How has the green warbler finch adapted to the galapagos?

It was noted that the birds (finally understood to all be finches) had different shaped and different sized beaks. They also ate different types of foods. And they lived on different islands. The islands were too far for them to fly to.
They probably were all one finch long ago but they had to adapt to the food that was there. Some had thicker becks that worked the best on their island and others had much thinner beaks that worked best to get food on another island. These birds never bred with each other and really became separate species.