Female birds in the families of warblers, manakins, starlings and other songbirds are lovely, but the most of the males are much prettier.
Female Vermilion Flycatchers, Red-winged Blackbirds and Painted Buntings simply aren’t as eye-catching the flamboyant boys. Indeed, these species and many others are named for male colors that the females lack.
By Rex Graham
Of course, there are welcome (to birdwatchers) exceptions to what evolutionary biologists call “dichromatic” discrimination. Equal color rights are found in Red Warblers, Paradise Tanagers, Superb Starlings and Superb Pittas.
However, are these colorful females merely cross-dressing, or do bright colors give them advantages over predator-avoidance camouflage?
Females Favoring Color over Camouflage
“The bright coloration of females in some species was generally just considered a side-effect of the colourful plumage being favoured in males,” James Dale, Associate Professor of Evolutionary Ecology at Massey University in New Zealand, said in an email. “What our research has done is shown clearly that colourful plumage in females is functional and important.”
Really? What are the rules that govern wide and variable differences in male and female plumage colouration?
“The evolutionary causes of this diversity are not well understood,” wrote Dale and his co-authors of a paper in the Nov. 4, 2015, issue of the journal Nature. However, the researchers from New Zealand, Canada, Australia and Germany arrived at three new conclusions about male-female coloration differences in 6,000 species of perching birds:
- Larger birds tend to have not only more coloration, but also similar coloration in males and females. The scientists theorize that larger female birds face less predation than smaller birds, and they gain more from upgrading from earth tones to reds, yellows and glossy blacks than they lose.
- Birds in equatorial regions are more colorful than birds breeding farther north or south, and the coloration differences between the sexes are less. In these areas, non-migratory males and females both compete for mates. The prettiest girls want the prettiest boys, and they want those boys to form a pair bond with them.
- When males compete fiercely with each other to win mating rights to multiple females, they are almost always more colorful than females. When these females rear their young without paternal help, hormones often limit their development of colorful feathers or eye-catching ornaments.
“Our statistical approach analyzed the relative strength of 10 factors, alone and in combination, in determining similarities in male and female plumage colouration,” Dale said. “Although the patterns we report are very strong, it is easy to find many exceptions. By no means have we captured all the predictor variables.”
Female Birds Colorful Advantages
Every birdwatcher has observed males of one species posturing or fighting over food and territory. These pugnacious males may advertise their competitive advantage in the form of ornamentation and more colorful feathers.
Dale and his colleagues suspect that females may gain similar non-sexual advantages with ornaments or colorful feathers. More colorful females may thus win the most food and turf battles.
Dale said the Heuglin’s Robin (White-browed Robin-chat) of Tropical Africa is one of the best examples of a species that fits the profile of one in which both male and female are brightly colored. In this case, male and female robins sing to defend territory as a team. He said there are many similar examples.
“Black turns out to be a strongly male-biased coloration, so crows and ravens are good examples of large ‘colorful’ birds of both sexes,” Dale said. “Many jays are also comparatively large, and both sexes are also more stereotypically colorful. There are many other examples – Pittas, Starlings, Broadbills and several large thrushes.”
The latest research has raised speculation that some colored female birds use their bright plumage as a type of “armament” in non-sexual, socially competitive situations. “Hopefully our study will contribute to stimulating future research on how exactly the females of tropical species use their colourful plumage,” Dale said.
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