[birding] More on the Henslow's Sparrow at EEWilson, 15 Jan

[Douglas Robinson]

Hi folks,

I was out of town the last few days and responded to only a couple emails
about the Henslow's Sparrow. Given the interesting range of responses, I
thought I would summarize more about the sighting.

First, here are the fieldmarks I saw from a distance of about 8 feet: chunky
bodied sparrow with an olive nape, tertials with a broad rufous distal
margin, and a scaly-appearing back. The back feathers were very round-tipped
(not elongated) and black with dark chestnut toward the distal edges. Each
feather was edged with a very narrow (about 1 mm) and uniform-width white
fringe. It's the fringes on dark feathers that made the back appear "scaly."

As I reported earlier, when I flushed the bird first by nearly stepping on
it, it flew about 4 feet and dived into a patch of grass. The bunch of grass
it was under had a gap in the canopy and I could see the bird move into an
open space. I moved slightly and focused my binoculars on the bird. I could
see the nape, back, and upper edge of the right wing (tertials) very
clearly. The rest of the bird was mostly obscured by grass. I watched it
there for several seconds and it was not moving. So I tried to shift to the
side carefully so I could see the head better. As I did, the bird ran out of
sight. I then took a couple steps forward to where it had been sitting and
it flew into a briar patch.

I watched carefully as it flew. When the bird flew, it did so with a
"herky-jerky" movement; low flight that is somewhat indirect in that it
seemed like the bird was being pulled forward by the side of its head,
rather than going straight ahead.  I quickly walked up to the briars and
tried for 2 or 3 minutes to re-locate it. I had no success, but knew I had
seen enough to make a conclusive identification (see below), and I decided
that if other people were going to see it, I had better not harass it any
more. (Yeah, imagine that; walking away from a Henslow's Sparrow in Oregon
because you want others to have a chance at it. I did the same thing with
the Sedge Wren last year in this same field. When I flushed the Sedge Wren
as I was walking slowly through the field I hardly broke stride and kept
right on walking. My first thought was: "Ah ha, a Sedge Wren. Other people
will want to see that, so I'll leave it alone for now.")

So, why is seeing the nape, back, and tertials enough for a conclusive
identification? If you know Ammodramus sparrows, you know that is enough.
First and foremost, no other species has a nape the same color. Henslow's
has that dark olive-green color, which is like no other species. Second,
combine that with a rufous wing patch caused by the colored patch in the
tertials and the scaly-appearing back pattern and you have eliminated all
the other possibilities.

For example, LeConte's, Sharp-tailed, and Grasshopper sparrows have grayish
napes (all with somewhat different patterns of streaking on them and
Grasshoppers have more of a buffy-gray nape); Baird's has a paler, rather
buffy nape. None of the other common local sparrows like Savannah, Swamp,
Lincoln's or Song Sparrows have an olive nape.

All the other species have back patterns that look streaky, which is largely
caused by back feather shape and the occurrence of broader color patterns
toward the margins of the back feathers. Henslow's is different in that, in
fresher plumages as they would be in during fall and early winter, those
fringes are narrow and give the whole back a scaly appearance.

Last, the broad rufous tertial margins are not present in LeConte's (very
buffy instead), Sharp-tailed (darker brown with narrow paler edge),
Grasshopper (patterned brown and buff), Baird's (very buffy edges),
Lincoln's (buffy to tan edges), nor Savannah (pale buffy fringe).  Song and
Swamp have some rusty-brown wing feathers, but typically the pattern is
different; in Swamp the rusty is brighter toward the inner instead of outer
edge and in Song the red-brown is dull and does not contrast that much with
the rest of the wing. Note, too, that both Marsh and Sedge Wrens have
streaky backs. I won't go into all the other reasons Henslow's Sparrows are
not wrens.

So, if you get a clear look at nape, back, and tertials, you can eliminate
the other possible identifications.

It's too bad the folks who tried later the afternoon I found the Henslow's
Sparrow and the next day did not get a clear look, but they all know now how
hard it is to relocate a Henslow's Sparrow during winter. They are
incredibly elusive. They prefer to run on the ground whenever possible. When
pressed, they hide in underground tunnels such as tortoise burrows (the
Southeast USA) and vole holes.

So, to finish a long email, let me summarize my experience with this and
similar species. First, this is not the first Henslow's Sparrow I have seen.
I have studied the species on its wintering grounds in Alabama and Florida.
The previous posting had a link to a pdf of a paper I wrote with my graduate
student on winter habitat use of Henslow's Sparrows. I have seen dozens of
these guys during winter. That is another reason I did not continue to chase
the EE Wilson bird for better looks. I know the bird's flight behavior, I
know the key field marks that make a short or obscured look a conclusive
identification, and I know how tough they are to see well.  I have also seen
the species regularly in Illinois during spring and summer (check my book
Southern Illinois Birds, 1996, for a nice photo of a Henslow's Sparrow).

Last, I have seen hundreds to thousands of all the aforementioned species
except Baird's. I've gotten one look at Baird's ever, excepting studies of
specimens in museums.  LeConte's are regular in winter in southern Illinois
and I have seen hundreds of them over the years; yes, hundreds.

Enough of a long email. I hope someone else can get the bird to cooperate
long enough to get good looks.  Would be great to move this Henslow's
Sparrow out of the single-observer record category and into a multi-observer
Oregon record.

Have fun out there, and try stomping through some fields this winter; you
never know what you might kick up.

Douglas Robinson


-- 
W. Douglas Robinson
Dept of Fisheries and Wildlife
104 Nash Hall
And Oak Creek Lab of Biology
Oregon State University
Corvallis, OR 97331

http://fw.oregonstate.edu/robinson

541-737-9501