Galapagos Ground-Finch ID?

[joemorlan]

I took these at the Darwin research station on Santa Cruz on 26 July 2008. Both photos are of the same bird.

The bird was by itself in a tortoise enclosure. Our local guide called it a Medium Ground-Finch, but when I asked him to look at it again (after it had flown into a tree) he agreed that it was a Large Ground-Finch. Since then one correspondent has said he thinks it was likely a Medium Ground-Finch.

All I can say is that its bill was bigger than any of the many Medium Ground-Finches I saw on this trip.

Please advise. Thank you.

[Brian S]

Joe

In my opinion this is a non-breeding/imm. male, and I would agree with the guide in its being a Medium Ground-finch. I feel that the bill is not deep-based enough for Large, and this gives it a more pointed look.

If you examine the images of Large Ground-finch in this article I wrote http://surfbirds.com/Features/darwinfinches/darwinfinches.html you will be able to see what I mean. Hope this helps.

Brian S

[joemorlan]

Thank you. That's a neat ID page on Galapagos finches.

I found something interesting. It turns out the Medium Ground-Finches on Santa Cruz Island are themselves bimodal in bill size and the two bill types exhibit assortative mating. The complete study with photos is online at:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2493575

Based on that I think I've got one of the large-billed morphs of the Medium Ground-Finch. I also sent the photos to Peter R. Grant who agreed with G. fortis.

I'm curious why you think this bird was a male.

[Brian S]

Joe

When I last saw these in 2006, I felt that in particular young or non-breeding males had bolder, blacker centres to the mantle. Your images seem to show the same.

Brian S

[j j]

I have made a set of photos that includes most of the species of Darwin finches, taken in August 2008:

www.flickr.com/photos/jjbirder/sets/72157614217328919/

The IDs took a lot of sorting out and I hope the images might help other visitors have a slightly easier ride with this difficult group.

John

PS I agree with Medium Ground Finch for the bird that started this thread.