Mimus melanotis – San Cristobal mockingbird (aka Chatham Island mockingbird). Mr. Rintoul writes that the San Cristobal mockingbird "is found only on the island of San Cristobal and nearby Pitt Island in the Galápagos Archipelago. It was one of the first animals encountered by Darwin when he arrived on San Cristobal (which British sailors called Chatham Island) in 1835. Other similar-but-different species of mockingbirds, collected by Darwin on other islands in the archipelago, provided some of the first sparks for his ideas about speciation and common descent. See here and here."
I was drawn to this picture while mining some old contest pictures for this post. When I was in the Galápagos in 2006 (see here and here), I did not manage a photograph of a single finch or other small bird, save one or two that are not endemic.
