We ask that you have a mainly human picture with the squirrel picture on your app--its okay if it doesn't look great! But that's more or less a requirement.
Once you're in the group you can draw the squirrel form more often if you'd prefer.
(This is partially why i had an animal and a human for the group; i thought it'd be good exploration for all kinds of artists to get at least a small taste outside their comfort zone).