Thanks to shorter days and chilly morning temperatures, curious naturalists know the transition from summer to fall has begun. Various fall migrations also provide evidence that autumn is coming.
Chimney swifts are familiar summer residents. They spend all day sweeping the sky for flying insects while twittering incessantly. At a glance, they resemble flying cigars. Swifts are common in towns and cities where chimneys are seldom in short supply.
They winter in the upper Amazon basin of Peru, Ecuador, Chile and Brazil. At dusk, swifts assemble and descend en masse into chimneys where they roost for the night.
Hundreds or even thousands may roost in abandoned industrial chimneys. Residential chimneys may host a dozen or more.
Something to see
The swifts’ descent into a roost site is a sight to behold. Sometimes a flock circles for 15 to 20 minutes before one bold soul breaks from formation and dives into the chimney.
Others quickly follow. If the flock is large, the image suggests a plume of smoke returning to the chimney. Swifts are flying machines.
Their long, narrow wings enable rapid, agile flight. They descend into chimneys headfirst, then flip tail-first once inside.
There they perch by clinging to the vertical wall. All four toes on each foot are directed forward so they can cling tightly to rough, vertical surfaces.
Their tail feathers are tipped with stiff spines that stabilize them while roosting. But because they lack a hind toe, they cannot perch or walk as most birds do.
As swifts begin their migration to South America, watch for dwindling numbers where they’ve been common all summer long.
Another expert flyer that will soon head south is the common nighthawk.
Kin to whip-poor-wills, nighthawks frequent open country, towns and cities. I look for them at the first few high school football games of the season. High above the action on the field, nighthawks swirl around the stadium lights catching their fill of flying insects attracted to the lights.
Shortly before and after sunset, I’ve counted as many as 20 nighthawks feeding above the action on the field. I watch until they disappear in the darkening night sky.
It’s another reason to always take binoculars to late summer sporting events. About the size of a robin with longer, narrower wings, nighthawks are charcoal gray with a single bold white bar on each wing.
The wing bars are so obvious they can sometimes be seen with the naked eye. Hummingbird action at nectar feeders has begun to slow, and that’s a sure sign that their migration has begun.
In mid-August, ten to 15 hummers drained my feeders every day. Now I count just four or five at a time, and feeders take up to three days to empty.
By late September, most hummers will be gone, but keep one feeder up until mid-October for stragglers moving south from farther north.
And don’t worry that maintaining feeders well into fall will deter hummers from heading south. They respond to shorter day length, not food supply.
Monarch butterflies have also begun their southbound journey to the mountains of central Mexico.
Watch for groups roosting on trees and shrubs at the end of the day. Those flying purposefully south 20 to 50 feet above the ground during the day are answering a call we are just beginning to understand.
Songbirds migrate south under the cover of darkness, so observing this must be done indirectly. Step outside after dark over the next six weeks, and listen for 15 minutes.
Chances are good that you’ll hear nocturnal flight calls that help keep members of migrating flocks together.
And on nights when the moon is almost full, scan it with binoculars or a spotting scope.
Watch for 15 or 20 minutes, and you will almost certainly see a few birds crossing the face of the moon. Then try it again a day or two before and after the next full moon Sept. 27.
There’s no doubt about it. Fall migration has begun.
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