The definition of a species is creatures or plants that can successfully mate and have full functioning offspring. Thus, there are many species of birds but they are all birds. There are many species of mammals but they are all mammals. The finches are a good example of genetic drift.
To be clear.
Species is easy, speciation is another story all together.
A simple search of the definition would yield results that show, based on your posts, that you have no clue what you are talking about.
Best of luck.