Out walking the Fill in mid-afternoon around 3pm after wondering were
all the passarines were (the breeze was up but the sun was still
peaking through the high clouds).

I noticed a pair of bird flying tail astern. Falcon shaped. Medium
sized (bigger than a crow?).

In the bins they were clearly interacting each trying to get the high
side of the other and dropping talons inducing the lower bird to
roll. After a couple of interactions like this they split one heading
back up to the UW and area to the west of it by circling and climbing
under power (with the occasional soar but there wasn't much
convection today). The other I lost track of. He stayed in view (in
the bins but at rather great distance) for between 5 and 10 minutes.

Unfortunately that initial encounter of the pair was a close as they
came to me when I was thinking more about behavior than field marks.
But even when circling I got a good view of the underside and the
upper side.

I was a little puzzled. They were both the same size and colored the
same: light gray or light bluish gray above and whitish underneath.
Both clearly with falcon wings and flight style (no flap, flap, flap,
glide). So it's a falcon.

As the bird climbed I could see the "head" (i.e. the underside and
side of the throat and face) looked clearly white and the underside
of the body a bit darker but not quite grey. The upper side of the
body and wings was uniform light bluish gray (certainly not dark gray
or dark blue). The tail didn't have any clearly obvious barred patterns.

I'm not great at falcon id (not seen enough of them to know the
details first hand) but this had me a bit puzzled. I didn't see any
red or brown on the upper surface or strong tail barring plus the
size seemed wrong (not delicate) ruling out a American Kestrel. Again
no dark blue upper surface and no tail barring ruling out a Merlin.
No dark axiliaries so not Prairie Falcon (and it's out of
range ... :-) ).

So that leaves a Peregrine or Gyrfalcon. So two Gyrfalcon over
Seattle would be a bit too incredible. Plus in the photos and
drawings I've seen of Gyrfalcon they seem more bulky than this.

So I get to a Peregrine. but shouldn't it be darker above?

In "Hawks in Flight" I see they mention the subspecies tundrius as
"Adults are light grey above. Some individuals show a blue-gray cast
on the back and tail. The paler tones, coupled with a more restricted
facial pattern, mute the bold helemeted appearance of the anatum".

This is a very close match to what I saw (including the white "head").

So I believe I saw a pair of Falco perigrinus tundrius over the Fill.

Comments welcome.
--
Kevin Purcell
kevinpurcell at pobox.com