What contributed to the specification in darwin's finch theory

On his visit to the Galapagos Islands, Charles Darwin discovered several species of finches that varied from island to island, which helped him to develop his theory of natural selection.

Darwin's finches are a classical example of an adaptive radiation. Their common ancestor arrived on the Galapagos about two million years ago. During the time that has passed the Darwin's finches have evolved into 15 recognized species differing in body size, beak shape, song and feeding behaviour.