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ANIMALS

Why the Mockingbird Sings : And Why at Night, When Most Birds Sleep?

January 25, 1987|WILLIAM JORDAN | William Jordan is Long Beach-based science writer.

I was lying there one morning last October, somewhere between one-third and one-quarter conscious in the softening darkness. The first sounds of dawn were tinkling dimly in the distance as a mockingbird warmed his throat for the day's performance. Then, suddenly, I was bolt upright in bed like a stepped-on rake. The mockingbirds had gone back to regular hours.

Research has shown that mockingbird males, like songbirds everywhere, sing to attract mates and to advertise territorial boundaries--during the day--but unlike most birds, they also sing at night for hours on end during the spring and summer. This piqued my curiosity. I was trained as a biologist, and while no longer doing "official" research, I am not above a speculation or two or even a simple, easy-to-do experiment. The results and the conclusions can be provocative and can also run counter to folklore. Mockingbirds, for instance, are not singing out of joy or pleasure as is commonly believed. Much of the time, they sing out of desperation.

During the past summer, a pair of mockingbirds took possession of the tree next to my office window. Their property included my neighbor's entire backyard, along with the back half of the woman's on the other side of the block--and a choice property it was. The lawn looked like a putting green; the garden was lush with tomatoes, squash and zucchini, and the place was circled with a variety of thick, healthy shrubs and trees. It was also paradise for the insects on which mockingbirds make their living.

I had been working late one night in July, and at around 2 a.m. it suddenly occurred to me that Jack, as I called the male of the family, was becoming rather obnoxious. He had been singing without pause for at least an hour, and as the night wore on, his volume was rising. Maybe because the background noise was quieter his voice just seemed louder, but the fact was, my ears were actually fluttering with the sharp, choppy, ragged phrases that mockingbirds like.

But why was he singing at night in the first place, when most species of birds simply sleep? It was hard to make biological sense of it. For one thing, he was giving away his position to every cat on the block. Second, all that volume was generated by the laborious convulsions of Jack's diaphragm and breast muscles, and the work took energy. Birds the size of Jack sometimes eat twice their body weight each day to pay the cost for warm blood, and, on top of the usual worries of survival, Jack and his mate, Jill, were rearing some very hungry chicks. Jack and Jill were locked into the frantic pursuit of energy, which is what life amounts to, and here he was blaring forth all night long. No bird would spend that kind of energy unless it was critically important.

"I wonder," I thought, "if this racket drives cats away ?" It was plausible. But no--it couldn't be a defense because if that were so, all birds would have hit upon the secret and would be singing at night. The din would be stupefying. No--the only reason I could see had to be competition with other mockingbirds. And that would be easy to test.

I set a tape recorder in the window and began recording. Half an hour later Jack stopped for a breather, maybe even a nap. Not, however, if I could help it. I rewound the tape and turned the volume up.

"Chireep, chireep," went the tape.

" Chireep! Chireep! " erupted Jack not a second later.

"Rash, rash, rash," went the tape.

" Rash! Rash! Rash! " screamed Jack.

"Tweedle, tweedle, tweedle."

" Tweedle! Tweedle! Tweedle! " gurgled Jack, almost strangling in frustration.

He was reacting not only to a recording of a song he had sung no more than 30 minutes earlier but also to each phrase. In his little bird's brain, he was being challenged by a monster stud, and by the gods and the bushes and the bugs, he was not going to go quietly.

The evidence clearly suggested the kind of life a mockingbird lives. Like most songbirds, they have evolved a system of parceling up the land, which acts as a kind of natural farm, with the males defending the boundaries. They rarely fight physically, though, presumably because injury is too costly at a time when a bird needs all its strength just to break even in the energy economics of life. But there is usually no need to fight, because the vigor and skill of your song gives a good idea of the vigor and skill of your body--should a little more convincing be necessary.

The odds are that Jack was locked in musical combat for his family's survival. And singing was the measure of his substance and grit. If he got sick or injured, or old, that would also come out in his song, and his neighbors would probably start to encroach. Annexing part of Jack's land could make the difference between rearing maybe two chicks or as many as four.

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