[Tweeters] Ageing Gyrfalcons

Bud Anderson falconresearch at gmail.com
Mon Jan 21 13:40:05 PST 2013


I have been asked several times over the last 10 days about ageing
Gyrfalcons, especially in reference to the bird being seen recently on Fir
Island in Skagit County. Of course, this is assuming that there is only one
Gyr on Fir Island right now. and I could certainly be wrong about that.

Marv Breece's excellent photo of this bird, posted on Tweeters today, is
especially instructive.

In my experience, most of the Gyrfalcons we get in western Washington are
brown immature or first year falcons. We rarely get black or white gyrs on
this side of the Cascade range. In all my years of looking, I have seen
only one black gyr on the Skagit (it was unbelievably gorgeous) and never a
white bird, although one was shot here in 1958 so they can occur locally
but very rarely. Maybe the guys up in Whatcom County can also address this
issue.

Juvenile gyrfalcons have a very unique brown color. It is unlike the color
on any other raptor. This odd color is seemingly di-chromatic, i.e. it can
appear to look brown or gray under differing light conditions. I have held
a juvenile brown gyr in hand and upon release and about 100 yards out, it
suddenly looked gray to us all. Very odd. So if you see a gyr and can't
decide if it is brown or gray, go with brown. The gray birds are just that,
clearly gray.

But it can be confusing, especially to beginning birders or those with
little Gyr experience.

However, in Marv's excellent photos of a juvenile brown Gyr, you can see
several much better features for ageing Gyrs. In one shot, you can clearly
see the blue cere and orbital rings that are so typical of a young falcon.
It is almost glacier blue, one of my favorite colors. You will also see the
vertical streaking on the front of this bird, much like a juvenile
peregrine or a Merlin. Finally, if you look at the brown back, there is
very little light feather edging on the scapulars and wing coverts, a
feature also diagnostic for age.

But we also have second year gyrs here, birds that return to the same
location to spend another winter which is known as philopatry. We have
established this to be true through our banding efforts. Second year gyrs
will differ significantly in appearance. These falcons will clearly be gray
on their back. They will usually have a whitish or pale yellow cere and
orbital rings (depending, apparently, on what they are eating).

But perhaps the best way to age them is to look at the wing coverts. Most
second year Gyrs will have several pale, faded, unmolted wing coverts that
are very obvious. Second year birds that I have seen seldom complete their
first molt. Have a look at the Gyr on the cover of Hal Oppermans book, A
Birders Guide to Washington, for an excellent example of this feature.You
can clearly see multiple faded first year feathers on the side of the birds
wing. This is typical for a second year Gyrfalcon in western Washington.
Use it to your advantage.

There are also third year or older, fully adult Gyrfalcons that show up
sometimes. These birds will be stark, often lighter, gray in the back,
cleanly molted in the wings, have a bright orange cere and orbital rings
with tiny narrow streaks in the bib, small spots in the lower abdomen and
sometimes barring in the flanks.

They will usually show extensive, lighter gray feather edging on the back
with a central horizontal light gray bar across each feather like the other
desert falcons (e.g. Prairie Falcons, Sakers, etc.).

Some of these older birds will be very light gray on their backs (almost
like an adult male harrier) in contrast to an almost pure white on the
front. These birds are often termed "silver Gyrs", not quite white but
verging on it.

In all age classes, look for the main field mark for a Gyrfalcon, the tips
of the primaries ending about halfway down the tail unlike a Peregrine or a
Prairie which end near the tip of the tail.

Hope this helps. Thanks to Marv and Hal for the photo references.

Bud Anderson
Falcon Research Group
Box 248
Bow, WA 98232
(360) 757-1911
falconresearch at gmail.com
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