That sounds like bunk. Has someone really tried to get every suspiciously similar but distinct species to mate? If I go and get these two to mate are they really going to delete one of the species:

https://en.wikipedia.org/wiki/Altamira_oriole

https://en.wikipedia.org/wiki/Baltimore_oriole

Just Think it logically there are millions and millions of animal species alone. The number of combinations is astronomical. Did someone really try out each combination? It’s silly. Of course not.