[obol] Early Swainson's Thrush reports
- From: "Wayne Weber" <contopus@xxxxxxxxx>
- To: "OBOL2" <obol@xxxxxxxxxxxxx>
- Date: Sun, 27 Apr 2014 09:13:35 -0700
Dave,
Thanks for your long and detailed discourse on early spring reports of
Swainson's Thrush-- delivered in your usual eloquent fashion. What you said
needed to be said. From my perspective in and around Vancouver, BC, I deal
with much the same problem. Every year, as the Vancouver regional editor for
eBird, I deal with numerous April reports of Swainson's Thrush, nearly all
of which are questionable. Most of these are probably misidentified Hermit
Thrushes. I get some April reports of SINGING Swainson's Thrushes, and I can
be quite certain that these are erroneous. Despite the fact that this is one
of the most distinctive of all bird songs, at least to me, some birders seem
to mistake other species for Swainson's Thrush. In my experience, and that
of nearly all other birders, Swainson's Thrushes (and other brown thrushes)
DO NOT sing on migration, and in fact not until about 10 days to 2 weeks
after they arrive on territory-- starting about May 20th or so. For the
most part, the first Swainson's Thrushes that are reported give a series of
soft "whit" calls, or hop out briefly onto a forest trail in silence. Most
of them are probably overlooked because of their silence.
Nevertheless, we do get a few credible late April (but never early April)
reports of Swainson's Thrush in some years. I, like you, am one of those
birders who pays great attention to migration arrival and departure dates,
and I have religiously compiled tables of such dates for Vancouver since the
late 1960s. For Swainson's Thrush, our mean arrival date over 32 years is
May 6th in Greater Vancouver. However, for 9 years, the arrival date was in
April: arrival dates vary from April 16th to May 20th. Some of the April
arrival date records are by long-experienced and reliable observers that I
have no reason to question. Nonetheless, April arrival dates in Vancouver
are unusual for Swainson's Thrush, involving only a tiny vanguard of the
population (Joel Geier makes a good point), and I will continue to question
nearly all April records of the species.
Despite all this-- two days ago, on April 25th, I was birding along Shaw
Road, a forested road just south of Lake Samish in Skagit County, in
northwestern Washington. There were quite a few spring migrants about,
including 2 Hermit Thrushes. One of the birds I recorded was a Swainson's
Thrush, which gave a series of about 15 "whit" calls in the forest uphill
from Shaw Road. No, I did not see the bird-- searching through the dense
forest undergrowth would have been a futile effort-- but this is a call I
learned to identify more than 50 years ago, and I am as certain of this
identification as of any of the other birds I saw and heard that day.
Dave, you may have failed to find Swainson's Thrushes in April for 40 years
or more, but I predict that you will see or hear one, one of these years;
April Swainson's do occur occasionally, even in BC. It's easy to say "if I
haven't seem 'em in April, they don't occur in April", but "rarely" is not
the same as "never". To you and to anyone else who has to review
exceptionally early reports of Swainson's Thrush, my advice is: be
critical, question these reports and request photos or other evidence, but
be willing to admit that a few of these reports are valid. And birders, if
you do report Swainson's in April, be prepared to be questioned and to
provide some details of your sighting!!
Wayne C. Weber
Delta, BC
contopus@xxxxxxxxx
From: obol-bounce@xxxxxxxxxxxxx [mailto:obol-bounce@xxxxxxxxxxxxx] On Behalf
Of David Irons
Sent: April-25-14 12:34 AM
To: Brandon Green; OBOL Oregon Birders Online
Subject: [obol] Re: Spring Arrival Dates: Long and likely annoying for some
Brandon,
For more than a week now (since at least the 16th of April) there have been
almost daily reports of Swainson's Thrushes showing up on OBOL and in the
daily eBird rare bird alert for Oregon. I believe that every single one of
these reports is suspect. I looked at the eBird map that you provided for
all-time April reports of Swainson's Thrushes. It covers many years and has
several clusters of reports that are highly questionable. That said, there
are some from observers who none of us have any reason to doubt. These
reports, seem to be clustered (for the most part) over the last few days of
April (27th-30th). I consider any report in April to be early and any report
before about the 25th of April to be exceptionally so. We can argue over how
to define "exceptional," but that's really not the point.
We go through this exercise every Spring on OBOL. The fact of the matter is
this, not that many birders pay close attention to spring arrival dates and
if asked many could not tell you when Swainson's Thrushes, Yellow Warblers,
Warbling Vireos, or Willow Flycatchers normally arrive in the Willamette
Valley. Without an understanding of spring migration phenology, one is
unlikely to apply much rigor or objectivity to what they think they are
seeing because they have no reason to. If you believe what you are seeing is
normal, why would you question it? If on the 20th of April you see a bird
that looks like a Swainson's Thrush (the default w. OR thrush in the minds
of many Oregon birders) and you don't think or know that a 20 April
Swainson's Thrush is unusual, would you be skeptical about your own
observation?
If you look around the OBOL 'room,' the folks who view these early
Swainson's Thrush reports with skepticism are folks like Jeff Gilligan-Jeff
has been birding in Oregon for 50+ years; Tim Rodenkirk-Tim goes birding
almost every day, keeps a very detailed database on the comings and goings
of birds in Coos and Curry counties. Tim can authoritatively answer almost
any question about the abundance, distribution, and seasonality of birds in
these counties, I know because I regularly ask him such questions; Wayne
Hoffman-Wayne has been birding in Oregon for decades and has been a very
active birder since at least the 1970's); Mike Patterson-Mike has been
birding in Oregon since the early 1970's (at least). He has been the Oregon
CBC editor for North American Birds for about two decades and he has been
banding along the Oregon coast (Swainson's Thrush central) for 11 years.
