Female hummingbirds avoid harassment by looking as flashy as males
IMAGE: THIS IMAGE SHOWS A MALE-LIKE FEMALE WHITE-NECKED JACOBIN HUMMINGBIRD BEING RELEASED AFTER CAPTURE AND TAGGING. view more
CREDIT: IRENE MENDEZ CRUZ
Much like in human society, female hummingbirds have taken it into their own hands to avoid harassment. By watching white-necked Jacobin hummingbirds in Panama, researchers discovered that over a quarter of females have the same brightly colored ornamentation as males, which helps them avoid aggressive male behaviors during feeding, such as pecking and body slamming. This paper appears August 26 in the journal Current Biology.
“One of the ‘aha moments’ of this study was when I realized that all of the juvenile females had showy colors,” says first author Jay Falk (@JJinsing), who is now a postdoc at the University of Washington but led the research as a part of the Cornell Lab of Ornithology and Smithsonian Tropical Research Institute. “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 are known to have bright and flashy colors, with iridescent blue heads, bright white tails, and white bellies. Female Jacobins, on the other hand, tend to be drabber in comparison, with a muted green, gray, or black colors that allow them to blend into their environment. Falk and his team, however, found that around 20% of adult females have showy colors like males.
As juveniles, all females have the showy colors, but this 20% of females doesn’t change to the muted color as they age. It is not clear whether this phenomenon is genetic, by the choice of the hummingbird, or 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 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 kept their showy colors, 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 colored female hummingbirds, which is in favor of the hypothesis that the showy colors are caused by social selection. Furthermore, most females had showy colors during their juvenile period and not during their reproductive period. This means that the only time they had showy colors is precisely during the period when they're not looking for mates. In combination with other results from the study, this indicates that it is not sexual selection causing the phenomenon.
In the future studies, Falk and his team hope 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.
This video shows a white-necked Jacobin of an unknown gender visits a data-logging feeder in Gamboa, Panama installed by the researchers.
The authors received financial support from the Smithsonian Tropical Research Institute, the National Science Foundation, the Cornell Lab of Ornithology, the Cornell Department of Neurobiology and Behavior, the Society for the Study of Evolution, the American Society of Naturalists, and the Sigma Xi Society
Current Biology, Falk et al.: “Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection” https://www.cell.com/current-biology/fulltext/S0960-9822(21)01033-2
Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.
JOURNAL
Current Biology
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection
ARTICLE PUBLICATION DATE
26-Aug-2021
Some hummingbird females look like
males to evade harassment
New study finds females that look like males get more food
IMAGE: THE LEFT AND CENTER IMAGES SHOW ADULT FEMALE AND ADULT MALE PLUMAGES, RESPECTIVELY. RIGHT IMAGE SHOWS JUVENILE PLUMAGE. view more
CREDIT: ARTWORK BY JILLIAN DITNER, CORNELL LAB OF ORNITHOLOGY.
Ithaca, NY—New research on the glittering White-necked Jacobin hummingbird reveals nearly 20% of the species’ adult females have male-like plumage. This strategy is all about dodging bullies and getting better access to food. The findings were published today in the journal Current Biology. [LINK]
"What's interesting about the White-necked Jacobin is that all the juveniles start out with male-like plumage," explains lead author Jay Falk. "Among most other bird species, juvenile plumage looks more like the female's, presumably to be less obvious to predators." Falk did this work while a Ph.D. student with the Cornell Lab of Ornithology and is currently at the University of Washington.
As the birds mature, all the 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 still develop the muted green and white coloration of a typical adult female. Though plumage ornamentation is usually attributed to sexual selection and attracting a mate, researchers ruled out that explanation for this species after field experiments.
Funding for this research was provided by the Cornell Lab of Ornithology, the Smithsonian Tropical Research Institute, the National Science Foundation, the Society for the Study of Evolution, the American Society of Naturalists, and the Sigma Xi Society.
Scientists observed the reactions of live jacobin hummingbirds toward stuffed mounts placed on nectar feeders during breeding season. The mounts were stuffed specimens of adult White-necked Jacobin males, typical adult females, and female adults that looked like males.
"If females having male-like plumage is the result of sexual selection, then the males would have been drawn to the male-plumaged females," says Falk. "That didn’t happen. The male White-necked Jacobins still showed a clear preference for the typically plumed adult females."
So, what's the benefit to females of this species when they look like a male? To get to the root of 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 honed in the answer.
"Our tests found that the typical, less colorful females were harassed much more than females with male-like plumage," Falk says. "Because the male-plumaged females experienced less aggression, they were able to feed more often—a clear advantage."
CAPTION
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.
The researchers found that the male-like females got to feed longer than the typical adult female—about 35% longer at feeders filled with high-sugar nectar. That can make a big difference because hummingbirds have the highest metabolic rate of any vertebrate. They need to eat constantly in order to survive.
Bottom line: female White-necked Jacobins retain the male-like plumage of their youth for social reasons—they avoid the bullies by looking like them. It is still not clear whether male-like females behave just as aggressively as the males. The actual physical mechanism that allows females to retain male-like plumage is also not known.
The White-necked Jacobin is hardly alone when it comes to having some females that look like males. Falk says studies have found that 25% of the world’s 350+ hummingbird species also have some females that look like males.
CAPTION
Field assistant Pedro Luis Castillo-Caballero glues antennas to feeders for radio frequency ID experiment in Gamboa, Panama.
CREDIT
Photo by Jay Falk.
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JOURNAL
Current Biology
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection
ARTICLE PUBLICATION DATE
26-Aug-2021
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