I remember thinking that he described the behavior of the rabbits really realistically (except for all the anthropomorphism, of course). I always intended to read Tales from Watership Down but haven't gotten around to it yet.
Watership Down is about the journey of a group of rabbits from Sandleford Warren, which is destroyed to make room for a housing estate, to safety at Watership Down and how they established their warren there. It's fictionalized for the purposes of plot of course - Adams even invented a language and a very compelling origin story and mythology for the rabbits - but the underlying motives and actions are believable and realistic.
The realism is based on actual research - Richard Adams gives credit to the book
The Private Life of the Rabbit by R.M. Lockley, which is a very interesting nonfiction book on the behaviour of wild rabbits. Lockley based the book on years of observation of rabbit warrens in England and Wales.
It's not just the rabbits' behavior which is realistic. The setting is not just realistic, but entirely real. Adams placed the migration of the rabbits in an area he knew well, in the counties of Berkshire and Hampshire in England. There was an article about
Watership Down a few years ago in
British Heritage magazine in which they traced the route of the band from Sandleford to Watership Down, and everything was there exactly as Adams had described. What is interesting is how small an area it really is - a bit over five miles from Sandleford to Watership - but from the point of view of a small rabbit, that's an epic journey.
There's a website called "The Real Watership Down" at
http://www.lionking.org/~watership/ which has pictures and a map of the area.
Tales of Watership Down wasn't bad, but it's basically a collection of short stories, half of them being about the rabbits of the warren after the events of the first book, and the other half being mythological tales told by the rabbits expanding on the exploits of El-ahrairah, the First Rabbit.