White-Necked Jacobin Hummingbird

Both male and female White-necked Jacobins fan their tails during courtship or aggressive interactions. Because this bird also has its wings partially raised it’s likely an aggressive stance. Credit: Photo by Brian Sullivan/Macaulay Library at the Cornell Lab of Ornithology.

New study finds females that who look like males get more food.

New research on the glittering white-necked jacobin hummingbird reveals nearly 20% of the species’ adult females have male-like plumage. Why? To dodge bullies and get better access to food, according to new Cornell research.

The findings were published on August 26, 2021, in the journal Current Biology.

“What’s interesting about the white-necked jacobin is that all the juveniles start out with male-like plumage,” said lead author Jay Falk, Ph.D. ’20, who did the research with the Cornell Lab of Ornithology as a doctoral candidate. “Among most other bird species, juvenile plumage looks more like the female’s, presumably to be less obvious to predators.” His co-authors are Michael S. Webster, Ph.D. ’91, the Robert G. Engel Professor of Ornithology and director of the Lab of Ornithology’s Macaulay Library; and Dustin R. Rubenstein, Ph.D. ’06, of

White-Necked Jacobin Plumage

The left and center images show adult female and adult male plumages, respectively. Right image shows juvenile plumage. Credit: Artwork by Jillian Ditner, Cornell Lab of Ornithology

As the birds mature, all jacobin males retain the fancier plumage – but so do nearly 20% of the females among the population Falk studied in Panama. The remaining 80% of females develop the muted green and white coloration of a typical adult female.

So, what’s the benefit to females of this species when they look like a male? To solve that puzzle, Falk and his assistants put radio frequency ID tags on birds and set up a circuit of 28 feeders wired to read the tags. By tracking the number and length of visits, they homed in the answer.

“Our tests found that the typical, less colorful females were harassed much more than females with male-like plumage,” said Falk, now a postdoctoral fellow at the

Measuring Wing

Measuring hummingbird wing. Credit: Ummat Somjee