Geospiza, from one as large as that of a hawfinch
to that of a chaffinch, and (if Mr. Gould is right in including
his sub-group, Certhidea, in the main group) even to
that of a warbler. The largest beak in the genus Geospiza
is shown in Fig. 1, and the smallest in Fig. 3; but instead of
there being only one intermediate species, with a beak of
the size shown in Fig. 2, there are no less than six species
with insensibly graduated beaks. The beak of the sub-group
Certhidea, is shown in Fig. 4. The beak of Cactornis is
[picture]
1. Geospiza magnirostris. 2. Geospiza fortis.
3. Geospiza parvula. 4. Certhidea olivasea.
somewhat like that of a starling, and that of the fourth
sub-group, Camarhynchus, is slightly parrot-shaped. Seeing this
gradation and diversity of structure in one small, intimately
related group of birds, one might really fancy that from an
original paucity of birds in this archipelago, one species had
been taken and modified for different ends. In a like manner
it might be fancied that a bird originally a buzzard, had been
induced here to undertake the office of the carrion-feeding
Polybori of the American continent.
Of waders and water-birds I was able to get only eleven
kinds, and of these only three (including a rail confined to
the damp summits of the islands) are new species.
