Land Birds


 


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

Identificaion of finches can be extremely intimidating. Indeed, for several years I filed away my photographs wihout really looking at them until I could work up the courage to try. I had many discussions with guides, and one year, I even brought my pictures with me. Now, I feel relatively confident in my identifications (but remember: "It is only a very wise man or a fool who thinks that he is able to identify all the finches which he sees."). Below are images of the 11 Darwin's finches that I have seen.

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    for more info, contact Dr. Robert Rothman: rhrsbi@rit.edu