A CGI P ITRE S . FALCON I DJi.
THE ICELAND FALCON.
Falco gyrfalco (in part)!.
T h e cliiel differences between the subject of the preceding
article and the Iceland Falcon have therein been succinctly
mentioned. I t remains to point out the characters which
distinguish the latter from the true Gyr-Falcon of the Scandinavian
Peninsula, and probably of countries further to the
eastward. In immature plumage the two birds greatly re-
Syst. Nat. i. p. 271 (1788). t Not Falco gyrfalco, Linnasus.
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F alco is l a n d u s , J . F . Gmelin*.
semble each other, so much so, that it is often not easy at
first sight to separate them, especially as the Icelander, like
the Greenland Falcon, is subject to a considerable amount of
variety in the prevailing shade of tint, and it is quite possible
that examples of the true Gyr-Falcon have occurred in these
islands, and have been mistaken for the commoner form.
As a rule, however, it may be asserted that in the Iceland
Falcon the crown of the head is lighter, and generally much
lighter, in colour than the back, while in the Gyr-Falcon the
crown of the head and the back are of the same hue, or the
former is darker. In the Gyr-Falcon, also, there is commonly
a very perceptible black mystacial streak or patch,
which in adults of this form is often as much developed as
we find it in the Common or Peregrine Falcon, and the
coloration generally is darker than in the Icelander. The
late Mr. Hoy, who was well versed in Falconry, and seems to
have been the first English writer to clearly distinguish the
two forms, has pointed out (Mag. Nat. Hist. vi. p. 108) some
other differences. The Icelander, he says, rather exceeds the
Gyr-Falcon of Norway in size; the tail is considerably
shorter; the wings are, in proportion, longer, and the head
is larger, so much so, that, in modelling the hoods for
trained birds of the two kinds, falconers use different blocks.
Whether all these distinctive features can be established on
the comparison of a large series of specimens, is perhaps
uncertain, but it does appear that in some parts at least of
the structure of the two forms there exists a remarkable
difference of proportion, which does not seem to have been
hitherto noticed. The average length of the sternum and
coracoid in Falco islandus, as ascertained by the careful
measurement of six female specimens, not specially selected
for the purpose, in the Museum of the University of Cambridge,
is 5-46861 in., wdiile the average length of the same
bones in as many specimens of F. gyrfalco of the same sex,
and in the same Museum, is 5‘0638S in. This would at
once show that the Icelander has the longer body of the two,
by nearly half an in c h ; but the difference becomes more
striking when it is found that the breadth of the sternal