I was awakened at 6:30 this morning by what sounded like a young house finch learning to sing, just outside my window. It got me thinking.
Every fall, songbirds which have stopped singing during high summer start up again, briefly, to sing for a few weeks before weather gets cold. A discussion several years ago on a local birding list concluded that nobody knows for sure why birds sing in autumn -- are they confused about the weather and think it's spring again, hoping for a last fling before the cold weather sets in, or what? There's a a wonderful ditty about it, "The Autumnal Recrudescence of the Amatory Urge", apparently written in the 1970s by Susan Stiles.
It's too early in the year right now for autumnal anything -- it's still quite warm. But lying there in bed listening to the exploratory notes of a bird clearly not yet confident in his song, I got to thinking about how birds learn their songs.
In most birds it's not innate: young male birds learn singing while still nestlings from listening to their father sing, much like human babies learn the rhythms of their native language from hearing their parents talk; and if you raise a songbird in a nest of another species, they will often learn the wrong song, or end up with some hybrid song that doesn't attract females of either species. (A good overview: The Development of Birdsong on Nature.) More recently, there have been all sorts of interesting studies on how young birds learn their local dialect, since a species' song varies quite a bit from one location to another.
But ... not all birds sing much once the eggs are laid, do they? They sing their hearts out while acquiring a territory and trying to attract a female; but once nesting starts, I don't remember hearing much activity from the house finches. Mockingbirds are an exception: I've seen mockers singing day and night even after they're feeding nestlings, though not all male mockers are quite so industrious. But I thought most species stopped singing much once the nest was built and eggs laid.
But if that's true, when do the young males learn their songs? Even if the father does sing a little, off and on, while the nestlings are being raised, that's not very much time to learn. Suppose the adults started singing again in the fall before the family disperses. Wouldn't that be an advantage to the young males who are just learning their songs? If a fledgling, off the nest and mostly able to care for himself, is "babbling", trying exploratory notes while learning what sounds he can make, wouldn't it be helpful to have a few nearby males who occasionally burst into song even if it's out of season?
Maybe the "Autumnal Recrudescence" isn't birds being confused about the weather at all. Maybe it's an evolutionary aid to help the young birds crystallize their songs before heading into their first winter. By singing in autumn, the males help their sons crystallize their songs for the next year, which helps the sons be more successful when it's time to look for a mate next spring.
Just a theory ... but I think it makes some sense, and I'll be listening
to this autumn's chorus with new interest.
[ 11:57 Aug 18, 2013 More nature/birds | permalink to this entry | comments ]