I think it may have more to do with handling technique, pair bonding, hormonal behavior and how they trained their original families. Clever, beautiful, destructive and fascinating little jewels. One of them also says "Good morning pretty bird, Good morning pretty blah!" very funny little bird. Two of them are pretty plucked one has a unibrow and looks a bit like a Klingon the other two are in perfect feather but still very aggressive and cage protective.
http://i201.photobucket.com/albums/aa264/Firefly_mom/MEMO0009.jpg