Birding Notes

Reflections on birds and other wildlife on the edge of a southern woodland

Friday, May 22, 2009

Trio-flying Chimney Swifts

Late this morning three Chimney Swifts passed low over me, flying close together and twittering loudly and constantly, with stiff wings fluttering. They swept through the trees and down over open grassy yards, then streaked back up again high, swooping over me several times while I was walking, always twittering and flying fast, diving, climbing, and weaving in and out of trees.

This “trio-flying” is a common behavior of Chimney Swifts at this time of year – something I have noticed in the past and sort of halfway wondered about, but never took the trouble to learn more about or question until now. There was something about their constant, expressive twittering calls that made me stop and watch them more closely this time, and the fact that they swept so low and in such dramatic patterns – quite different from the way they might pass over much higher on a lazy summer day.

The Birds of North America species account says trio-flying seems to be performed by one female and two males. Its function is not known, though apparently it’s a part of aerial courtship displays early in the season. It’s “characterized by three swifts following each other as they thread their way among buildings and trees, with incessant, louder-than-normal Chipper Calls . . . At peak intensity, trio-flying results in the most rapid flight speeds, ascending to much greater heights than normal, and flying horizontally great distances.” *

Learning about “trio-flying” is another reminder to me of how much I often take for granted – how much there is to learn about things I see and don’t think to question, or to really watch and listen carefully and with an open mind.

In the course of looking for this information, I also discovered an interesting description of Chimney Swift voices by Winson Marrett Tyler, in A.C. Bent’s Life Histories, which reveals that what I’ve always heard as just a rather nondescript “twittering” actually consists of a surprising variety of calls, though I have to admit it’s hard to imagine hearing these variations in the rapid-fire chatter of the birds as they pass so quickly overhead.

“The notes of the swift remind us of the bird itself – energetic and quick; sharp and hard like the bird's stiff wings,” Tyler wrote. “The note most commonly heard as the birds shoot about over our heads is a bright clear, staccato chip or tsik – whichever suggests the sharper sound – often repeated in a series and sometimes running off into a rapid chatter. . . . Simple as these notes are, the birds introduce a good deal of variety into them by modifying the interval between them, thereby changing the expression of their lively theme.

“One modification . . . serves to illustrate this ability and may be regarded as representing the song of the swift. It is made up of a long series of notes in which the birds, after giving several isolated chips, change abruptly to a series of very rapid notes, a sort of chatter, then with no pause between, change back to the chips, then back again – chips – chatter – chips, and so on. We may term it the "chips and chatter call.". . . Another modification of the chip note, often heard in summer when the birds are in a comparatively quiet mood, is a long chatter in which the volume increases and lessens, suggesting the sounding of a minute watchman's rattle.” **

*Calvin L. Cink and Charles T. Collins. 2002. Chimney Swift (Chaetura pelagica), The Birds of North America Online (A. Poole, Ed.) Ithaca: Cornell Lab of Ornithology.

** Winson Marrett Tyler, Chimney Swift (Chaetura pelagica) in Life Histories of Familiar North American Birds. Arthur Cleveland Bent, 1940, United States Government Printing Office. Selected and edited for online publication by Patricia Query Newforth, 1996-2009.


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