Tweets,

One other possibility to account for the mid-winter Barn Swallow mystery,
perhaps fanciful, is that they "hibernate," waking up to fly around and feed
a bit when the weather is particularly nice. This was fairly recently
demonstrated for Poorwills, who were found in a state of "suspended
animation" in mid-winter in southern Oregon. It may be true for hummingbirds
and swifts. I understand this is not true hibernation, but a state of
semi-dormancy. Perhaps the Barn Swallows were snoozing happily in some
sheltered spot all along?

Gene.

----- Original Message -----
From: "Ruth Sullivan" <godwit at worldnet.att.net>
To: <tweeters at u.washington.edu>
Sent: Monday, January 21, 2002 9:39 AM
Subject: Fw: Winter swallows and other passerines


>
> ----- 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
> >
>
>