Early on a crisp november morning biologist Lauryn Benedict strolls through the UC Berkeley Botanical Garden. Suddenly she stops, turns her ear uphill, and points vaguely to a tall pine.
“There’s one. Hear that? A sort of ‘tink, tink.’ There it is again. That’s a call,” she says.
Benedict is on the hunt for a brown, innocuous, pigeon-sized bird that is common to backyards all over the state, the California towhee. Benedict says that while they may not look like much, they do
something that is as mysterious as it is unusual.
Most birds have two types of vocalizations: calls and songs. A call, like the one we’ve just heard, is an often shorter sound that birds use in day-to-day dealings to orient each other, while songs are longer, often more complicated noises that establish territory and attract mates.
“The song is: ‘I’m sexy, come check me out,'” she says. And in spring, “they’ll sing this song almost constantly. And then once they get a mate, they stop singing.”
That’s when things get interesting for Benedict. Rather than sing a lonely song from their perch, a towhee pair will join together and sing a duet unlike either call or song-something extremely rare in the bird world and even more so in North America. No one knows exactly what the duet is for, and few scientists have even studied it, except in the tropics where bird pairs can be so tightly coordinated that they sound like a single bird.
Benedict says the mystery is why evolution, which notoriously dumps extra baggage, would create such a precise behavior, and why in just three percent of birds. The reason, she thinks, may be good old-fashioned romance. Scientists have known for centuries that most birds are monogamous. Many even return to the same mate every year. However, recent DNA testing has shown that many female birds may not be keeping their end of the bargain-a fraction of the eggs in many nests are not related to the male half of the pair.
Towhees, Benedict says, mate for life, do not migrate, and keep the same territory every year. Without the need to establish new territories and find new mates every year, she suspects towhees are much more loyal to each other than are other birds. Therefore, they have time to establish coordinated duets that tell other birds not to enter their territory and discourage opportunities to cuckold the male. If her research bears out her suspicions, Benedict says one might compare towhees and other dueting birds to married human couples.
“You are communicating constantly with an individual that you are spending your whole life with,” she says. “Maybe it’s a love song that they sing to each other.”