Hi Dave et al.,
I was down in the same area Dave and Shawneen were at the same time last
year and have spent quite a few early springs down there visiting family.
This year and last March I also spent time down at the Salton Sea.
Anyhow, I have often pondered the same questions Dave mentioned.
I like the leap frog theory on these early Yellow Warblers. It makes sense
that this early wave may be a subspecies that nest in desert riparian
corridors. I saw no Yellows over around the Salton Sea or in Yuma where I
birded the past week (there was a wintering bird in Brawley at Cattle Call
park though). A second wave arriving a bit later would sure make sense.
Also, without checking, I imagine that for some shared migrants we would be
talking about a range of different subspecies which may have evolved
different migration movements and timing.
That said I wonder how many of these species we share that migrate through
SE AZ even end up in Oregon? It may be that many of the neotrops that nest
in OR arrive via California or routes further west or arrive from a mix of
different migratory corridors with different average arrival times? MOTUS
may be more helpful answering some of these questions than eBird.
Over this past week or so on the south end of the Salton Sea I spent three
mornings at Yuma West Wetlands which I highly recommend. It is an old dump
along the Colorado River that has been turned into a spectacular park with
a wonderful riparian corridor and trail. There is also a Yuma East Wetlands
(good for Western Diamondbacks which I saw on both trips there). No Yellow
Warblers which I would have expected and no reports I noticed (except for a
wintering bird in Cattle Call Park in Brawley). I did have Warbling Vireo
in Yuma though and saw other reports. I noticed one local birder had
Pac-slope Flys in already but he was birding riparian corridors up in the
mountains (it looked like). So probably some difference in migratory
patterns even from SE to SW AZ.
Makes me wonder from which migratory corridor(s) our Western Oregon
breeders arrive from? Many of the Westside birds arrive early, mid-April to
the first of May and I think it is safe to say that the main wave of the
same species hits the Eastside later (think Memorial Day weekend at
Malheur). Then there are species like Black-throated Gray Warbler that seem
to occupy different habitats and may come from different wintering
populations. You have the Westside birds that like mixed deciduous/conifer
forests and riparian forests and then the Eastside birds that breed in the
juniper country! What are the odds they have a different migration
strategy? It is a tangled web for sure.
Not sure a lot of this can be untangled easily but it is pretty fun to
think about and super awesome to be able to go south and pick up on the
earlier migration in the desert areas of CA and AZ.
Oh, this is peak migration time for Rufous Hummers on the south coast of
OR- I saw one report on eBird from a few days ago (the 20th) of 15 Rufous
at Bullards Beach SP in Bandon and the observer said they were all over the
park! We just put up a fourth feeder, could get busy with this cold weather
coming this weekend?
Enjoy the early Oregon migration!
Tim Rodenkirk
Coos Bay
On Wed, Mar 22, 2023 at 5:41 PM David Irons <LLSDIRONS@xxxxxxx> wrote:
Greetings all,
As promised in a post I made last night, being in Arizona offered a
preview or sorts of the impending arrival of neotropical migrants in
western Oregon. I'll start by pointing out that my experience with Oregon's
spring migration phenology is heavily biased towards western Oregon because
I have never lived east of the Cascades, and I have rarely visited the
eastern two-thirds of the state before the last week of May.
Veteran birders across the state can often tell you almost down to the day
and certainly down to the week when the first sightings of various
neotropical migrants can be expected in their local area. One thing many of
us have been curious about is how fast these species come north. Is the
northbound migration of songbirds somewhat incremental or are these birds
moving quickly up the west coast from the south and arriving here within a
few days of when the first arrivals hit areas far to our south? Based on my
combined experiences of living for many years in Eugene and in the Portland
area, I have generally been inclined to think that most neotropical
migrants are moving somewhat incrementally, in large measure because of the
3-4 day lag (if not longer with some species) between the Eugene and
Portland area arrival dates of many species. Given some of my assumptions,
I expected to see more neotropical migrants arriving last week in Arizona
than we did.
