Kids learn a lot of things from their dads: how to play catch, how to shave, how to drive. In many cases, it’s obvious that sons have even learned how to talk from their father. Though their voices may be different, the words they use or their pronunciation or mannerisms can be very similar from father to son, almost as if they have been passed down. In some birds, the same familial phenomenon has been observed in the songs of parents and their offspring. But a bird’s song is often hypothesized to advertise their biological fitness to potential mates, which would suggest that at least a portion of that song must be innate and genetically encoded, rather than learned.
Fortunately, one bird species offers a natural experiment to untangle this question of nature vs. paternal nurture: the sordid society of the splendid fairy-wren. When we last visited these Australian birds, male fairy-wrens were using the “scary movie effect” to catch the attention of potential mates, singing their song immediately after the song of the birds’ predator in what researchers Emma Greig and Stephen Pruett-Jones dubbed “vocal hitch-hiking.” That trick is set amidst a social structure that is the stuff of soap operas, where fairy-wrens pair off to raise children, but extra-pair mating is rampant. Roughly 50 percent of offspring result from these extra-pair affairs, meaning that half of the offspring a male fairy-wren helps raise with his female companion is actually from another father.
Unlike migratory birds, male splendid fairy-wrens also stay close to home, assisting their fathers and brothers in defending their territory. So in a paper published by Proceedings of the Royal Society B, Greig, Pruett-Jones, and co-author Benjamin Taft thought they would be a good natural model to test whether song learning is innate, or learned from dear old dad.
“Nobody has ever tested song learning in this situation, where you can factor out the social influence from genetic influence,” said Pruett-Jones, associate professor of ecology and evolution at the University of Chicago.
The researchers split father-son pairs into three groups: fathers raising their biological offspring, fathers raising another bird’s son (“foster” fathers), and fathers who don’t raise their offspring (“cuckolding” fathers). In the first case, the father-son relationship is both social and genetic, but foster fathers have only a social relationship with their sons, while the cuckolding father’s relationship to their sons is purely genetic. Greig then recorded the songs of these fathers and sons, and Taft developed a computer program to statistically correct for individual variations in the grammar of each bird’s song. The songs could then be compared between fathers and sons to detect whether genetics or social parenting was the stronger influence on a son’s song.
In the end, parenting won out. Songs were most similar between father-son pairs who had a social connection, be they dads raising their biological offspring or foster dads unknowingly raising another bird’s son. The songs of sons who were not raised by their biological fathers showed no relatedness to those deadbeat dads, after the statistical correction for song variation.
That result was something of a surprise, as it indicated that the song of male fairy-wrens had little or nothing to do with genetic fitness. If the song of a virile father was passed on to his genetic and “foster” offspring alike, it would carry little information about the sons’ genetics, as only half of them would carry their father’s genes. But that doesn’t mean that the song is entirely meaningless, Greig said.
“The results suggest that social association is more important than signaling quality,” said Greig, now a post-doctoral researcher at Cornell University. “That makes a ton of sense in birds that have long lasting social associations between males in territories. If you have two birds defending one territory, it’s very parsimonious for them to sing the same song.”
An alternate hypothesis was offered by Pruett-Jones, who pointed out that these socially-learned songs will carry information about where the male fairy-wren grew up. Subsequently, when female fairy-wrens seek a mate, they may choose to avoid males with songs too similar to their own, so as not to unintentionally mate with a close relative.
As for those females, Pruett-Jones next hopes to look at the song learning of splendid fairy-wren daughters. Unusually for birds, fairy-wren females also sing songs, making them an interesting subject of research. But the logistical challenges for studying daughters are more difficult than studying sons, because females disperse after their first year of life to find new territories.
“We’re really excited to study females, even though they are harder to study,” Pruett-Jones said. “It may be that they adjust their song to their new neighborhood or adjust their song to their social mate once settled, but maybe there’s still some lingering aspect of songs they heard when they were living with their social dad and social brothers.”
It’s difficult to transfer these results in an Australian bird to how language is learned in humans, but Pruett-Jones said that some basic principles may apply in both species. An individual’s mannerisms of speech or accent usually carry information about where they grew up (at least before air travel became more common), and are hard to change even when they move to another country or learn another language. Whether they learn those speech patterns from dad or mom is yet to be determined.
“There isn’t a genetic signature on language in humans, but our brain is formed once we learn a language, and crystallized by early exposure to sounds and words,” Pruett-Jones said.