It's that time of year again in the desert (or wherever you are, frankly). The palo verde trees are covered in yellow blossoms. Streetside saguaro cacti sport fat white blossoms. The temperature slowly, steadily climbs toward the triple digit mark. And throughout the urban desert, mockingbirds start to defend their nests again, harassing just about every living thing that comes near.
The northern mockingbird's absolutely fearless defense of its nest probably puts it in the running for bravest animal in the desert. It certainly makes it a contender for most annoying, at least to some people. Mockingbirds are one of those wild animals that do much better in cities than they do in the wild; they have a notable tendency to build their nests near houses. Many are the residents of such houses who venture out on a morning in April or May to find themselves being strafed by a tiny, two-ounce bit of feathers and beak.
You have to give mockers points for guts. When's the last time you took on an opponent who outweighed you by a factor of 1,500? Not that mockingbirds spend most of their energy on harassing human beings. They mostly seem to know that we don't mean them any harm -- in fact, one 2009 study showed that mockers could recognize a human who had previously disturbed their nest, preferentially attacking him while leaving other humans alone.
You will note that while the poor sap in the above video who's been declared Public Enemy Number One by the mockers gets harassed mercilessly, while the person operating the camera is apparently allowed to stand there unmolested. Attacking any humans at all is mildly unusual, though. The threats mockingbirds usually take on are animals known to eat baby birds: snakes, jays, crows and ravens, and -- as in this video -- hawks.
My old dog used to get dive-bombed by a particular mocker each spring in one spot along our daily walk. Raccoons get harassed, possums, even ducks and geese.
But the single thing mockers seem to hate most is cats.
And they might as well. In the urban settings mockingbirds prefer, cats are the single most dangerous predator of baby birds by a considerable margin. Hawks and other big birds are conspicuous. Snakes face more harassment from the nearby humans than they do from the mockingbirds. But cats are stealthy, popular with humans, and essentially subsidized. There are somewhere between 100 and 150 million free-ranging cats in the US, more than any other predator of comparable size. In urban neighborhoods with lots of outdoor cats, survival of some species of baby birds can run to ten percent, or lower. So it makes sense that mockingbirds would reserve special fury for cats in the vicinity of their nests.
Which doesn't mean they're above taunting them:
Of course, the Northern mockingbird (Mimus polyglottos) is not by any means solely a desert bird. These relatives of thrashers maintain a winter range in Northern Mexico and the Caribbean, throughout the southern United States from the California coast to Virginia, and up the East Coast to southern New England. In summer, mockers expand their territory northward, moving into the Owens Valley and Great Basin territory. Birds farther east may summer as far north as Hudson Bay, though most stay south of the Great Lakes. Studied for well over a century, mockers have been expanding their range northward for quite some time, a process already remarked upon in the 1940s.
Whether in the desert or cypress swamp, on the National Mall or on the terrace at the Getty, mockers have adapted surprisingly well to North American cities and suburbs.
This may be due to our landscaping choices: cities' vegetation tends to be more structurally complex than that of neighboring wildlands, adding to the mockers' potential menu of seeds and berries; our profligate use of water boosts the availability of the insect portion of the birds' diet. Mockers often forage on the ground for fallen seeds and ground insects, though they will hunt from perches as well.
Both male and female mockers take part in aggressive nest defense. Mother and father also share in feeding chores, which don't last long: two weeks or less after hatching, baby mockers are about ready to start venturing from their nests. Add that period to the two weeks generally spent laying and incubating eggs, and that means mockingbird parents are on high alert for around a month each year.
The parents can even solicit help from outsiders. Unrelated adult mockers do often help defend other nests, and a persistent alarm call from a besieged mocker can recruit several other adults to the area to harass the stubborn cat, or whatever.
And then, as spring passes into summer, the babies fledge. The adults' blood pressure declines slightly, though mockers never really become unaggressive. An errant hawk or cat may still get The Treatment. Mated couples may part, or they may start the process over again: a pair can raise two or three broods in a breeding season, and go on monogamously to do the same thing next year.
And throughout that year, mockers will do the other thing they do that attracts the ire of city dwellers, especially at 3:00 am:
Both sexes sing, though it's usually unmated males who are the loudest, and who keep on going after last call. Skilled mimics, a mocker can sing another bird's song well enough to fool an accomplished birder -- though actual birds seldom seem to be taken in. A male mocker can learn as many as 200 distinct songs in its decade-long typical life span, including not just other birds' songs but (as seen in an above video) other animals, and an increasingly omnipresent urban "song" we'd all be better off without, the car alarm:
Some years ago, in my old neighborhood in the Bay Area, a neighbor inadvertently trained a generation of local mockers to imitate his overactive car alarm. He bought a new car without an alarm, but for the next few years you could hear the mockingbirds' imitation persist, slowly gaining improvised passages and becoming modified here and there, other bird's songs being folded into the auto security mix. By the time I moved away several mockingbird generations later, the original car alarm song had been amended with with Stellers' jay squawks, the descending whistles of our local white-tailed kits, and clicks sounding remarkably like a barn owl's.
As far as I can tell, no one has reported a mockingbird learning the Nokia waltz ringtone, but it's almost certainly just a matter of time. A mockingbird's song is an echo of the chorus of sounds that surround it. Whether by singing us awake at 3:40 or divebombing us on our way out of the house too few hours afterward, they remind us that there's a natural world just outside our door. personally, I find that worth putting up with a bit of insomnia.
Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Palm Springs regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.
TrackBack URL: http://www.kcet.org/cgi-bin/mt/mt-tb.cgi/13349