Feb 28 2009
At this moment there are chipping sparrows feeding on the ground outside my window. And I can hear the “chucking” call of a nearby common grackle. Otherwise, no birds on the feeders. A quiet morning.
Birds are an interest of mine. When you combine birds with science, well, my cup runneth over.
Ooh. Female cardinal. A male flew in and she bolted. He’s feeding, peeling seed husks from the seed, making teet!-like calls every three seconds or so. Didn’t his mother instruct him not to sing with his mouth full?
In research on Savannah sparrows conducted by Heather Williams (rhymes with feather — sorry) of Williams College that I encountered three items I’d like to share and comment on.
1. Whose Theory is It?
From what she has gathered so far, she says that “singing doesn’t seem to be the basis of mate choice by females.” There doesn’t seem to be a particular kind of song that appeals particularly well to females, nor does seem to matter how well or how cleanly a male sings his song.
The way singing functions in bird society “doesn’t seem to be simple,” Prof. Williams said. It raises the question: What is the point of singing in the first place? If further research confirms these early observations, she believes it may lead to a refinement of Charles Darwin’s theory of sexual selection. Darwin wrote that that the differences between the sexes in a species evolved either to compete for or to attract mates. But that idea has had to be expanded more recently to account for research on cooperative behavior.
So the singing may not play a central role in sexual selection. Instead, perhaps it has something to do with an individual’s fitness to a niche that includes social relations. Does this mean there is no sexual selection going on? And would findings like the above lead to a refinement of Darwin’s theory, a refutation of some of his thinking, or an advancement in modern evolutionary theory?
2. Learning to Sing
Previous generations of birdsong researchers have shown that birds learn their songs in ways very similar to the ways human infants learn language. They start with a period of close listening, followed by a “subsong” phase akin to human “babbling,” as they work out the phonemes they can physically make and map the sounds to the motor skills it takes to make them, “to calibrate the vocal instrument,” as Prof. Williams puts it. After that comes the “plastic song” phase, when they begin to put the parts together in imitation of models they’ve heard, and a “crystallization” period when they settle on a tune that works.
Cool. The question is – How does the tune work? What does it accomplish? Maybe it doesn’t impress potential mates. Might the song be a tool with a multitude of functions?
3. Cuckolded by a Sparrow
In some ways, it can seem like a very complicated episode of “Melrose Place.” One particular long-lived male is known as “S.RN,” so-called because his left leg has a striped band, and his right leg a red band over a navy blue one. In 2004, he mated with five different females, and raised 20 nestlings. Subsequent blood work revealed that only 16 of them were actually his offspring (he didn’t lose much overall, because he fathered at least five that hatched in other males’ nests). More importantly, four of his offspring returned to breed the next year — a good result as usually only one in ten return.
Now I’ve got a dozen goldfinches on the feeders, one female cardinal, and a bunch more chipping sparrows. I wonder if any of the sparrows or finches are past “lovers.”
Although we are learning more, we still know so little about bird behavior.