While there are many vocal female birds out there, males generally sing more, and their songs are typically used to repel rivals and attract mates. Yet, female song is an ancestral trait. Now, researchers studying a southern hemisphere songbird species where both sexes sing reveal that females singing in nests draw the attention of predators. The findings are published in Biology Letters this week.
Both male and female superb fairy-wrens (Malurus cyaneus) sing solo "chatter songs" throughout the year to defend their territory against intruders. Their chatter songs consist of eight different vocal elements repeated 50 times for approximately three seconds. The different sexes do show different patterns of parental care: The female incubates eggs by herself, but both parents feed the chicks.
To test if there are gender differences in the costs of singing, a trio of researchers led by Sonia Kleindorfer of Flinders University monitored 72 wild superb fairy-wren nests from September to December in 2013 and 2014 at Cleland Wildlife Sanctuary and Newland Head Conservation Park in South Australia. During this time, three nesting phases would take place: a fertile period followed by incubation and chick-rearing. The team also measured egg predation using iPod-broadcasted songs at 45 artificial domed nests baited with a quail egg at Scott Creek Conservation Park.
The team found that both sexes had higher song rates during the fertile period before egg-laying and lower song rates during incubation and chick feeding periods. Females also sang significantly closer to the nest than males, and they sometimes produce chatter songs inside the nest too, Kleindorfer explains to IFLScience. In fact, 50 percent of the females sang while inside the nest. In addition to chatter songs, these females also produce an "incubation call" with just two vocal elements repeated five times for a second.
As a result, the number of female – but not male – songs per hour predicted egg and chick predation at natural nests, the team found. The singing likely revealed the nest location to predators. At the artificial nests, eggs predation was the greatest at nests where high song rates were broadcasted.
So why sing in the nest if it’s so risky? That’s still unknown for now, but the females didn’t initiate it. Based on the team’s observations, the female produced a song if she happened to be inside the nest when the male sang upon his arrival near the nest. It’s possible that the female song has additional functions such as pair-bonding or vocal tutoring. Though the team thinks that selection should favor some capacity for assessing predation threats when attending a nest.
Image in the text: Robyn Butler/Shutterstock
This post has been updated with additional information on January 19.