Hello, All.
(Nice night flight in the 1am hour this morning, Friday, Sept. 3, over
Lafayette, Boulder County, Colorado. First good push of presumed
Orange-crowned Warblers, which migrate much earlier in fall in Colorado
than in, say, Ithaca, New York. Wilson's Warblers continuing, too, and
Chipping Sparrows--presumably mostly juveniles now. Anyhow...)
===
As I think a lot of us know, Barn Swallows give an amazing variety of
vocalizations while on the wing. They can sound like Solitary
Sandpipers, they can sound like Scarlet Tanagers, they can sound like
House Finches, they can sound like Lark Buntings, they can sound like
Bullock's Orioles, and on and on and on.
At least here in Colorado, Barn Swallows fly by night and are
exceedingly vocal. Unquestionably, I hear far more Barn Swallows by
night in Colorado than any other bird species, from mid-July into early
September. These are birds high overhead, calling almost constantly. In
mid-July, I assume these are mainly or entirely local birds just
socializing at night. The Barn Swallow just happens to be an especially
active night-calling passerine. (Other passerines that are vocal by
night on the breeding grounds in Colorado include Cordilleran
Flycatcher, Violet-green Swallow, Sage Thrasher, Yellow-breasted Chat,
and Cassin's Sparrow.)
Broadly speaking, then, the following statement from the Evans & O'Brien
CD-ROM needs to be updated: "Primarily a diurnal migrant. May migrate at
night in spring in the Gulf of Mexico region. Flight calls are given
regularly by perched and flying birds during the day. Not known to give
flight calls at night." Again, and just to beat a dead horse, I hear
more nocturnal flight calls from Barn Swallows than from any other bird
species.
But what about the more nuanced question of Barn Swallows on active
nocturnal migration? First, do they migrate by night? And, second, if
so, what do they sound like?
Well, I've been wondering about that a fair bit. Given that Barn
Swallows are flying around at night anyhow, often quite high up, and
well away from roosts and nest sites (e.g., high above lakes and pine
forests), mightn't they also be nocturnal migrants?
So here's my hypothesis. The flight call given by Barn Swallows on
active nocturnal migration seems to be what Evans and O'Brien call the
"vwit" call. That is the call I hear from birds that I judge to be
moving north to south on nights when other expected species are on
nocturnal migration. It's a rising flight call, with 3 or more "bands."
If you have the Evans and O'Brien CD-ROM, it's this one: Flight
Calls\SPECIES\SWALLOWS\BARS\BASWVAR.HTM
The problem is, Barn Swallows make me nervous, ID-wise. Is the Barn
Swallow's "vwit" call distinguishable from the flight calls of Bobolink
(presumably a rare migrant where I listen), Bullock's Oriole (common
migrant here, but most movement appears to be diurnal), Lark Bunting
(distinctive flight call, but, I swear, some sound like Barn Swallows!)
or even House Finch (notoriously variable, and who's to say they don't
move at night?). I'm not so sure. But here's what I can say: Barn
Swallows are extremely vocal, on the wing, at night, at least in
Colorado, and that's a broad pattern, something I've noticed all across
the region; their "vwit" call is certainly one I hear a lot of; and it
seems to be the call of birds on active nocturnal migration; but we need
to be aware of (at least, I need to be aware of!) the possibility of
confusion with other birds with rising, multi-banded,
fairly-low-frequency flight calls.
In other words, next time you think you're hearing orioles or Bobolinks
or Lark Buntings or something, be aware of the possibility of Barn
Swallows, certainly on the wing by night, and quite possibly in the act
of active nocturnal migration.
---
Ted Floyd
Editor, Birding
Follow Birding magazine on Twitter: http://twitter.com/BirdingMagazine
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