We’re back from a birding/fly-fishing trip and will now finally address The Mockingbird Problem. Northern Mockingbirds – and about twenty percent of other passerine songbirds – are mimics. They steal their songs from their environments. Imagine the smartest student in class unnecessarily cheating on tests by going around the room and copying little bits of every other student’s answers.
That makes no sense. Instead of getting an “A” on the test, the student would get an “F” because her answers would be gibberish. Yet mockingbirds – obviously the star students in avian music class – do precisely that. Rather than develop their own unique songs, they just copy bits and pieces of the songs of other species.
Wouldn’t it be easier and less costly to invent their own songs and pass those down to their offspring? Less brain power would be required and learning would be simpler. Besides, the mockingbird isn’t fooling any other birds. They all recognize that the mockingbird isn’t one of them.
Nobody knows. We think we know that they sing for the same reasons as other birds: the males are seeking, stimulating, and keeping mates and they are competing with one another for mates and territories. But no one knows why they evolved singing songs of other birds. The same question can be asked about other mimics such as Common Starlings, Marsh Warblers, Australian Lyrebirds, bowerbirds, scrubbirds, and African Robin-chats.
We’ve learned a lot about Mockingbird song in the last century though. We know, for instance, that both males and females sing, although females sing only in the summer and only when their mate is off their territory. The males sing most in Spring, less in summer, still less in Autumn and hardly at all in winter. Unmated males sing more than mated males and will, in spring, sing all night long. (I’ve camped on the Chihuahuan Desert and listened to one sing all night long. That mockingbird may have been lonely, but he provided me with one of my favorite backpacking memories.) Unmated males sing in all directions, while mated males tend to sing inward toward their own territories.
The males possess two entirely different repertoires, one for the spring and another for autumn. One had 203 songs in his mind. Somewhere between 90 and 150 seems about average. They continue to learn new songs for as long as they live. Older birds have larger repertoires than younger ones. Males with the most varied songs may get the largest territories. They may also mate earlier. And they sing all the time during breeding season, warbling away while copulating, eating, and foraging.
And probably they sing silently while dreaming. We know that Zebra Finches dream in song; no reason to suspect a bird that devotes as much of its cranial capacity to learning and remembering complex songs wouldn’t also dream in song.
They sing more during full moons.
For more on Northern Mockingbird song see:
Derrickson, K. C. and R. Breitwisch. 1992. Northern Mockingbird (Mimus polyglottos), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/007
doi:10.2173/bna.7 (Subscription Required)
Frank Gill, Ornithology (3rd ed.), pp 230-231 and 237.
For a sample song, try this: http://www.birdjam.com/birdsong.php?id=4
The photo of the Northern Mockingbird at the top is by Manjithkaina, used via a Creative Commons license.