The beaver is still working away at the big cottonwood. He, or she, made the first deep cut into the tree on the creek side, which is the direction that it would be most convenient for the tree to fall, as that would bring a large amount of food and dam building materials right into a convenient location across the creek. Most recent cutting, however, includes cutting at the back side of the tree, opposite the deep cut on the creek side. At the rate that the work goes forward, it will likely be several weeks yet before the tree will fall. Herb and I visited the area on Saturday, January 30^th. My son, Mark, constructed this video from the pictures we collected at that time: 

One of the captions on my video states that the beaver does most of his work at night. Actually, all of the work on cutting this tree has been done at night. My cameras have collected hundreds of pictures as the cutting has progressed.

Karen found a very comprehensive reference to the biology of beavers, dealing with their special adaptations and habits (see: https://www.aphis.usda.gov/wildlife_damage/beaver_damage/downloads/Baker%20and%20Hill%20Beaver%20Chapter.pdf.)  

Beavers are North America’s largest rodents, very powerfully built, with unique anatomical adaptations to their ecology and lifestyle. Notice this beaver’s large webbed hind feet, built to drive it forward in swimming. Its strong jaws and large front teeth built like chisels are adapted for cutting wood, its main food and building material for houses and dams. It closes its lips behind its incisors to keep out water when swimming underwater. Its eyelids are transparent to allow vision when closed. When under water, its heart rate slows to allow the animal to remain under without breathing for up to 15 minutes at a time. The beaver’s digestive system is especially adapted to digest wood, and its food makes two trips through its digestive tract, as the first round of digestion results in a semi-liquid greenish substance which is eaten and passes a second time through the digestive system.

Beavers live in colonies, which typically are extended family groups. Young beavers remain in the family until they are about two years of age; they then leave to search out homes elsewhere. During this time of dispersal of both males and females, they are called floaters, and must find mates before establishing permanent residence in an area. Perhaps our beaver is just such a floater. I hope to be able to monitor it with my trail cameras as long as it remains in our area.