Answer
Charles Darwin discover the finches in Galapagos in 1831. He noticed that the finches beaks were different compared to the finch's in Ecuador.
Galapagos finches
he found it
Charles Darwin discovered that finches in one place have different beaks in another place yet the same type of bird thus the theory of adaptation was born
Charles Darwin
finches
Since Darwin found many species of plants he found many species of finches. Those species, just like the warbler finch, were found on the Galapagos Islands.
He didn't discover much other than the interesting variations in the shapes of the Galapagos finches' beaks. He formulated the famous Theory of Evolution, however, which might answer the question.
Variation
No. Charles Darwin hypothesized about evolution.
Galapagos Islands are the islands where Charles Darwin observed variation among organisms.