During our trip we did most of our birding in Santa Cruz County, Arizona,
so I pulled up the eBird bar charts for that county to see when the initial
spike of reports occurs for many of our shared neotropical migrants. I was
particularly interested in those species that don't routinely winter in
Arizona and those species that arrive in western Oregon between about the
15 April and 10 May, which is when the bulk of our neotropical migrants
appear. I also looked at some of the earlier-arriving birds like Nashville
Warbler and Pacific-slope Flycatcher. What I found is that there is roughly
a two to three-week differential between the first waves of each species
reaching SE Arizona and the first waves of that same species arriving in
Oregon and this seemed pretty consistent across the board. Of course, there
are all sorts of variables that make perfect apples to apples comparisons
difficult, if not impossible, despite what appears to be a somewhat
consistent spacing of arrival dates across many species. For example, can
we assume that a substantial percentage of the populations of these
neotropical birds migrating into Arizona are continuing on towards Oregon?
How much of a factor is so-called 'leapfrog' migration? This is where the
earliest-arriving birds are more southerly breeders that stop well short of
Oregon and then are leapfrogged by those populations that nest in Oregon
and farther north. This would involve a second wave of later migrants
passing through Arizona and other points south that may be difficult to
detect if that species is common breeder to the south.
We are within about 20 days of the first migrant Nashville Warblers and
Pacific-slope Flycatchers being reported in western Oregon, thus I expected
to seem some of both in Arizona. I was surprised that we saw neither of
these species during our trip despite spending considerable time birding in
a variety of woodland habitats where other migrants were encountered.
Looking at the bar charts for Santa Cruz County, it appears that
Pacific-slope Flycatcher reports start to build during the third week of
March (last week) and Nashville Warblers spike during the fourth week of
March (now). It has been a delayed spring in southern Arizona, with snow
cover in many places just a couple of weeks ago. Pacific-slope Flycatcher
is definitely a leapfrog migrant in western Oregon and it may be that the
first birds that arrive in Oregon are coming on heading that does not pass
through Arizona. The first birds normally start arriving in western Oregon
around 12-15 April, and by late April breeding habitats in the Coast and
Cascade Ranges and the foothills of western Oregon valleys are well
populated with territorial singers. Then in early May there is usually a
small but noticeable second wave of Pac-slopes that can often be heard
giving their high-pitched "tink" call (not singing) as they move through
the westside lowlands, usually in habitats where they don't breed. These
are presumed to be birds that will summer and nest far to the north of us,
where the leaf out and early insect hatches occur much later in Spring. We
also saw no Warbling Vireos, MacGillivray's Warblers, Western Tanagers, or
Black-throated Grosbeaks, all of which typically arrive in western Oregon
between about16 and 25 April. Most of these species start appearing in
numbers in Santa Cruz County plus or minus the first week of April, again
roughly 2-3 weeks earlier than they arrive here.
As noted in the subject line, there was one conspicuous outlier that did
not align with the timing differential that seems to show up with
essentially all of the other neotropical migrants...and that was Yellow
Warbler. In western Oregon, Yellow Warbler is the latest arriving spring
warbler, rarely showing up before the last day or two of April and
generally not being conspicuous in western Oregon until after the first of
May. And yet, during our trip to Arizona we saw several Yellows, all males
(many singing) in lowland riparian corridors where they were presumably
establishing breeding territories. Looking at the Santa Cruz bar chart it
is apparent that Yellow Warblers don't routinely winter in the county and
in fact appear to be quite rare there from December-February. According to
the bar charts, early arrivers show up during the first week of March and
then build to peak numbers locally by the third week of March, fully 6-8
weeks earlier than they arrive in Oregon. There are all sorts of unanswered
questions that can be raised. Where do these early-arriving Arizona birds
winter? Is that wintering grounds a source for birds that summer much
farther north? If not, where are the more northerly breeders wintering and
does their migration route to Oregon and beyond pass through Arizona? Given
how early Yellow Warblers flood the southern Arizona riparian corridors,
how difficult is it to perceive the presence of birds that might still be
moving north through Arizona in April? I wish I knew the answers. With
advancements in tracking technologies, the ever-expanding network of Motus
tracking towers, and the continuing spring migration monitoring going on at
Bear Divide in California, many of these questions could eventually be
answered, and we may learn why Yellow Warbler migration timing in southern
Arizona looks so outwardly different than the patterns shown by other
neotropical migrants that summer in Oregon and migrate to and through
Arizona each spring.
Just some things to ponder as we patiently await the height of spring
migration.
Dave Irons
Beaverton, OR
