The researchers behind a new study in The Auk: Ornithological Advances have discovered that male Red-backed Fairywrens are able to replenish their red feathers throughout the breeding season through “adventitious molt,” the replacement of feathers outside the regular molt cycle.
Male Red-backed Fairywrens attract mates with their bright red breeding plumage, and both color and timing matter—the earlier they molt from their dull nonbreeding plumage into showy black and red, the more attention they get from the females. However, Samantha Lantz and Jordan Karubian of Tulane University have discovered that instead of facing a trade-off between bright color and long-lasting color, males are able to use adventitious molt to actually intensify their coloration over the course of the breeding season.
Males that molted into red-backed plumage during the nonbreeding season started out with the same intensity of red as those who molted later. However, Lantz and Karubian showed that these early-molting males actually increased in redness as time went on by replacing their original red feathers with even brighter ones, so that during the breeding season they were redder than later-molting males.
Early-molting birds change into their breeding plumage before the onset of the rainy season, and adventitious molting may let them take advantage of increased food availability when the rains arrive. Because adventitious molt is hard to document, requiring recapturing the same birds throughout the year, it may be more common that ornithologists realize.
Lantz and Karubian carried out their study with a color-banded population of Red-backed Fairywrens in Australia’s Northern Territory in 2012–2014, capturing individuals during successive nonbreeding and breeding seasons to track the changes in their plumage. “Thinking about it, it actually makes a lot of sense that the wrens would need to replace their feathers periodically, as life in the Northern Territory can be pretty tough,” says Lantz. “The winter is very hot and dry, with lots of fires, and the summer is the wet season, when it rains almost every day. I’ve been caught in a number of thunderstorms there, and I am thankful to be able to retreat under a roof—it’s hard what to imagine it must be like for the wrens, when some of the raindrops are almost as big as they are!”
“The authors have gathered very intriguing evidence that birds can adjust their plumage color after the primary molting period,” adds Dan Baldassarre of the University of Miami, an expert in sexual signals in fairywrens. “This is a very exciting discovery, because molt is typically thought of as a one-and-done event. These results suggest, rather, that molt may be more flexible, allowing individuals to modify their sexual signals throughout the season.”
Male Red-backed Fairywrens enhance a plumage-based signal via adventitious molt is available at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-185.1.
About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.