Male green hermit hummingbirds have dagger-like tips on their beaks that appear suited for stabbing rivals during territorial fights, a feature that may explain why males have straighter beaks than females.
Researchers examined the beaks of green hermits using 3D modeling and computer simulations to test how well they perform in puncturing actions. They found that males’ straighter beaks transmit force more effectively and are less likely to break when simulating a horizontal stab, compared to the curvier beaks of females.
“Our results reveal that P. guy exhibits a male-specific bill-tip dagger, and that males’ straighter bills show greater biomechanical performance during stabbing tests, transmitting forces more efficiently (strain energy) and reducing the risk of breakage (von Mises stress),” the team reports in their study, published in the Journal of Experimental Biology.
Hummingbirds often show differences between males and females in beak shape, with females typically having longer beaks in many species. But in hermits, a group of hummingbirds that includes the green hermit, males tend to have longer and straighter beaks. This has traditionally been linked to feeding habits, where different shapes allow males and females to access varied flowers without competing directly.
However, green hermits gather in groups called leks during breeding season, where males compete aggressively for mating rights. Observations of a related species, the long-billed hermit, show males charging and stabbing at each other’s throats with their beak tips during fights.
Building on that, the researchers hypothesized that the green hermit’s beak differences might also stem from combat needs. They created detailed 3D models from museum specimens and used engineering software to mimic stabbing forces, applying loads at different angles to see how the beaks handle stress and deformation.
Males’ beaks proved sharper at the tip, with a narrower angle that likely aids in piercing. In simulations, when force was applied horizontally—as might happen in a direct charge—the male beak deformed less and distributed stress better, suggesting it’s built for efficiency in fights without buckling.“These findings provide further evidence of bill-tip weaponry and support a role of agonistic interactions in the evolution of bill dimorphism,” the researchers conclude.
When the team adjusted for size differences to focus purely on shape, the advantages held: male beaks used about half the energy to deform under horizontal loads and showed lower stress levels overall. Under loads parallel to the beak tip, performance was similar between sexes, but males didn’t lose much edge across angles, implying their straighter design allows for more flexible attack strategies.This adds to evidence that combat, not just feeding, shapes beak evolution in these birds. In long-billed hermits, sharper-tipped males hold better territories, hinting at a link to mating success. The green hermit’s dagger tips might work similarly, though direct observations of fights are needed to confirm.
Bird weapons are rare, partly because flight demands lightweight bodies, but these subtle beak modifications could be a low-cost way to gain an edge in competition. The study suggests such traits might appear in other birds that fight, making weapons more common than thought.“Our bill-tip sharpness metrics indicate that green hermit males possess dagger-like bill-tips, candidate traits to be considered intrasexually selected weapons,” the team notes.
Citations
Alejandro Rico-Guevara et al. Sharper, straighter, stiffer, stronger: sexually dimorphic bill shape enhances male stabbing performance in the green hermit hummingbird (Phaethornis guy). The Journal of Experimental Biology. Published online November 10, 2025. DOI: 10.1242/jeb.250769
