Wildfires Change Songbirds' Flashy Plumage

Devastating wildfires can do more than ruin an animal's habitat. They can also challenge their relationships.

In a new study, researchers found that flashy songbirds called red-backed fairywrens didn't molt into their elaborate red and black plumage after wildfires destroyed their habitats in Australia. Their less attractive feathers were also accompanied by a drop in testosterone, which has been linked to the showy plumage. And those flashy feathers are what helps them attract mates.

For the study, researchers measured the birds' level of stress hormone corticosterone and their fat stores, but those remained constant. It was the testosterone that had changed after the fire.

"Really, it ended up all coming down to testosterone," says study lead author Jordan Boersma, a doctoral student at Washington State University. "There's no evidence that the birds were actually stressed. Wildfire was just interfering with their normal, temporal pattern of elevating testosterone and then producing that colorful plumage."

Most male red-backed fairywrens molt, turning from their ordinary brown and white plumage to bright and flashy reddish-orange and black right before breeding season.

"This transition between drab and ornamented plumage is facilitated by increased testosterone, which allows males to sequester the carotenoids in their diet into the bright red colors on their back (less is known about how black plumage is produced, but testosterone is likely involved)," Boersma tells Treehugger.

"While some young males remain drab during the breeding season most acquire the colorful plumage, most likely because females prefer to mate with ornamented males." 

Red-backed fairywrens are accustomed to living through occasional wildfires, so researchers believe that this testosterone change is an evolved response to dealing with environmental changes.

How Testosterone Plays a Role

For the study, which was published in the Journal of Avian Biology, researchers watched the behaviors and took blood samples from fairywrens for five years at two different locations in the northeast part of Queensland state in Australia.

This allowed them to compare birds that experience wildfires with those that didn't.

Shortly after two wildfires in the study, the birds looked for shelter in unburned parts of their habitat, which were mostly horse and donkey paddocks.

"While these areas seemed to be sufficient for foraging purposes, the grass in these unburned paddocks is typically uninhabited during the breeding season as it likely does not support nesting," Boersma says. "This could be due to the grass being insufficient for building sturdy nests or because this short grass is lacking sufficient invertebrate prey for breeding."

Researchers found that after wildfires, diminished ornamentation seemed to be the result of male birds not increasing testosterone production as they typically do prior to a normal breeding season.

"Collectively, it seems that fairywrens might buffer from detrimental effects to personal condition and survival by keeping testosterone low and remaining in drab coloration when breeding is inhibited or delayed," Boersma says.

"Remaining drab likely means that few males were preparing for a breeding season, though it's possible that they could find a mate in their less colorful state. However, it means they would be less desirable to extra-pair mating partners, which is a major component of fitness in this species."

The study findings are specific to this tropical songbird, but they could apply to other species that develop special coloration or ornamentation prior to breeding season.

“It could be a good way to gauge how healthy a population is if you know their normal level of ornamentation,” Boersma says. “If you see that there are very few males undergoing that transition, then there is probably something in their environment that’s not ideal.”