Every year about Oct. 1, I start watching. Birds of course react to temperature and climate conditions, especially wind. In general, though, they migrate not according to weather but according to the sun, specifically to length of day. Even though warm weather lets us imagine we're still clinging to fall, the sun sets earlier and rises later, giving us now just under a 12-hour day. Somehow, birds register those subtle changes. They know it's time.
During the past weeks, several weather fronts passed through, some stronger than others, most accompanied by northerly breezes, the perfect impetus for birds that know it's time to fly south. They love energy-saving tail winds.
Next morning, yellow-rumped warblers, ravenous after another leg of their series of overnight flights, dropped in for a welcome-back drink and refreshing dip, then berry picked in the common beautyberry bush. Like the white-throat, the yellow-rump has come for the winter.
Strong winds the night of Oct. 1 forecasted dramatic change the following day. Indeed, the forecast materialized with the arrival of birds we hadn't seen in six months: ruby-crowned and golden-crowned kinglets and pine siskins. They arrived to settle in as other migrants, facing hundreds of miles yet to go, prepared to move on.
So it was that during 12 crazy minutes that morning, we tallied a whole range of tropical migrants joining the four just-arrived overwintering species: three rose-breasted grosbeaks, three each Tennessee and Nashville warblers, one each magnolia and black-throated green warbler, two gray catbirds, and 18 hummingbirds. Then, after 12 minutes of craziness, the yard went quiet and stayed that way for the day. Wish I understood how that happens.
Of course, given that white-throats and siskins have arrived, can juncos be far behind? The bird my grandma called snowbird, because, she said, it brings the snow with it, usually arrives by October's end. This year, however, our first arrived Oct. 4--begging the question: Can snow be far behind?
That's how fall migration works: Winds that push tropical nesters out simultaneously push overwintering birds in. Certainly not all birds of a species leave or arrive at the same time. A few hummers linger. Tardy warblers forage. Migrants don't travel in flocks so migration stretches across weeks. When a strong front blows through, overlap often occurs. Thus, only now can we see--and hear-- all these birds on the same day in the same place, a magnificent once-a-year migration phenomenon.