Some female hummingbirds display male coloring to avoid harassment

0
  • Hummingbirds with the brightly colored feathers typical of males are less often harassed by other birds than those with dull feathers the color of females.
  • The coloring of the male in a species of hummingbird gives a social advantage to females displaying this color pattern.
  • This study is the first to show these behaviors in action with living hummingbirds.

Female hummingbirds sometimes resemble the brightly colored males of their species. Researchers have long pondered the reason for this. Now, a study of hummingbirds in Panama suggests that wearing male-like feathers helps some females avoid intense bullying, researchers recently reported in Current biology.

To find out why this surprising pattern appears, the researchers studied the White-necked Jacobin (Florisuga mellivora), a hummingbird native to Central and South America. These birds exhibit strong sexual dimorphism: physical distinctions between each sex, such as size or color.

The different ornaments of the white-necked Jacobins. From right to left: female-like, male-like, juvenile. Illustration by Jillian Ditner

With a vibrant sapphire head, glistening green back, and glowing white belly, the white-necked male Jacobean looks like a jewel-encrusted figurine. The female slightly tinged with green and white looks dull in comparison.

However, discerning a male White-necked Jacobin from a female is not that straightforward, said Jay J. Falk, who led the study at the Cornell University Ornithology Lab in New York City. Why? First of all, all juveniles of the species display a vibrant male coloration, regardless of gender. Second, up to 30 percent of females retain their male feathers into adulthood, said Falk, who is now at the University of Washington in Seattle.

An evolutionary explanation likely explains this rare violation of conventional avian plumage, the researchers believe.

Scientists hypothesized that male ornamental mimicry in some female birds evolved for social reasons rather than for sexual purposes. However, previous teams had only studied this phenomenon by examining specimens in museums. Falk and his colleagues were the first to see it in action in wild hummingbirds.

“The Falk team relies on [pioneering research] who first defined this field, as is often the case in science, ”said evolutionary biologist Bruce Lyon of the University of California at Santa Cruz. “This study took those ideas and ran with them.”

Falk and his team used mist nets to catch the hummingbirds in flight.  Photo of Ummat Somjee.
Falk and his team used mist nets to catch the hummingbirds in flight. Photo of Ummat Somjee.

Researchers have captured, tagged and microchipped more than 400 white-necked Jacobins near Gamboa, Panama. After identifying their gender through genetic testing, the team filmed the behaviors of birds at feeders, where hummingbirds often act aggressively. Scientists have also observed birds interacting with stuffed and mounted White-naped Jacobins perched on the feeders, displaying both male and female color patterns.

The results were clear: White-necked Jacobin females were more fiercely intimidated if they displayed a dull female colouration rather than a bright male colouration. These skirmishes included pecking or shooting feathers, sometimes in the air, and being kicked out. Male and female birds were the aggressors, along with other species of hummingbirds sharing the feeders.

“People like to think of hummingbirds as these adorable, angelic little creatures, but they really aren’t,” Falk told Mongabay. “Much of the mythology of the Central and South American tribes described hummingbirds as warriors. I think it’s a little closer to the truth.

A white-necked Jacobin with the brightly colored feather patterns typical of males.  Photo of Irène Mendez Cruz.
A white-necked Jacobin with the brightly colored feather patterns typical of males. Photo of Irène Mendez Cruz.

When it comes to mating behaviors, male White-necked Jacobins chose to court stuffed mounts with ordinary female feathers rather than females that looked like males. “This doesn’t mean that female-like females never mate,” Falk said. “[But] given the option, males seem to choose dull females.

Some females of other hummingbird species also look like males, Falk explained, but scientists haven’t explored the reasons. The social selection his team found in white-necked Jacobins may help explain the larger phenomenon, he said.

The patterning of males in female hummingbirds may have evolved due to the amount of food these birds must eat, Falk’s team suspects. Hummingbirds have such a high metabolism that they can starve to death within hours. This, combined with fierce competition for food, creates a system in which eating in peace is a valuable trait.

As Lyon noted, “Because [hummingbirds] are so pugnacious and fiery, it makes sense that you have a system where it pays off not to be hassled.

Quote:

Falk, JJ, Webster, MS, Rubenstein, DR Male-type ornamentation in female hummingbirds results from social harassment rather than sexual selection. Current biology 31, 4381-4387 (2021). doi: 10.1016 / j.cub.2021.07.043

Megan Kalomiris is a graduate student in the Science Communication Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.

Share.

Comments are closed.