Could there be a "Move to" option placed directly on individual creatures' profile pages, too? You could click it, and it would bring a menu with the options to move that creature directly to either the trade clan or one of your other clans, or, if it's already in a clan, to change clans or remove it from clans entirely (send it back to the "creatures without a clan").
I only now JUST noticed the "Clans" link on creature profiles which will tell you what clan it's already in, and, if it's not in a clan, will give you the option to move it to one!
So this could just be an improvement on what's already existing, and could include the option to move a creature from one clan to another (instead of just removing it from the clan it's in), or to add it to the trade clan instead.This feature would be most useful on the creatures not in any clan, but could be used elsewhere, too.
