Australian Wildfires Rob Fairywrens of Their Flame

(Inside Science) -- Australian wildfires may burn away the testosterone of fairywrens, taking the flamboyant red from the birds’ backs.

Male red-backed fairywrens typically convert their ordinary brown plumage to a striking black and red during the breeding season. Females tend to gravitate toward the brighter males.

In 2012, Jordan Boersma, who at the time was a field technician working at Washington State University, was in northeastern Queensland in Australia determining what conditions cause the fairywrens to molt into their colorful plumage. He and his colleagues had captured many of the birds, marking them with tags and extracting blood samples to test their levels of testosterone -- a hormone that helps trigger colorful feather growth leading up to the breeding season.

Then disaster struck in October 2012, about a month before the fairywrens typically breed. A wildfire burned nearly all the tall grass around the study area researchers had gone to for nearly a decade.

Boersma, now a graduate student at Washington State, helped douse the flames around the donkey paddock where the researchers stayed, but the surrounding area burned. The fairywrens weren’t hurt for the most part -- most took refuge in the donkey paddock. The researchers’ initial experiment was ruined, but a new opportunity to track the effects of the fire arose from the ashes.

In a study published recently in the Journal of Avian Biology, the researchers found that most male fairywrens had much lower testosterone levels after the fire. Very few of the younger adult males molted into their red and black plumage. Older males also molted less frequently, or half-molted in some cases.

“It greatly interfered with these normal patterns of testosterone and ornamentation,” Boersma said. The researchers only observed one pair breeding and nesting in the normal mating period, he added, though it’s possible the season was just delayed way past normal, commencing after the researchers left in January 2013.

Fairywrens have evolved in an ecosystem with frequent burns, so Boersma speculated that the males may be adapted to switch to survival mode when fires come through.

By giving up on reproduction that year, the males can better focus on survival when resources might be scarcer due to the fire, he said, adding that keeping brown plumage may help the males camouflage themselves from predators and avoid fights with each other. He said that just because they don’t change colors doesn’t always mean they won’t breed that season -- some younger males that remain brown still successfully mate.

At the same time, both the prevalence and intensity of fires are projected to increase due to climate change, which could affect fairywren populations over time despite the birds’ flexibility, Boersma said.