When startled by a passerby, the beaver will slap its tail into the water. Beavers will tend to emerge from their lodges or the water only a night. This will serve as a warning to all other beavers, ensuring that all know that danger is near. Coupled with the beaver's excellent swimming ability (1/3 AP per combat hex in the water) and the beaver's lodge being accessible only through an underwater doorway, an effort to catch or kill a beaver is extraordinarily unlikely except with the use of traps. Beaver pelts are fairly valuable.
The beaver is included in the bestiary only because at night, if encountered out of water, it can be quite dangerous, though a beaver is unlikely to maintain a melee for more than a single round (it will if trapped).
The Castoroides, or giant beaver, can be very aggressive, even during the day. The tail slap produced by a Castoroides is loud enough to break a spellcaster's concentration, ruining a spell, and to cause deafness for 1-4 rounds to anyone within 2 combat hexes (10 feet) who fails to make save against magic. As well, if the tail slap is heard, other giant beavers in the pond will move towards the slap and aggressively assault any invaders they encounter.
Beaver families of all sizes consist of an adult male and female, along with their kits and yearlings. Offspring may continue to serve the same beaver pond as their parents, and may built associated ponds that share water sources. Whole beaver "towns" may form in areas where they are undisturbed, so that six to eight lodges may be found in a single square mile, typically spaced hundreds of yards apart.
Sources that claim a high intelligence for some beavers, that they wear clothes, are highly educated and that they trade for goods with outsiders, is unsubstantiated nonsense.