Tuesday, 29 October 2013

Darwin's Finches. Experiences in the Galapagos Islands

While the search goes on for the genes involved in the evolutionary divergence of Darwin’s finches*, together with the molecular mechanisms involved in morphogenesis of the beak and how those mechanisms are controlled, the Galapagos are visited by those keen to see these finches and how they live. But even experienced birdwatchers can have difficulty in identifying what they are seeing. Some species are easy to recognise, the Warbler Finch, for example. But for the Ground finches in particular identification can be puzzling. Colour is of no help. The beak is the key feature together with body size. When you think you have it worked out on one island, the move to a new island the next day can leave one bewildered. That is because a large member of a small species on island A can be very similar to a small individual of a larger species on island B. We found the Small and Medium Ground Finches on Santa Cruz could produce very puzzled observers. Peter and Rosemary Grant explain why: …medium ground finches on Santa Cruz are larger on average and vary much more than elsewhere. The beak is the key distinguishing feature but the variation within a single species can be so great that there can be overlap with another species. It is not impossible that you may be looking at a hybrid. Hybridisation is said to be rare but the offspring are fertile.

During our trip to the Galapagos we saw 10 of the 13 recognised species (ignoring the split of the Warbler Finch). The only real site for the really rare Mangrove Finch is closed to visitors (although the odd party has been lucky with a sighting elsewhere). We did not go high enough on Floreana for a Medium Tree Finch, the only island on which it occurs. We did go to places where we might have seen Large Tree Finches but on the days with the best chances and good access the weather closed in.

Sighting is one thing, video photography is another. I managed to get some footage of six species, especially those that seem to have no fear. This footage is shown here but is better seen by pressing the view in YouTube option:

I see that very recently published field guides are getting better reviews than their predecessors, especially when it comes to how they deal with Darwin’s finches. The books available up to a short time ago were really not very good. The human guides are excellent but they are not close to hand all the time to witness the fleeting appearance of a bird.

What I had not realised until we got there is just how tough and subject to changes in weather and climate some of the island environments are. Variations in rainfall, for example, affect the plants and invertebrates that provide the food for the finches. Droughts produce population crashes as well as marked selection for beak size with the outcome depending on which other species are present on a particular island competing for seed of the same size. This appreciation of the ecological factors in the evolution of Darwin’s finches is why I now suggest that visitors to the Galapagos should read the Grants’ book that summarises their research before going rather than after, like I did.

Equally as fascinating as Darwin’s finches are the human visitors to the Galapagos. Despite all the vessels having excellent naturalist guides on board the level of ignorance is astonishing. The problem seems to be that the Galapagos is sold as a destination for adventure holidays, particularly by travel agents in the USA, and hordes pour onto the popular islands seemingly immune to the acquisition of knowledge or interest in the natural world.

People watching is, therefore, in small doses also an educational experience not to be missed. Some of the conversations would form great lines for a sitcom. How can anybody in the western world escape knowing the existence of Darwin’s finches and why they are important? Even creationists have heard of Darwin’s finches. Well, there are lots of visitors to the Galapagos who have escaped knowing.

† I cannot recommend the Grants' book more strongly. It is clear they succeeded in achieving the goal they set out in the preface: Our goal, like [David] Lack's, was to capture the essentials and the highlights for an intended audience of students. Grant, P.R. & Grant, B.R. 2008. How and Why Species Multiply. The Radiation of Darwin's Finches. Princeton and Oxford: Princeton University Press.