The species (s?) of the characters are one thing that does not change-they always consist of the following…
Good Guys
Hares
Mice
Shrews
Voles
Hedgehogs
Otters
Moles
Squirrels
Badgers
…and a host of similar creatures NOT listed below
Bad Guys
Rats
Weasels
Ferrets
Stoats
Foxes
Minks
Martens
Marlfoxes
Moniter Lizards
The only exception to that rule is a character in the book, "The Bellmaker"