Ferrets often use rabbit burrows as their dens.
In New Zealand rabbits are the primary prey of ferrets. Rabbits provide not only food but also shelter for ferrets, with rabbit burrows often becoming ferret dens.
Photograph: by Ilder by Malene Thyssen - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Ilder.jpg#mediaviewer/File:Ilder.jpg