Their dams give really good supplies like Pearls, cementing paste, mushrooms, etc. Put a bed near the beaver dam, go collect your items from the beaver dam, watch yourself die. Then respawn at the bed and collect your items from your dead body. Otherwise if you go up to a beaver dam and try to get supplies they're just going to kill you and you'll lose your stuff. If you bring a dino, leave it on passive as the beavers are very vicious and can easily kill anything especially since they're in groups.