What trait variation did Charles Darwin observe after studying the Galapagos finches?

He discovered that finches in different environments had different shaped beaks

Charles Darwin studied the the beak structure of finches native to the Galapogos Islands. The study of these finches enabled Darwin to study and publish his theory of evolution by natural selection. Darwin realized the importance of the finches after leaving the islands while he was studying specimens he brought back with him. The trait he noticed was the differences in the size and shape of the finches beaks. He theorised that new species will arise when some factor causes a population to be divided.