Most of the extant species of American birds can hybridize and produce fertile offspring with at least one other species of bird. Mallards produce fertile hybrids with Pintails, Wigeon, European Wigeon, American Black Ducks, Mottled Ducks and a large number of other species. If your criterion of speciation were inabiility ever to produce fertile hybrids, there would be perhaps 4 species of duck on this continent. Orioles, warblers, etc are likewise mostly interfertile within the genuses. The major isolation mechanisms are geographical and behavioral, and when they break down, you get hybridization.
It's hardly surprising that the Darwin finches would do the same.
That was my first problem with that site (Boxhorn's) is that he fails to give a concrete definition of speication.
If your criterion of speciation were inabiility ever to produce fertile hybrids, there would be perhaps 4 species of duck on this continent.
Well, this is probably where we have a divergence of view points. My background is in Botany so I'd use the example of Oak Trees, and while the botanical nomenclature may make Pin Oak and Red Oak distinct species, the fact that they can produce fertile offspring makes them the same species, but different varieties in my mind.
Before they were domesticated, they were segregated by habitat, and I suppose you could say this was enough to make them separate species, that's just not how I (and most advocates of inteligent design) define it.
Owl_Eagle
(If what I just wrote makes you sad or angry,
Isn't it amazing that creationists will argue out of one side that evolution can't happen because the first member of a new species couldn't find a mate; then, without blinking, claim evolution is bogus because members of different species can interbreed.