A skulk is a group of which animals

Foxes
Foxes are small-to-medium-sized, omnivorous mammals belonging to several genera of the family Canidae.

Foxes are slightly smaller than a medium-size domestic dog, with a flattened skull, upright triangular ears, a pointed, slightly upturned snout, and a long bushy tail (or brush).

Read more...https://en.wikipedia.org/wiki/Fox

Books
Exploring the World of Foxes