Linked from
The 19 pages that link to Darwin's finches, each with the reason it gives.
BiogeographyBroader topic: The classic case of island colonization followed by adaptive radiation.
BeakBroader topic: Their beak variation is a classic case of adaptation to different food sources.
FinchBroader topic: Their bill diversity makes finches a celebrated example of adaptation.
BillBroader topic: Their bill variation illustrates adaptation to distinct food sources.