Saturday, October 16, 2010

Chimey Swifts

A squadron of Chimney Swifts rockets overhead. These interesting birds are far more at home on the wing than they are grounded. In fact, a Chimney Swift cannot perch, at least in a conventional manner. Their genus name is Chaetura, and that means "bristle tail". Stiff spiky feather shafts project from their tail feathers, and the birds use them to prop themselves upright against the roughened inner wall of a chimney, or hollow tree.

During last weekend's excursions into Dike 14 (see this post), our groups were dumbstruck by the sheer numbers of swifts coursing overhead. I attempted many photos, and had I been alone I would have spent far more time tying to make photographs of the little feathered rockets. It isn't easy - these scimitar-shaped missiles move FAST, even when they appear to be loafing.

Nothing, and I mean NOTHING, that human aeronautical engineering has yet devised comes close to matching the aerial prowess of a swift. Note the wing to body ratio of the birds in the above photo. That is the profile of a beast made for flight. Each square inch of wing surface equates to less than a gram of body weight. For a Boeing 727 airplane to attain that ratio, it'd have to have wings nearly eight miles long, and not gain any extra weight.

A swift is a true sky-surfer; possibly more at home in the blue ether than any other type of animal. They drink on the wing; eat on the wing. Court on the wing, showing off in rapid glides with wings held stiffly upwards in a V-shape. Swifts even consummate their relationship while airborne and that's a feat, I'm sure.

It's been shown that at least one species, the Common Swift, Apus apus, of Europe, even sleeps on the wing! Common Swifts don't reach sexual maturity until their second year, and once one bails from the nest, it might not alight again for two years. With the onset of dusk, the swifts circle higher into the sky, and essentially enter a circular holding pattern, dropping back towards earth with morning's light to commence feeding on flying insects.

Aerial roosting has not been documented with our species, the Chimney Swift, insofar as I am aware. They are well-known for forming sometimes massive roosts in favored chimneys, and the spectacle of the birds dropping into the maw of the chimney at dusk often lures crowds at famous roost sites. However, my observations over several years at Dike 14 make me wonder if they do sometimes sleep on the wing, like Common Swifts. There is no question that Dike 14 is an important stopover site for migrant swifts. Early to mid-October sees flocks of hundreds concentrated directly over the Dike's lush greenery; this habitat no doubt sends lots of insects aloft to be snagged, and perhaps creates thermals that aid the birds' flight.

Several times now, I've been at Dike 14 before the sun slips above the eastern horizon, and watched and heard clouds of Chimney Swifts high above, descending as the day lightens. Where would they be coming from? It doesn't seem likely that all of them had already escaped the confines of roosting chimneys somewhere in Cleveland, and made their way out over Dike 14. I wonder if they, like their European counterpart, spend their evenings over this migratory waypoint high in the air, circling like tiny aircraft placed in limbo by the control tower. I'd think they would certainly be capable of aerial roosting, and wonder if that isn't a more efficient way to spend the evening in certain situations.

Surprisingly little is known of Chimney Swifts, even though they are a common bird in these parts. It's hard to study them. They're creatures of the sky and we're largely land-locked. It won't be long and our swifts will be long gone, skating their way well to the south, to disappear into the tropics of the Amazonian basin and South America. There, nearly nothing is known of their activities. Dike 14 is certainly more accessible and I'd love to know whether the migrant swifts that frequent this place truly do sleep on the wing. If they do, it'd be just another bit of a fascinating puzzle unraveled.

1 comment:

Helen Ostermiller said...

Jim, we watched hundreds of swifts over Chippewa Lake in Medina County and the woods and fields adjacent this fall. We estimated 500 last weekend, when you watched those over Dike 14. By this weekend, ours were gone, leaving tree swallows over the lake.

We haven't looked for a roost in the nearby community, though we've talked about the possibility. Your post makes that information even more interesting. Now we have a job to do next year!