What do Arkansas, Florida, Mississippi, Tennessee and Texas have in common — other than a passion for college football? They've all chosen a feathered plagiarist as their official state bird. The Northern mockingbird's scientific name, Mimus polyglottos, means "mimic of many tongues." It can imitate the noises made by cardinals, blue jays, wrens, titmice and a variety of other birds. Even more remarkable is this creature's spot-on impressions of car alarms and squeaking gates.
Mimus polyglottos is just one of the 14-plus mockingbird species out there. Many of these birds are known to replicate the sounds of other animals, which begs the question of "why?" Why do mockingbirds "mock?" What evolutionary advantage does this musical talent offer? And do they ever stop learning new songs?
To get some answers, we talked to biologist Dave Gammon of Elon University in North Carolina. Mockingbirds happen to be his specialty. "I started studying them over a decade ago," he says in an email. "Everyone was interested" in these mimicry specialists back then, "but no one studied their mimicry for longer than a year or two."
His investigations into their behavior cast doubt on an old assumption. Some birds like macaws and the European starling are capable of picking up new songs throughout their lives. They're what's known in the parlance of neurobiology as "open-ended learners." Other birds are "close-ended learners," which is to say they cannot master any new songs after reaching a certain age.
Ornithologists used to think mockingbirds were open-ended learners. That no longer seems to be the case. Gammon once compared many years' worth of recordings from 15 individual mockingbirds. If these feathered musicians were constantly learning new songs, you'd expect their repertoires to get bigger and bigger with age. Instead, Gammon found that the birds did not expand their personal song banks as they got older. "I think it's safe to say," Gammon says, "... that mockingbird song-learning is not as open-ended as most folks originally thought."
The mental roots of avian song acquisition are worth exploring. Eliot Brenowitz is a professor of psychology and biology at the University of Washington. He's an expert on neurological development in birds and is fascinated by the ways our feathered friends learn to vocalize.
For some close-ended learners like zebra finches, hatchlings have just one year to memorize all the songs and calls they'll need to know as adults. Then the window closes and their ability to learn new material disappears. "In bird species that learn songs only as juveniles, a region of the brain necessary for learning (called LMAN) decreases in size and neuron number during the first year of life after hatching," Brenowitz says via email. He adds that other "molecular changes" in the brain conspire to make learning more difficult as time passes. "No one has yet studied the brains of juvenile mockingbirds, so we don't know whether similar changes occur during their first year of life."
Mimicry, Uncertainty and the Scientific Process
Nature is chock full of animals who mimic each other. Harmless milk snakes have evolved to resemble deadly, venomous coral snakes so they can better deter predators. Alligator snapping turtles use wriggling, worm-shaped lures on their tongues to attract hungry fish. So what benefit does one bird derive from copying another bird's calls?
That depends on the species. The African fork-tailed drongo imitates other birds' alarm calls in order to scare its neighbors away and steal their food. Male satin bowerbirds try to woo potential mates by copying the songs of crows, cockatoos, kookaburras and the like. The ones with the most convincing impressions have the best chance of reproducing. "Mimicking the vocalizations of other species may be physiologically or mechanically difficult, and females may choose males on how accurately they [do so]," Brenowitz says.
Scientists aren't sure about why mockingbirds mock, though. Gammon says that robins and cardinals don't change their behavior when northern mockingbirds imitate their calls. Therefore, it seems unlikely that the mockingbirds are trying to manipulate other species through vocal mimicry.
An adult male mockingbird can emit up to 200 distinctive noises. You might be surprised to learn that these birds do have songs of their own, melodies that are not lifted from other avian species. Mockingbirds are most likely to imitate sounds — like titmouse cries, cardinal chirps, and yes, even car alarms — that are acoustically similar to the rhythm and pitch of their own voices. Nobody knows why that is.
"For me, the jury is still out on whether [any existing hypothesis] can explain mimicry in mockingbirds," Gammon says. "In science, it's better to embrace lingering uncertainty than to be proven wrong later on. Hopefully, future data will provide a clear path forward."