Subject: Fw: Winter swallows and other passerines
Date: Jan 21 13:36:07 2002
From: Scott Atkinson - scottratkinson at hotmail.com


On the Barn Swallow sightings this winter:

Although I'm as puzzled as others on this year's remarkable winter Barn
Swallow count, I like the reminder that this is in fact a mild winter so
far. I noted in the Townsend's Warbler discussion that we've yet to drop
below 25 F. here in outlying Lake Stevens, and in the city I doubt it's yet
been much below 30-32. Still, as a counterpoint, I would bet that the
average mean temps at Sea-Tac Arpt for November and December 2001 would not
be greatly above the norms (45 F and 41 F respectively).

Still, I like the notion presented that the swallows might have "simply
stayed here" as another potential explanation, although it's hard to figure
how so many Barns could have been overlooked during area CBCs. Dennis'
flock up at Everett could have been missed on the Everett CBC Dec. 15, given
the wretched weather we had. And both wWa and s.w. coastal BC seemed to
have a better-than-average fall for late swallows (including others than
Barn), and, although we've had wintering Barns before, I don't ever recall
this many reports--in any year--previously.

Scott Atkinson
Lake Stevens
email: scottratkinson at hotmail.com

















>From: "Ruth Sullivan" <godwit at worldnet.att.net>
>Reply-To: godwit at worldnet.att.net
>To: <tweeters at u.washington.edu>
>Subject: Fw: Winter swallows and other passerines
>Date: Mon, 21 Jan 2002 09:39:56 -0800
>
>----- Original Message -----
>From: Joel Geier <jgeier at attglobal.net>
>To: Obol <obol at lists.orst.edu>
>Sent: Monday, January 21, 2002 9:38 AM
>Subject: Re: Winter swallows and other passerines
>
>
> > Hello OBOlers,
> >
> > This has been an interesting discussion, and I have not
> > noticed anyone trying to claim that there is a single,
> > simple answer to the puzzle.
> >
> > In the interest of avoiding oversimplification, I suggest we
> > should disabuse ourselves of the notion that there is
> > "nothing special" about this year's weather. The average
> > daily low temperature data I cited yesterday show that this
> > is one of the six mildest winters in the mid-Willamette
> > Valley, out of the past 40 years. Beyond that, there has
> > not been even a single day of sustained freezing weather --
> > the lowest daily high temperature so far at Corvallis
> > (Hyslop field station) was 39 deg F.
> >
> > In other words, this is clearly a notably (if not
> > freakishly) mild winter. While I agree with Dave Irons and
> > Phil Pickering that this may not be a primary cause for
> > unusual birds to show up in our area, it certainly needs to
> > be considered when pondering why unusual birds are being
> > observed.
> >
> > As Irons points out, the reason why various passerine
> > species have occurred in our area likely varies from species
> > to species. Some like the Hermit Warblers are presumably
> > lingering birds (or birds whose migration from a bit farther
> > north in their breeding range was for some reason
> > abbreviated). The eastern vagrants may have shown up here
> > due to a flip of their "magnetic compasses." The Barn
> > Swallows might be getting pushed north into our area on
> > sustained southerly winds -- well, maybe. All of these are
> > fine explanations (some more speculative than others) as to
> > why these birds arrived or simply stayed here.
> >
> > Irons rightly points out that "year-to-year weather patterns
> > probably affect nothing other than the survival rates" of
> > semi-hardy passerines. I would add that weather patterns
> > also affect detection rates: To be observed well into the
> > winter months, the birds first need to survive. That's
> > leaving aside the intangible effect of weather on observer
> > activity.
> >
> > In the same vein, Steve Mlodinow points out, "When a Barn
> > Swallow wanders a thousand miles north of its normal winter
> > range, it is in a very tenuous position. It is hard to
> > imagine that these birds are not doomed." Unless, of
> > course, they find that unusually mild temperatures have kept
> > an adequate supply of their usual forage on hand.
> >
> > Regarding the "pineapple express" theory for Barn Swallow
> > occurrence, the absence of Violet-green Swallow reports and
> > sparseness (within normal ranges) of Tree Swallow reports
> > does raise some problems. As Mlodinow suggests, one might
> > logically expect these more northerly wintering swallows to
> > be pushed north by the same prevailing winds, and to arrive
> > in numbers ahead of the more southerly wintering Barn
> > Swallows.
> >
> > Let me throw out another word: DISPERSION. When a
> > population of birds starts to move north (with or without
> > the help of prevailing winds), a few birds generally arrive
