Male green hermit hummingbirds use their bills both for feeding and as weapons. The birds live mainly in mountain forests of Central and South America, and males gather at display sites to fight over perches and mates. During fights a male raises his long, needle-thin bill and drives it into an opponent; the same bill is used to probe flowers for nectar.
Researchers at the UW Burke Museum led by Alejandro Rico-Guevara made 3D models from museum specimens using photogrammetry and examined internal structure with CT scans. Analyses showed male bills are 3% straighter and 69% sharper than female bills, and the male bill often has a dagger-like tip. CT scans showed the male bill transmits forces more efficiently.
Simulated stabbing tests on the models found the male bill used 52.4% less energy from deformation and experienced on average 39% less stress. The authors interpret these results as evidence that fighting helped drive sexual dimorphism in bill shape. The study appears in the Journal of Experimental Biology.
Difficult words
- evolve — To change over time to adapt or improve.evolved
- bill — The beak of a bird used to eat or fight.bills
- compete — To try to win against others for something.
- structurally — Related to the way something is built.
- phenomenon — An observable event or fact.
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- What do you think about the role of evolution in animal behavior?
- How do you feel about the competition among animals for mates?
- Can you think of other examples where physical traits help in survival?
Related articles
Chimpanzees split and kill former groupmates in Uganda
A long-term study at Ngogo in Kibale National Park found that one large chimpanzee group split into two. Members of the western group later attacked and killed many former groupmates, a result that raises questions about social behaviour.
