I have a parrot smaller than African Grey Rebecca's African Grey (mine is a
Cherry Head Conure), who is likewise out of his cage when ever I'm home.  My
bird, Cory, does not have clipped wings, however, so he stays close to the
ceiling - most of the time - and the ferrets stay close to the floor - most
of the time.  The ferrets are are hardly aware of Cory (although he watches
them from his aerial perch with his usual vigilance for the various
creatures who share his abode).  Every so often, though, parrot and ferret
end up on the same "altitude," and both are ready to go at each other,
mouths open and ready for combat!  Cory is smarter, but the ferrets are
stronger, and I don't want to find out what might happen....
 
If allowing your birds their flight feathers is impractical, Rebecca, you
might consider a "ferret gate" for your kitchen door.  I've put one up
between my pantry and my kitchen, as there are holes in the pantry walls
that I'm afraid my ferrets would disappear into (I don't know what's behind
them!).  My gate (a piece of smooth wood) is about 2 feet tall, and I've
attached it at each corner with a hook-and-eye from the hardware store.
People can step over it, cats can jump over it, but it keeps the ferrets
out.  Of course the ferrets were annoyed when I first discovered the holes
and put up the gate, and they made many determined efforts trying to
jump/climb/remove the thing.  But I gave them a stern "No!" when ever they
made an attempt, and eventually they forgot about the "forbidden kingdom,"
as there are enough other interesting objects of destruction in my house!  I
sometimes detach the gate when the ferrets are in their cage and I'm running
in and out of the pantry a lot, but I've gotten used to stepping over it, so
I rarely take it down any more.  I hope this is helpful.
[Posted in FML issue 1278]