Alejandro Rico-Guevara, UW Biology associate professor and curator of ornithology at the UW Burke Museum, was featured in a UW News article about research on the bill shape of green hermit hummingbirds. Compared to their female counterparts, male green hermits’ bills are straighter, sharper and structurally stronger. The straighter bills work better as weapons, while female birds’ more curved bills provide improved access to nectar in some flowers. The findings suggest that green hermits’ bill sexual dimorphism — when two sexes of a species exhibit different characteristics — was likely driven by their tendency to fight, not solely by ecological factors.
Excerpt from the UW News article:
“Adult male green hermits have reinforced bills because they fight so much,” Rico-Guevara said. “It’s the same tool, but in very different contexts. This is an example of how much we can still learn from sexual dimorphism in nature.”
In the study, published Nov. 10 in the Journal of Experimental Biology, researchers selected green hermit specimens from the Ornithology Collection at the Burke Museum and used photogrammetry to develop 3D models of male and female bills. Through curvature and angle analyses of those models, researchers found that male bills are 3% straighter and 69% sharper, respectively, with a dagger-like tip not found on female bills.
But the differences, researchers found, extend beyond bill shape. CT scans revealed that the male bill’s internal structure provided additional strength by transmitting forces more efficiently.
Finally, researchers ran the models through a series of simulated stabbings to stress-test the bills in both head-on and angled attacks. They observed that the male’s straighter bill expends 52.4% less energy due to deformation, and is more resistant to breaking. The male bill experienced on average 39% less stress than the female bill.
They also found that male bills’ straighter shape can accommodate a wider variety of attack angles, requiring less precision while fighting.
Read the full article in UW News.