When I lie awake in the twilit pre-dawn hour and listen to the chorus of birds — the large heavy branches of an old Douglas fir are just outside my second-story bedroom window — not only do I curse my wakefulness but also wonder at the concert being performed for, well, it seems to be for only me. (One of the few conceits I stubbornly maintain.)
Wonder, to be more exact, at the how of their volume from such creatures of insubstantial heft. If I could roar at a volume proportionate to my, ahem, heft at the same ratio of birdsong to bird, well, I'd be in violation of a city law.
After a brief investigation, I learned that birdsong originates from the syrinx, a sound producing organ, which is situated at the junction of two bronchi leading from the lungs. When air from the bronchi passes over the syrinx, vibrations occur, producing what we recognize as song. But even better, each bronchus may produce a separate tone, which is then "mixed" as it passes over the syrinx, resulting in the many-toned and elaborate "songs" which entertain my early waking.
It is theorized that birds produce this prodigious amount of song at dawn because that is the best time for sound to travel, there being little wind or other noise disturbances. Another theory is that male birds may just be boasting their virility despite their typically low energy reserves after a night of no feeding. (Men!)
Science aside, I remain in rapt awe of the complex structure of these songs, both rhythmically and tonally, an olio of sound that includes robins, house finches, sparrows, wrens, bushtits, jays and nuthatches.
Here's a short recording of a house finch singing. After listening to perhaps a dozen of these on YouTube, I chose this one for the commentary in the background — a snippet of birdsong but also a snippet from a stranger's life —