It's an allopatric population. It's one of the great embarrassments of biology. The question "is this population part of the same 'species' as this other popula

It's an allopatric population. It's one of the great embarrassments of biology. The question "is this population part of the same 'species' as this other population" is simply not defined in biology when they are allopatric. Look at your country's bird identification guide. If you're in Europe or N. America you'll find lots of "species" that are just allopatric populations accompanied by some mtDNA / sound recording data claiming they're "sufficiently" distinct. It shouldn't be controversial to say that this is nonsense. The main problem is that it is challenging for conservation biology to admit that 'species' isn't well defined in allopatry. That is indeed unfortunate. But, science can't be politics. Think about it: there's nothing about the laws of physics, chemistry, or fundamental biology that implies that all populations must be clearly assignable to distinct categories. What biology says is that sexual eukaryotic organisms exist and they breed and distribute themselves more of less connectedly over space, and, stuff happens over time. Whether or not you can interbreed in sympatry is profoundly important -- loss of interbreeding is the basis of biological diversity. And allopatry is profoundly important -- it's the main way you lose the ability to interbreed. But two allopatric populations are just that: the organisms don't interbreed because they can't; they're not in "cruising distance". You could take two groups of individuals of any population you like and ship them off to islands on the other side of the world and they won't interbreed. They were part of the same "species" before their trip so presumably they still are when they get to their new homes. But the question of "when in the future should we say that they've evolved apart enough for us to call them different 'species'" is a question about what's convenient or useful, not a question about biological concepts or mechanisms. So it's not that studying the biology of allopatric populations isn't worthwhile -- far from it -- it's just that biology has a sentimental attachment to the idea that populations can always be assigned to "species". You can consider their ancestry as organismal pedigrees, and you can consider the ancestry of different parts of their genome, you can model it mathematically, you can collect genetic data and try to make inferences about it and about how the world they evolved in gave rise to it all. Population genetics, phylogeography, biogeography, phylogenetics etc are all extremely interesting and worthwhile. But with those subjects came confused "species concepts" stretching over decades trying to explain why some or other genealogical or phylogenetic criterion was the right basis to use to define the word "species". But the correct thing to do was much simpler: just accept that there is no scientific reason for the question "are these allopatric populations the same thing or not" to have any particular meaning, let alone answer. People who have written some sense among the decades of nonsense: Jürgen Haffer and and Ernst Mayr's geographical species, and Jody Hey's in his book "Genes, categories and species".