Beavers are known around the world for their high quality warm fur. The beaver lives in a den made of mud and sticks with entrances under water to prevent unwelcome intrusions. The dens are moist, but stay warm even during the prolonged cold of northern winters. Beavers are active throughout the year, however they are primarily nocturnal and most likely to be observed in the evening as they begin their work. Late night tail slaps can be heard at great distances to signal others of impending danger.