Description: When Darwin visited the Galapagos Island he collected a number of bird species that he brought back to England. He presented them to ornithologist John Gould thinking they were a variety of birds and he was told that they were all different varieties of finches. This led Darwin to speculate that a population of finches had arrived on the islands and had adapted to different climates through natural selection. However Darwin was never able to observe evolution taking place. Researchers Peter and Rosemary Grant have been observing evolution of Galapagos finches for the last 40 years. One of the most famous studies involved the change in beak depth of medium ground finches during times of drought. Birds that had small beaks were unable to open the dry seeds causing microevolution in the surviving birds.
Web Resources: Peter and Rosemary Grant Research - Wikipedia, The Beak of the Finch - HHMI