Some female hummingbirds that look like males face less social harassment, study finds

White-necked jacobin hummingbirds may engage in physical fights with other hummingbirds for food.

(CNN)Some female birds are dressed to the nines -- yet oddly interact less with others.

Brightly colored feathers may be the key for these female hummingbirds to avoid physical fights with others of their species.
Female hummingbirds tend to have muted feathers, but researchers found that about 20% of female White-necked Jacobins have bright feathers -- like their male counterparts -- which saves them from being socially harassed, according to a study published Thursday in Current Biology.
    Young birds often start out with female feather coloring, but in the case of this hummingbird species, they are born looking like males, said study author Jay Falk, who worked as a doctoral student in the Cornell Lab of Ornithology and at the Smithsonian Tropical Research Institute during this study. He's currently a postdoctoral fellow at the University of Washington in Seattle.
      Seeing all the juvenile birds look like males, "is pretty unusual in birds, and it was so unexpected that it actually took me a few years to see it in the data," Falk said.
        As the hummingbirds he studied grew up, only 80% of the females molted into drabber colors, leaving the remaining females with male coloring.
        Researchers placed taxidermy mounts of the hummingbirds throughout Gamboa, Panama, and observed how the other hummingbirds interacted with them.
          The females with male coloration faced less social harassment from other male and female hummingbirds compared to their more muted counterparts, Falk said.
          The hummingbirds would often chase or peck one another, he noted.
          Scientists don't know for sure how or why some females keep their male plumage, but the adaptation may be linked to food, said Kimberly Rosvall, associate professor of biology at Indiana University in Bloomington, who was not involved in the study.
          "The data suggests that these more aggressive females with the male-like plumage are better at defending a key food resource," she said. "They do more chasing and are chased less."
          Food that's readily available is a critical resource for hummingbirds because they have a high metabolism, which means they need to eat a lot, said James Dale, professor of zoology at Massey University in Palmerston North, New Zealand, who was not involved in the study.

          Social protections of colorful plumage

          Females might avoid fighting with the brightly colored birds because they could be dangerous, Falk said.
          "She might recognize that drab females are less dangerous, leading her to engage in aggression with drab females," he added.
          While it was rare in the experiment, Falk said males may bother females to court them.
          Male hummingbirds do not help raise their offspring, Dale said, and they're able to have more offspring if they can convince more females to mate with them.
          In the experiment, males preferred to mate with the female hummingbirds who had drab, female coloring rather than the male-colored females, Falk said. However, the males also courted and mated with the male-like female mounts, he added.
          In the future, Falk said he is interested in researching why only some of the female hummingbirds look like males as adults.
            The research has shown how beneficial it is for the female hummingbirds to have male-colored feathers, Dale said, yet most females don't keep their male-colored plumage.
            "Despite the costs of harassment, there must be some benefits to the females that molt into typical female-like coloration," Dale added.