The yellow-billed (
Amazona collaria) and black-billed (
A. agilis)
Amazon parrots don't have much opportunity to be crossed in captivity because of their rarity -- yellow-billed Amazons are slightly easy to find, being as a few breeders were raising them, but the black-billed Amazons probably don't exist in the pet trade and are kept for conservation breeding. While both species come from Jamaica, they're from different lineages within the
Amazon genus -- the yellow-billed
Amazon's closest relatives are the spectacled, yellow-lored, and Cuban Amazons, and (if I recall correctly) the black-billed
Amazon probably evolved from something more like the mealy
Amazon (
A. farinosa ssp.). They didn't evolve by separation of one
Amazon population on the island into two -- they arose from separate colonization events by two
Amazon lineages that were already different enough to remain distinct, and thus diverge further over generations.
Hybrids between them would be fertile, as are the other hybrids within the
Amazon genus, but I don't know what the benefit to breeding them would be. While macaw hybrids can have interesting colors, especially when involving scarlet macaws, this is because macaws vary much more in body coloration. Amazons, save for a few very rare species, are essentially green birds with species-specific coloration differences on their heads, sometimes also their shoulders. Hybrids between species with very different head coloration typically results in birds with just subtle hints of their parents' markings blended into the green -- in other words, offspring are typically
less colorful than either parent species.
And to clarify for reference, macaw hybrids are not sterile, unless one of the parents is a Hyacinth (
Anodorhynchus hyacinthus), because that species is more distantly related to the others. Generally, hybrids within the same genus of parrots are fertile, with a few exceptions, one of which is Lovebirds (
Agapornis sp.), and that's only when the peach-faced is crossed with one of the eye-ring species. Hybrids within the eye-ring species, however, are fully fertile. With Lovebirds, I suspect that some DNA investigation would reveal that the genus really should be separated into two or three genera, but they've remained as one genus until then.
