How do the Galopogus Finches (Darwin's Finches) prove MACRO-EVLOUTION?

I've found a lot of info on how they support MICRO-EVOLUTION, but so far I don't see how it really supports MACRO-EVOLUTION. I need to know how it supports Darwin's Theory of evolution that a Creationist can't argue with, or at least something that they don't already agree with, like MICRO-EVOLUTION. Please help if you can! Thanks!