Darwin's Finches
If the giant tortoise is the symbol of the Galapagos
Islands, then Darwin's finches must be the symbol of evolution
in the Galapagos. It may seem curious that of all the animals
in the Galapagos,this group of very drab and dull birds is most
closely associated with Darwin's name. He was neither the first
to see them (they are mentioned in passing by Captain James
Colnett in 1798) nor did they figure much in his writings subsequent
to the "Voyage of the Beagle". Despite the fact that
they intrigued Darwin, they are far too complex a group of animals
for Darwin to have understood. Nevertheless, they played an
important role in helping him recognize the reality of the evolutionary
process. The name was first applied in 1936, and popularized
in 1947 by the ornithologist David Lack, who published the first
modern ecological and evolutionary study of the finches. Today
Darwin's finches are the subject of intense study, and they
are revealing much about the evolutionary process.
Darwin's finches share similar size, coloration,
and habits. Their salient difference is in the size and shape
of their beak. However, beak shapes can be very variable, and
the size and shape in one individual can overlap into the range
of another species. Michael
Harris, the author of a Galapagos bird guide-book
cautioned: "It is only a very wise man or a fool who thinks
that he is able to identify all the finches which he sees."
With finches, it is often an issue of "shoot first and
ask questions later." Indeed, I only realized that I saw
some finches well after my trip, when poring over the photographs.
There are presently 14 species of birds recognized as Darwin's
finches - 13 in the Galapagos, and one on Cocos Island.
On one of my early trips to the Galapagos, one
of my students wondered why we need to worry about naming them;
why can't we just enjoy them for what they are? There is power
in a name; to know the name is to understand the named. This
is especially so in that branch of biology known as taxonomy
or systematics. The taxonomist not only applies a name to an
organism, but, by ranking those organisms into hierarchies of
names, attempts to portray evolutionary relationships. Since
1758, taxonomists have used the system of Linnaeus to organize
the living world. Linnaeus gave each organism a binomial: genus
and species, which are ranked in higher and higher groupings:
Kingdom
|
a group of related phyla
|
Phylum
|
a group of
related classes |
Class
|
a group of
related families |
Order
|
a group of
related genera |
Genus*
|
a group of
related species |
species**
|
an individual type of organism
*Genus and species names are always italicised
**species names are always lower case
|
It should be clear from this table that the only
"real" entity is the species. The higher groupings
are merely an assessment of how species are thought to be related
to other species, and different taxonomists may very well disagree.
Among the Darwin's finches, there is general agreement as to
the existence of 13 Galapagos species, although there may be
one or two more or one or two less, depending on how one assesses
several unusual populations. There is disagreement, however,
about how those 13 species are organized into genera. Traditionally,
the finches are divided into four groups, each representing
a single genus: the ground finches
(Geospiza), the tree finches (Camarhynchus), the
warbler finch (Certhidea) and the Cocos finch (Pinaroloxias).
As a group, the tree finches are more heterogeneous than the
ground finches and it is current practice to subdivide the tree
finches into three genera: Camarhynchus (the tree finches),
Platyspiza (the vegetarian finch) and Cactospiza (the
woodpecker and mangrove finches). On the other hand, finch expert
David Steadman feels that splitting the finches into six genera
emphasizes their differences and suggests that all of the finches
should be united as 14 species in the singe genus Geospiza
to emphasize their similarities!! But whether you split them
into six genera or lump them into one, everybody pretty much
agrees on the same 14 species. The only real entity is the species.
The table below gives the genus and species names for all of
the finches:
|
THE FOURTEEN SPECIES OF DARWIN'S FINCHES
|
|
Common Name
|
Genus
|
species
|
Ground Finches
|
|
|
Small Ground Finch
|
Geospiza
|
fuliginosa
|
Medium Ground Finch
|
"
|
fortis
|
Large Ground Finch
|
"
|
magnirostris
|
Sharp-beaked ground Finch
|
"
|
difficilis
|
Cactus Ground Finch
|
"
|
scandens
|
Large Cactus Ground Finch
|
"
|
conirostris
|
Tree Finches
|
|
|
Small Tree Finch
|
Camarhynchus
|
parvulus
|
Medium Tree Finch
|
"
|
pauper
|
Large Tree Finch
|
"
|
psittacula
|
Woodpecker Finch
|
Cactospiza
|
pallidus
|
Mangrove Finch
|
"
|
heliobates
|
Vegetarian Finch
|
Platyspiza
|
crassirostris
|
Warbler Finch
|
Certhidea
|
olivacea
|
Cocos Island Finch
|
Pinaroloxias
|
inornata
|
|
