Population of female hummingbirds ‘avoiding harassment by looking as flashy as males’

Due to the wonders of sexual selection, in the bird world bright colours are almost exclusively worn by the blokes.

While female birds can benefit from less flashy feathers – for example camouflage when hiding from predators and incubating eggs – the key driver of the males’ more vibrant wardrobe is attracting a mate, danger be damned.

However, new research suggests that among certain species, these differences between male and female birds’ plumage can mark out the females for unwanted attention from aggressive males.

One species has evolved a neat solution. Over a quarter of the female population of white-necked jacobin hummingbirds in Panama have the same brightly coloured ornamentation as the males.

This similar patterning helps them avoid aggressive male behaviour during feeding, such as pecking and “body slamming”, according to scientists from the Cornell Lab of Ornithology, New York, and the Smithsonian Tropical Research Institute.

Likening it to social ills in the human world which disadvantage women, the researchers say: “Much like in human societies, female hummingbirds have taken it into their own hands to avoid harassment.”

Jay Falk, the study’s lead author, a postdoctoral student at the University of Washington, says: “One of the ‘aha!’ moments of this study was when I realised that all of the juvenile females had showy colours.

“For birds that’s really unusual because you usually find that when the males and females are different, the juveniles usually look like the adult females, not the adult males, and that’s true almost across the board for birds. It was unusual to find one where the juveniles looked like the males. So it was clear something was at play.”

Male white-necked jacobin hummingbirds have bright and flashy colours, with iridescent blue heads, bright white tails and white bellies.

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Female jacobins, on the other hand, tend to be drabber in comparison, with muted green, grey, or black plumage that allows them to blend into their environment.

Dr Falk and his team, however, found that around 20 per cent of adult females also seemed to have similar flashy colouration to the males.

As juveniles, all females initially grow plumage with the bright colours, but this 20 per cent of females doesn’t change to the muted colour scheme as they age.

The researchers said they are not yet sure whether this phenomenon is genetic, occurs due to “choice” by the hummingbird, or is due to environmental factors.

However, the researchers found that it is probably the result of the female hummingbirds trying to evade harassment, including detrimental aggression during mating or feeding.

“Hummingbirds are such beloved animals by many people, but there are still mysteries that we haven’t noticed or studied,” says Dr Falk.

“It’s cool that you don’t have to go to an obscure unknown bird to find interesting and revealing results. You can just look at a bird that everyone loves to watch in the first place.”

To learn why some female hummingbirds keep their flashy feathers, the researchers set up a scenario with stuffed hummingbirds on feeders and watched as real hummingbirds interacted with them.

They found that hummingbirds harassed mainly the muted-coloured females, which is in favour of the hypothesis that the brighter colours are caused by social selection.

Furthermore, most females had brighter colours during their juvenile period and not during their reproductive period. This means that the only time they had brighter colours is precisely during the period when they’re not looking for mates.

In combination with other results from the study, the research team says this indicates it is not sexual selection causing the phenomenon.

In future studies, Dr Falk and his team hopes to use the results of the variation between female white-necked jacobins to understand how the variation between males and females in other species may evolve.

The research is published in the journal Current Biology.