[This section was written by Kelleen Andrews, with contributions from
me and others.]

Dominance fighting is normal in ferret introductions. The severity can
range from nearly nonexistent to all-out war.  Prepare for the worst,
and then anything less than that will seem like a piece of cake!
Patience is the most important virtue.  Often all is well in 3-14 days
but sometimes peace is not achieved for 3, 5, or even 7 months.
Ferrets that have been away from other ferrets for two years or more
tend to take longer to adapt.  Keep in mind that your final goal is
well worth the work and that having two or more ferrets that have each
other to love and play with is the greatest joy you -- and they -- may
ever know!

It's often easier to introduce a new ferret when the others are still
fairly new themselves.  A ferret who's used to being an "only ferret"
or a group which has been together for several years may resist the
newcomer more strongly.  It's also sometimes easier to introduce two
at once, to divide everyone's attention.

Many techniques can be used to ease the transition.  No one technique
works on all ferrets; a combination of them has the best chance of
success.  Reassure all ferrets often that everything is OK and they
are loved.

* Most important, make sure the newcomer is disease-free and current
  on vaccinations [9.2] before any interaction. You may choose to
  quarantine the newcomer for one or more weeks.

* If you can, and if you know that all the ferrets at the breeder or
  shelter are healthy and haven't been exposed to ECE, take your
  current ferret along with you when you pick out a new ferret so he
  can choose his own new friend.  Also, a pair often blends into the
  existing group where a single may have more problems.  A kit
  newcomer can be a plus but requires more precautions. Since a kit is
  tiny, if the established ferret is too rough you may need to cage
  it separately until it grows larger.  A kit that is constantly
  attacked and dragged around by an aggressive ferret may be seriously
  injured or become so traumatized as to want nothing to do with other
  ferrets.

* Make sure the first introduction takes place in a completely
  neutral area -- not just an unused room in your home, but
  preferably in someone else's home or someplace else neither ferret
  has ever been near. It also helps if other ferrets and distractions
  are there. One other ferret may be seen as an enemy whereas a group
  is seen as a party!

* If an immediate introduction feels uncomfortable to you, keep the
  newcomer in a separate cage near your current ferret's cage. Have
  supervised visits often, and let one ferret out at a time for
  playtime. The new guy can then get used to the new surroundings and
  the established ferret will not feel he's being punished.  Switch
  their bedding back and forth so they become accustomed to each
  other's scent.

* Give the ferrets baths immediately so they smell the same. Bathing
  them together may help since misery loves company. You might also
  put vanilla extract on their noses to confuse their smelling and
  bitter apple on their necks to discourage biting. Smearing
  Ferretone or Nutri-Cal on their faces will encourage licking rather
  than biting.

* Start out by holding the ferrets and letting them sniff each other.
  Gradually, as you feel comfortable with it, give them more freedom
  to interact with each other.  Expect fighting, but always supervise
  in case it becomes violent.  When you pull wrestling ferrets apart,
  if the loser goes back for more they are probably just playing
  rough.  A ferret that bites with a darting motion and shakes his
  opponent roughly or tears at his skin is being more aggressive than
  normal dominance struggles.  If you leave them alone, one ferret
  can end up with a neck covered in scabs, infected or worse.
  Usually when a ferret is being hurt he'll get very loud vocally,
  often screaming, but this is not always the case, so constant
  supervision is a must.  (Some ferrets scream when they're not being
  hurt, or even when they're the ones attacking, so don't assume the
  loud one is the one being picked on.)

  When undue aggression occurs, immediately scruff the attacker with
  your hand, or better yet with your mouth, and gently shake
  him. Scold him loudly, right up close.  Afterward put the attacker
  in his cage for a time-out.  Don't hit him, even tapping his nose,
  since that will only make him afraid of you, and he's already under
  stress.  If scruffing, scolding, and cage time don't work, he
  probably needs a little more time to adjust.  Also be sure to find
  the newcomer and reassure him he is safe and loved.

  If the ferrets groom each other, often around the ears or neck, it's
  a sign of acceptance, but do not leave them unsupervised until
  you're positive there is peaceful integration.

Unfortunately in very rare instances peace is never achieved and a new
home may need to be found for the newcomer.  Of course you'll want to
be sure the new home will be understanding and loving, but also make
sure the prospective new owner is aware of the problems the ferret has
had getting along with yours, since even if he wasn't the aggressive
one it will affect his relations with other ferrets.  You don't want
him to end up being passed from house to house, never able to fit in.

Sometimes, even after an established ferret and a newcomer have
stopped fighting, the first ferret may start to act depressed,
especially if he's used to being an "only ferret".  Ferret psychology
is still an undeveloped field, but most people interpret this glumness
as jealousy or resentment of the new ferret.  Be sure to pay plenty of
attention to all your pets, and give the depressed ferret a couple of
months to adapt.  Chances are he'll come to see the new ferret as a
playmate instead of an interloper.  In extreme cases, you may need to
resign yourself to only having one ferret, and find a good home for
the other(s).