Staunch.

Rabbits (says Mr. Lockley) are like human beings in many ways. One of these is certainly their staunch ability to withstand disaster and to let the stream of their life carry them along, past reaches of terror and loss. They have a certain quality which it would not be accurate to describe as callousness or indifference. It is, rather, a blessedly circumscribed imagination and an intuitive feeling that Life is Now. A foraging wild creature, intent above all upon survival, is as strong as the grass.

Richard Adams, from Watership Down