Gould has divided into four sub-groups.
All these species are peculiar to this archipelago; and so is the
whole group, with the exception of one species of the sub-group
Cactornis, lately brought from Bow Island, in the Low Archipelago.
Of Cactornis the two species may be often seen climbing about the
flowers of the great cactus-trees; but all the other species of
this group of finches, mingled together in flocks, feed on the dry
and sterile ground of the lower districts. The males of all, or
certainly of the greater number, are jet black; and the females
(with perhaps one or two exceptions) are brown.
(PLATE 81. FINCHES FROM GALAPAGOS ARCHIPELAGO. 1. Geospiza
magnirostris. 2. Geospiza fortis. 3. Geospiza parvula. 4. Certhidea
olivasea.)
The most curious fact is the perfect gradation in the size of the
beaks in the different species of 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 (Plate 81) Figure 1, and the smallest in Figure 3; but
instead of there being only one intermediate species, with a beak
of the size shown in Figure 2, there are no less than six species
with insensibly graduated beaks.
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