The reason why Huck didnt tell anyone of Jim escape is because both are outcasts and Huck have family problems and other society problems his father is abusive and alcoholic who doesn't care for him, and the two women who sometimes care for him try to change his character. So he dosent have to tell anyone of this cause it none of the buisness to know about this and another reason is because Jim is a human being also and he needed freedom and desverve peace cause he's also in a human society. While Huck faces few legal barriers in his own quest for personal freedom, the stakes are much higher for Jim, since it is against the law for slaves to run away. Jim think it's the right thing to do. This explain that Huck charactor is has a sunny disposition and a well developed and matural sense of morality.
Animal characters usually exhibit what you've described. Stereotypes regarding animals such as the lion being courageous or the fox being sly are usually found as traits of the characters themselves when created as anthropomorphic characters.
