In years past, hollows were made in fields, then planted with trees, to provide a suitable habitat for a fox to site its den. And all for the entertainment of the landed gentry, who wanted to chase foxes for so-called 'sport'. Known as 'coverts', the local countryside is still dotted with these sites.
You might notice (you're not looking closely enough if you don't) some bloody awful-looking signs of attempting to clear dust marks. What on earth is going on here I do not know. They're not noticeable until I upload the photo.