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IN THE FIELD: Common nighthawk

Common nighthawks have one of the longest migration routes among North American birds, wintering all the way in South America.

We now find ourselves squarely in the downswing of autumn, though it feels like I must have blinked and missed something. Just a few weeks ago the yellow-rumped warblers, probably the most abundant of the migrating warblers, were coming through in hordes, so ubiquitous at certain points during fall migration that I can easily distinguish their call note from the call notes of all other warblers, because I’ve grown so accustomed to it.

But now it finally feels like November. The geese are shifting around and waterfowl are migrating through, and sparrows are the mainstay of a backyard — I wake up to the sounds of song sparrows, and the clear whistled notes of white-throated sparrows, winter residents returned from the north. Juncos are here, too, their white-edged tails flashing, and we can feel winter coming.

There are still plenty of birds out, of course. In fact, the warmth this month seemed to animate them, and there was so much chirring and chirping it almost sounded like spring. Mockingbirds were singing regularly, and I’ve heard the distant commotion of what must be massive flocks of red-winged blackbirds congregating in the cornfields. Birdcast’s migration forecast tells me that the last of the blackbirds were coming through last week, and also that rusty blackbirds, a much rarer species, are also having a strong flight, so perhaps I should check the flocks in search of that blackbird I’ve never knowingly seen.

Birds do sing in the autumn; it’s not entirely unusual. Various factors seem to be at play — the birds may sing to maintain the social structure of the flock, or to establish winter or feeding territories. Juveniles may be learning and rehearsing their songs, but perhaps the Indian summer intensified their activity.

All the warm spells had me thinking of summer, and I found myself returning to one of the last summer spectacles I witnessed, sometime in late August. Early one sunny evening, while parked on the side of a busy road, I noticed several common nighthawks darting and swooping around me. On their sleek pointed wings, they rode the air the way surfers ride waves, turning in wide arcs above my head as they feasted on columns of insects.

At first I was impressed that there were eight, but then I looked farther down and realized that the air was teeming with them. Some were low, right above my head, the white blaze on their wings clearly visible, but others were just specks. Probably well over a hundred nighthawks, along with swallows, scoured the late afternoon air above the highway that day.

Late summer migrations of nighthawks in the Northeast traditionally consisted of hundreds at a time, but they have been declining since the ’80s. A couple of years ago I wrote about a State of the Birds report from Connecticut Audubon, which focused on birds like nighthawks that feed on the wing — aerial insectivores. Based on years of data, scientists noticed that they were declining more precipitously than other species, and especially in the Northeast, but no one really knew why. These different families of birds — swallows, swifts, flycatchers — were united by their reliance on the drifting masses of flying insects in “the seventh habitat,” the air above the earth.

Insect abundance could be affected by pollution, pesticides, or changes in weather patterns, as could the birds themselves. Milan Bull, a scientist with CT Audubon, recently told me that “the jury is still out” regarding the cause of the declines. It is likely a combination of factors.

Common nighthawks have one of the longest migration routes among North American birds, wintering all the way in South America. That report had also noticed that species of aerial insectivores who were long-distance migrants were declining more sharply than short-distance migrants. Again, no one knew why. More indiscriminate pesticide use in Central and South America was one theory, but in any case, it makes one consider the feat of migration, and the hurdles birds face along the way.

Where are those hundreds of nighthawks that I saw now? November eBird sightings show the species clustered around Central America, with many already in South America. We may be adjusting our mindsets to autumn and winter, but “our” summer birds are still out there, still on the move, eking out their survival just the same.

The Cornell Lab of Ornithology has prepared this recording of nighthawks:

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