To whom doth the black bird sing? (Part 2)

(continued from last weeks post)…These finches get this protein indirectly by drinking the blood of seabirds which have consumed the fish: a superb and daring adaptation for a small passerine bird and one which has provided its common name: the Vampire Finch. (To see a clip of a Vampire Finch in action, click here.)

In 2012 I was permitted to visit Wolf Island and, sitting down amongst the white plumaged Nazca Boobies, contemplated the time scales that permitted the arrival and establishment of these small terrestrial finches which most likely would not have survived without the adaptive trick of feeding on “life’s blood”.

I was as much astonished to find in a small opening amongst the low croton bushes (Croton scouleri var. darwinii) a magnificent gramivorous Large-billed Ground Finch (Geospiza magnirostris) singing his heart out. I immediately asked myself “…to whom doth he sing?”.

On returning to Santa Cruz Island I paid a visit to the library of the Charles Darwin Research Station to revise notes left by the small list of people who have visited the island. There was not much to be found but a little later Peter Grant, the world expert on Darwin’s Finches, described to me how he had found six G.magnirostris in the same area in 1978.  These, after 35 years, could not have been the same birds, for I believe the record for longevity of finches is 14 years.  Apart from the singing male I saw four others, two of which were females.  Thus singing for this male was not just “blowing in the wind” but the vital road to sustaining this species on the island. So this tiny population continues, defying extirpation and the potentially lethal effects of the infinitely small gene pool of the population.  Are these birds the result of the unique arrival of a pair or are they the remnants of a larger population that now hangs by a thread? Will the population grow? I observed the birds feeding on the seeds of the straggling cactus Opuntia helleri, endemic to the northern islands.  This is fortunate for the cactus is locally abundant but like all other plant species, dependant on the annual rainfall, which is capricious. Peter Grant observed that they had eaten the fruits of the Croton bushes, the dominant plant of the island. Thus the saga of arrival and establishment continues after 2.5 million years.

The island is pristine, unaltered by human hand. This is a status merited with extreme rarity in the world of islands or in the world at large. What we witness is the interplay of life forms and the environment that, in the case of the Darwin’s finches, has been played out repeatedly since the first successful arrival 2.5 million years ago, in spite of the closure of the Central American Seaway and the continued series of glaciations of the Quaternary Ice Age.  We are privileged to observe how nature works in its most pure form and to see the results of the theory of Natural Selection produced before our very eyes and to wonder at the process.

Written by Godfrey Merlen

The Finches of Galapagos need your help. If you would like to learn more about these incredible birds, the threats to the songbirds of the archipelago, and what we are doing to help conserve them, please visit http://www.darwinssongbirds.com/.

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