> > well in advance of the main horde, and then we see a steep
> > ramp-up as the main population arrives. Think of the spring
> > arrival of Violet-green Swallows -- for a few days we get
> > scattered reports, and then suddenly, one day they seem to
> > be everywhere.
> >
> > A similar phenomenon is seen in the study of how chemicals,
> > colloids, bacteria etc. spread out as they migrate along
> > with groundwater currents. In that field the process is
> > called "dispersion" (Probability freaks may be entertained
> > to know that the shape of the curve is the classical
> > Gaussian error function). Mathematically it can be shown
> > this phenomenon is the natural outcome of combining small,
> > random movements of itty-bitty things (whether birds or
> > bacteria) in a prevailing current (water flow, prevailing
> > winds, or the "migratorial urge").
> >
> > I would argue that what we have seen so far does not look
> > like anything like the "dispersion front" associated with a
> > northward movement of a Barn Swallows population. Apart
> > from two instances of small flocks (8 birds and 15 birds,
> > each seen on one day only), all other sightings have been of
> > 3 birds or fewer. If a sizeable population is being pushed
> > north, at some point we should see more than the dispersed
> > fringe, but it hasn't happened yet. Here in Oregon, the
> > Yaquina Bay flock on 5 Jan was not followed by numerous
> > flocks in the following week. Instead we went back to the
> > pattern of a few individuals seen here or there, which had
> > been the pattern through most of December.
> >
> > If tomorrow we start getting reports of Barn Swallows
> > everywhere in western Oregon, that would add some credence
> > to the northward-drift theory -- but we haven't seen that
> > yet.
> >
> > I would also argue that a bit of a reality check is called
> > for regarding the "sudden occurrence" of Barn Swallows.
> > There have been a few unsupported statements made about
> > this, e.g.: "After an apparent absence in late Fall and most
> > of December these birds have suddenly appeared." This seems
> > to be based more on sudden attention to Barn Swallow
> > sightings since those notable flocks in Newport and Everett
> > were reported, than on a full consideration of sightings in
> > the early part of the winter.
> >
> > If you look at a nominally unbiased record of sightings
> > since late fall, the grounds for such statements are rather
> > scant. Here's the full set of actual & possible Barn
> > Swallow reports from the "OBOL reporting area," since the
> > tail end of fall migration:
> >
> > Date No. Place (observer)
> > 29 Oct 1 Scravel Hill pond, Albany area (Marcia
> > Cutler).
> > 1 Nov 5 Ankeny NWR south of Salem (Roy Gerig)
> > 2 Nov 8+ Ankeny NWR (Jeff Harding)
> > 9 Nov 1 Barn near Ankeny (Stuart Sparkman)
> > early Dec "several" Monmouth, OR (Maggie Meikle)
> > 11 Dec 2 Smith & Bybee Lakes, Portland (David Bailey)
> > 14 Dec 2 Smith & Bybee Lakes, Portland (Tom Ewert)
> > 17 Dec 1(*) Fern Ridge Reservoir (fide Harry Nehls)
> > 28 Dec 1 "regular" at Hansen NWR (Mike Patterson)
> > 30 Dec 1 Hansen NWR (Mike Patterson, Russ Copenheim)
> > 3 Jan 1 Near Shedd, mid-Willamette Valley
> > 5 Jan 8 Yaquina Bay South Jetty (where did they go?)
> > 6 Jan 3 Livermore Rd., Polk Co.
> > 13 Jan 1+ Steigerwald NWR, WA (Pamela Johnston)
> > 14 Jan 1 Monmouth, OR (Maggie Meikle)
> > 14 Jan 1 Amazon Cr, Fern Ridge area (Dave Brown)
> >
> > (*) Reported as "Swallow sp.," may not have been Barn
> > Swallow.
> >
> > The only gap in the above is from 10 Nov to "early" December
> > (whenever that might have been). As I recall, that was a
> > time of near-continuous rain in our area. Was the level of
> > birder activity comparable to that in the CBC season, or in
> > the couple of weeks of relatively clear weather since then?
> > And even if birders were out, might not swallows have been
> > hunkered down somewhere or just plain missed, considering
> > the rain? Given that the numbers observed outside of that
> > period have been scant (except the one flock), it seems
> > probable that these few individuals could just have been
> > missed during that period of rainy weather. The fact that
> > the Newport flock was seen on only one day illustrates that
> > swallows can indeed hide from us.
> >
> > This is not to say the "pineapple express" theory might not
> > be at least part of the explanation for why a few Barn
> > Swallows are being observed. However, I'd caution that the
> > evidence of a dramatic change since the start of the year is
> > exceedingly thin. Let's wait and see what this week brings
> > .... which I guess means going outside for a look!
> >
> > Good birding,
> > Joel
> >
> > --
> > Joel Geier
> > jgeier at attglobal.net
> >
>
>


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