CHAPEL HILL — Spying on birds with binoculars while tape recording their sounds on a cattle ranch south of Caracas, Venezuela, a young University of North Carolina at Chapel Hill biologist has discovered that certain male songbirds learn calls only from their fathers. Conversely, females of the species — stripe-backed wrens — learn calls exclusively from their mothers.
Jordan Price says the discovery is unique because it shows how sounds birds produce can reflect both sex and kinship. He described the "his and her" vocal instruction as "a striking example of sex-specific learning."
"Male stripe-backed wrens always produced calls acoustically identical to their fathers’," said Price, who did the research for his doctorate. "Female stripe-backed wrens from the same line matched their mothers’ calls exactly."
Calls of males and females in the same family never matched, he said.
"Twice I found two males living more than a kilometer apart that had nearly identical calls. By looking at records from the 1970s, I discovered that they had the same paternal great-grandfather."
In five years of field work, Price recorded and analyzed more than 10,000 wren calls in the snake and bug-infested, muddy savannah. His mentor, renowned UNC-CH ornithologist R. Haven Wiley, named the sounds "WAY" calls two decades ago because they brought to mind a nasally congested human asking "Where are you? Where are you?"
Neither males nor females duplicated calls from the opposite sex’s repertoire or from any bird but their same-sex parent, he said. A report on the findings appears in the March 22 issue of the Proceedings of the Royal Society of London.
Stripe-backed wrens are termed "cooperative breeders" because they live in family social groups on communally defended territories, Price explained. Within each group, the dominant male and female act as the principal breeding pair while up to 12 other birds — usually previous offspring — do not breed, but help construct the nest and feed the young. When dominant birds die, helpers compete to take their place as breeders.
The UNC-CH student, a behavioral ecologist, investigated about 30 groups of wrens. Much already was known about how the birds were related because of extensive banding dating back more than 24 years and DNA "fingerprinting," which showed genealogy.
The stripe-backed wrens’ communication system is unlike that of any other known birds, he said. Surprisingly, it is remarkably similar to that of killer whales, which also have a comparable social system.
"Almost all songbirds that have been studied so far learn their songs from unrelated neighbors," Price said. "This new system of the stripe-backed wrens makes you wonder. Why aren’t the daughters learning from their fathers, and why aren’t sons learning from their mothers? What’s important for them to learn just from the same sex and not the other."
Perhaps the behavior somehow prevents closely related birds from breeding with one another, he said. Since males and females are indistinguishable by sight, the calls may reveal both kinship and sex.
Studying life in the wild can be exhilarating as well as painstaking, Price said.
"Once I was wading through water two feet deep and all of a sudden there was a big splash, and I found myself almost surfing," he said. "I had stepped on the back of a submerged caiman — an animal that’s a lot like an alligator — and scared him. Another time, I looked up from my notes and was shocked to see a cougar watching me."
Little is known about complex communication between animals living in social groups, Price said. Although his findings are unique among birds, future studies of other highly social animals should reveal similar or even more complex cultural transmission patterns.