The stock of the original Danish black squirrel is shrinking because they are mixed with red squirrels.
In the language of genetics you call the two different squirrels for haplo types. You can compare it with people with blue and brown eyes. Since the black and red squirrels are the same species, they can mate.
In the whole country pockets are left with black squirrels, but almost everywhere there are also red squirrels. The only place where the black squirrel continues to live in isolation is in the woods at Faaborg, and on Langeland, where we have set them out. In the long run, the red squirrels will also reach the forests at Faaborg.