These are birders who have been to this rodeo. We've all encountered out of
season reports of Swainson's Thrushes made by folks who were absolutely
certain of what they saw. Swainson's Thrush gets reported on an Oregon CBC
every year. Hermit Thrush is the only Catharus thrush that regularly winters
in Oregon, whereas Swainson's is a mega-rare bird here in winter. Swainson's
also get reported somewhat regularly in late March and the first 2-3 weeks
of April, when Hermit Thrushes are the default thrush in western Oregon.
Ever since I started birding seriously, I have paid particularly close
attention to migration/arrival/departure dates. Back in the mid-1980's David
Fix, Steve Heinl, and I shared an apartment at the base of Skinner's Butte
in Eugene (3rd and Pearl). During spring migration, we birded the Butte
every single day, often making more than one trip up the hill per day. At
the beginning of every season, we would make our predictions for the exact
day each neotropical species would first appear on the Butte. We were rarely
off by more than a couple of days. As the years passed and our sphere of
"young guard" birding buddies grew to include Matt Hunter, Dennis Rogers,
Rob Fergus, David Bailey and Jim Johnson, this game only intensified. We all
started each spring migration on a mission to find as many "first of the
season" birds as we could. If there were mid-April Swainson's Thrushes to be
found, I dare say one of us would have found them. I'm pretty certain that
I've never seen a Swainson's Thrush earlier than 3 May (and I was surprised
by that one). Since those early days, I've done a couple of stints writing
field notes for Oregon Birds and I've been Oregon's Regional Editor for
North American Birds since 2003. In order to write these columns, one has to
be intimately familiar with migration phenologies.
There are two additional phenomena that are somewhat universal in the
birding world. One might be described as "me tooism." The other is the
tendency to embrace oversimplified one-size-fits-all explanations when it
comes to explaining early or late reports.
Me Tooism -- Once a bird is reported by a seemingly trustworthy observer, it
is as though a permission slip has been issued to the rest of the birding
community. If an early report of say a Swainson's Thrush or Willow
Flycatcher is posted on OBOL, you can almost predict a number of "me too"
reports in subsequent days. "If birder X is reporting one, they must be
around."
Oversimplified Explanations -- This season's example is the combination of
drought in California and the stretch of unseasonal warm and sunny weather
that we enjoyed during the first two weeks of April. At some point there was
some chatter on OBOL about birds arriving early in California and that the
drought and nice early April could explain some surprisingly early reports
in Oregon. Again, another permission slip was issued. A smattering of early
arrivals occur every spring migration. What we've seen this year can hardly
be considered an anomaly. Also, the generally poor understanding of
phenology among rank and file birders leads to birds being reported as
"early" or "late" even when they aren't. There were questions about the
first Hammond's and Dusky Flycatchers on Skinner Butte. These two species
show up every year by the 15th of April, often a few days earlier. This
spring there have been a few species that have shown up 2-5 days earlier
than the normal FOS reports. However, aside from the flurry of Swainson's
Thrush reports and the likely incorrect report of a Willow Flycatcher from
Detroit Lake, I can't think of any reports that I found to be shockingly
early.
The California drought and warm spell probably shouldn't be offered as a the
reason for multiple Swainson's Thrushes being reported between the 15th and
20th of April (at least two and more like three weeks early). If you look
into the points of origination, the migration routes, and the timing of
spring migration for the many neotropical species that pass through Oregon
in the Spring, you'll realize that a single factor like the California
drought, or the period of nice weather we had in April is unlikely to have
had a wholesale effect on the entire suite of neotropical migrants. Some
birds start in the desert southwest, some start in Mexico and Central
America, and others come from as far away as South America. The routes taken
to reach Oregon do not follow a single pipeline running straight up through
California.
Approximately three full months pass from the date when the first Rufous
Hummingbird (the earliest neotropical migrant) reaches the southern Oregon
Coast, to the date when the first Common Nighthawk (the latest neotropical
migrant) arrives in the Siskiyou Mtns. and the southern reaches of Oregon's
Coast Range. When they left their wintering grounds, these birds could not
have known that they would encounter drought conditions in central
California, or that a 10-14 day stretch of really nice weather would occur
in Oregon during early April. In reality, these comparatively local
climate/weather anomalies probably didn't alter the path or the timing of
the migrations for most species. Perhaps the early wave of Western Kingbirds
that we had might be attributed to birds finding no food in California's
drought-stricken Central Valley and continuing to push north, but it's hard
to know. Most of the other species that typically show up in the first half
of April (Hammond's Flycatcher, Pacific-slope Flycatcher, Cassin's Vireo,
Nashville Warbler and Black-throated Gray Warbler) appeared on schedule. In
recent days, there have been ever so slightly early Black-headed Grosbeaks
and a Yellow Warbler, but true outliers have been no more numerous than a
'normal' spring based on the reports that I've seen.
I'm sure that I appear more skeptical than most about out of season reports.
This skepticism doesn't come from being a cranky, distrustful old guy who
has nothing better to do with his time than cast doubt on the reports of
other birders. My skepticism comes from 40+ years of seeing the same ID
mistakes repeated year after year. I endorse the use of eBird and I think
it is a wonderful tool. I have a similar opinion of OBOL, as it among the
most lively and educational statewide birding forums in North America.
Despite these endorsements, I do not accept (at face value) everything that
I see reported through via these forums.
If you think you are seeing a Swainson's Thrush in Oregon during April, I
encourage you to take and post photos. It may seem silly to document a
species that will be dirt common throughout much of Oregon a month from now,
but if we are to stretch the bounds of current knowledge, rigor,
objectivity, and proof need to be part of the process.
Dave Irons
Portland, OR
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