A female white-necked jacobin hummingbird with male-like plumage. Credit: Irene Mendez Cruz/UW
While deception generally carries a negative connotation, female hummingbirds have found a way to leverage trickery to their benefit.
According to a new study, about 20% of female white-necked jacobin hummingbirds intentionally make themselves look like males in order to stave off aggression from their notoriously bullying counterparts.
As juveniles, white-necked jacobin hummingbirds sport colorful blue-and-white plumage. When they grow into adulthood, however, only males retain this pattern. Conversely, females develop a more “muted” palette of green and white—at least, most females.
Interestingly, 1 in 5 adult females defy the norm and retain blue-and-white male plumage into adulthood. New research by Jay Falk, a postdoctoral researcher at the University of Washington, shows this is intentional—the females are actively engaging in “deceptive mimicry.”
Researchers have recorded many examples of deceptive mimicry between species in the past. For example, some non-venomous kingsnake species have evolved colorful banding patterns that resemble venomous species that live in the same area, such as coral snakes. Research has shown that this deceptive mimicry decreased predation of the kingsnakes, which are not venomous.
The strategy appears to have also worked for the female white-necked jacobin hummingbirds. According to Falk’s study published in the Proceedings of the Royal Society B, females with male-like plumage indeed suffer less aggression from males compared with females that have the more typical muted plumage.
But, despite their look-alike features, these females do not act like males. To test this, Falk briefly captured male jacobins and females with both types of plumage at a field site in Panama. He discovered that females—regardless of plumage—had essentially identical body and wing sizes, whereas males were slightly larger.
Before releasing the birds, Falk also tested their “burst power”—or muscle capacity during flight— y seeing how high they could fly while lifting a chain of small, weighted beads. Females of both types of plumage had identical burst power, while males could lift more on average.
Additionally, using data from radio-tagged birds in the wild, the research team discovered that more males fed in a “territorial” pattern, spending longer amounts of time at a smaller number of feeding sites. Meanwhile, females—again regardless of plumage—showed the opposite pattern: feeding for shorter periods of time at sites across a larger territory.
But, Falk says, differences between the sexes may not be the whole story.
“Even when I found average differences in female and male morphology, burst power or behavior, I also found quite a bit of overlap between the sexes,” he said. “That indicates that sex isn't the only important factor, and that variation among and between individuals plays an important role.”
That leads Falk to the next part of this research—studying the role of individual variation in these traits, regardless of sex. The biologist will also be examining the genetic differences between females with muted and male-like plumage and working to identify how this deception mimicry first evolved.