Hair loss at the base of the tail often, but not always, is a sign of an
adrenal tumor.  Have the vet check for other possible causes, but consider
that one too.
 
Although you are a long drive from NH, one of the best ferret vets in New
England has an animal hospital in Weare, NH.  Dr Mike Dutton, often seen
posting here, is a fantastic ferret vet.  Well worth the drive.  His number
is 603-529-4999.
 
Dick B.
[Posted in FML issue 1599]