Date: 10/29/20 9:04 am
From: Paul Sullivan <paultsullivan...>
Subject: [obol] Re: Catharus thrush phenology: eBird Target List data
Hi Wayne,

Thanks for this information; it sheds good light on the question at hand.

However, your explanation begs one question. Who knew there was something
called “Target” feature in eBird? And how would one ever find it? Could
you give a naďve, ordinary person directions to get to get to such a

Does one have to be signed up with eBird, have a large battery of eBird
checklists on file, and a “wish list” of birds in location X to use the
“Target” feature?

Asking for a friend.

Paul Sullivan

From: Wayne Weber [mailto:<contopus...>]
Sent: Wednesday, October 28, 2020 8:48 PM
To: OBOL2 <obol...>
Cc: PAUL SULLIVAN <paultsullivan...>
Subject: Catharus thrush phenology: eBird Target List data

Paul and Oregon Birders,

In late October, Hermit Thrush is far more likely in your area than
Swainson’s. Swainson’s is still possible, but highly unlikely at the late
date of October 28.

To quantify the likelihood of each species in October, I used the “Target”
feature of eBird for nearby counties, which lists the percentage of lists
containing each species for the whole month. Yamhill has a very small sample
size for October (327 lists), so is not very useful. However, Multnomah has
8133 October lists, Washington has 5211, and Clackamas has 2137. Here are
the results, in percentage of October checklists containing each species:


Hermit Thrush 6.15%

Swainson’s Thrush 0.87%


Hermit Thrush 1.34%

Swainson’s Thrush 0.69%


Hermit Thrush 3.37%

Swainson’s Thrush 0.47%

As you can see, Hermit Thrush is far more frequent than Swainson’s. I am
surprised at the apparent scarcity of Hermit Thrushes in Washington County;
the data for Multnomah and Clackamas are closer to what I would expect.

Of course, these data are for the entire month of October. Most of the
Swainson’s sightings were probably in the first week of October. In the last
week, I would expect that Hermit is 10 to 20 times as likely as Swainson’s.
However, as you know, Hermit Thrushes do spend the winter in your area in
small numbers.

In my area (Vancouver, BC), the peak fall migration for Hermit Thrushes is
about mid-September to mid-October. I would expect that that they are not
much later (maybe a week?) in northwestern Oregon. Thus, a date of October
28 is getting kind of late even for Hermit Thrush, unless your bird was
preparing to spend the winter.

I hope these data illustrate how useful “Target Lists” can be to quantify
the likelihood of occurrence of any species in a particular month, at least
for counties with large sample sizes. (The same could be done for an entire
state, but this would be much less useful for a state as large as varied as

All the best,

Wayne Weber

Delta, BC, Canada

<contopus...> <mailto:<contopus...>

From: <obol-bounce...> <mailto:<obol-bounce...>
[mailto:<obol-bounce...>] On Behalf Of Paul Sullivan
Sent: Wednesday, October 28, 2020 9:44 AM
To: <obol...> <mailto:<obol...> ; YamhillBirds
Subject: [obol] Catharus thrush phenology

It’s foggy here in McMinnville this morning. Just moments ago at 9 AM, I
was scanning my backyard, counting the increasing number of juncos (up to 12
now), when a brown bird emerged from under a bush. I thought, “Oh good, a
fox sparrow.”

Then I realized, “No, it’s a THRUSH!” I locked on it with my binoculars as
it hopped straight toward me, showing the thrush, not sparrow beak. Was it
hermit or Swainson’s? My first thought was Swainson’s, but then I thought
could it be hermit? I was waiting for it to turn and show me its tail, when
it suddenly exploded sideways out of my field of view and was gone. I
haven’t seen it again.

I checked my copy of The Birds of Rummel Street that tallies 23 years of
sightings in this backyard (1993-2016). The data displays presence or
absence of a given species in each of 4 weeks in each month of each year.

Swainson’s thrushes were recorded in 58 times, all between the first week of
April and the first week of October.

Hermit thrushes were recorded in 3 times between May and October, and 4
times between the third week of November and the second week of February.

What do folks who follow phenology say?

Paul Sullivan


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