head movement and puts more strain on the bone. In simulations, the horizontal angle produced better performance for males.

This angle also matches simple flight movement. A bird can fly forward and land a strike without twisting its head or body.

The mechanical differences may shape behavior. A male that delivers effective horizontal hits may keep a perch longer.

That extra control may earn more chances with females. Over generations, this loop pushes bill shape toward sharper, straighter forms.

Hummingbird bills for feeding and combat

“It’s a really cool example of sexually dimorphic weapons in birds,” said study co-author Lucas Mansfield. Most people imagine horns or antlers when thinking about animal weapons.

Hummingbirds rarely come to mind. Yet the green hermit shows that a weapon can form quietly, without extra weight or drag. Small adjustments in length, angle, and thickness create a tool that works in both feeding and fighting.

This research highlights a rare case in birds. Flight usually limits extreme structures, but the green hermit found a narrow space where feeding and combat demands overlap.

The result is a bill that strikes, pierces, and still reaches nectar. A single structure handles two roles shaped by survival, mating, and forest life.

The study is published in the Journal of Experimental Biology.

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