Yesterday, Herb and I again visited my trail cameras in Glen Canyon Regional Park, continuing our observations of the goings on at the beaver tree. In searching my notes, I see that I noticed this large cottonwood that is being cut by a beaver on November 23, 2015. I first photographed that tree on December 14^th, 2015 .

At that time I would estimate that it had been worked on, intermittently, by one or more beavers over a period of least a month. This second picture was on my trail camera today. Note that it is dated January 23, 2016.

 Each time that we visit the area, we see many smaller trees that have been cut, all birches and cottonwoods. There are at least two beaver dams on the creek, one quite low at the old fording area and a higher dam that is built against a large fallen pine tree.

Since there is no lodge, the beavers must be living in a bank den. All of their work on land seems to occur at night, as all of  the hundreds of pictures of tree cutting have been night-time pictures.

 Daughter Karen has enjoyed researching the literature on beavers and their behaviour. She has given me permission to share her findings with you. She writes :

I've taken quite an interest in beavers since you started documenting that "beaver tree". I just marvel at a single beaver -- which it seems to be, in this case -- tackling such a huge project! You tell me that the cottonwood tree, when carefully measured, comes to 107 inches in circumference. Divide that circumference by 3.14, and the tree would have a diameter of 2 ft. 11 in. It will be interesting to find out how long it takes the beaver to cut this tree down, from when it started (in middle or late November?).

At your request, I'll share some of the beaver information I've been finding.

The fact that your beaver is working at night is typical of them. They are crepuscular and nocturnal, so they are most active from dusk through till dawn. Their vision is believed to be poor, both on land and in the water, and they rely far more on their sense of smell.

Bears are listed as predators of beavers. Also otters, lynx, mountain lions, owls, and eagles. And it was thought that wolves were major beaver predators. But I found an article in the online version of the Boston Globe newspaper -- http://www.boston.com/news/local/articles/2009/02/01/coyotes_not_wolves_are_natural_predators_of_beaver/ -- claiming that coyotes, rather than wolves, are the major beaver predators. So I expect your beaver is vigilant against the local coyotes, especially.

Beavers are highly territorial, and do a lot of territory marking, leaving their scent in strategic places. They snarl, and they slap their tails on the water in warning, and occasionally they fight. When they feel trapped and afraid they will be aggressive and will bite -- even humans -- and they have been known to attack dogs. Hikers in your canyon would be well advised to keep their dogs on leash.

The large front teeth of beavers are a dull orange on the outer surface. That side of their teeth has extremely hard enamel, whereas the inside surface of their incisors is not so hard. As the teeth grow (which they do during the whole life of the animal), they wear down mostly on the inside surface, making them very sharp and chisel-shaped.

Those large teeth allow the beaver to close its mouth behind them. With lips closed underwater, a beaver can gnaw and carry branches.

An adult beaver will swim for only 14 to 23 minutes at a time, leaving the water in order to bring its body temperature back up, which takes about 60 minutes.

Swimming and diving adaptations include ears and nostrils with valves that close, and eyes that have clear eyelids. A beaver can stay underwater for usually up to five or six minutes, with 15 minutes being the known limit. Its lungs and liver are both large, the lungs to hold air, and the liver to store oxygenated blood. When diving, their heart rate slows to almost half its out-of-water speed.

(I was amazed to learn that even the human heart will slow down when underwater. In beavers and in humans, this reflex is triggered by immersion-sensitive nerve endings in the mouth and nose areas.
For a human, upon immersion of the face into cold water for 30 - 40 seconds, the heart rate will slow by 10% - 40%. The colder the water the greater the effect. Medical professionals have found this useful when treating a patient with an abnormally fast heart rate; even the placing of a cold wet towel, or plastic bag containing ice water, on the face is effective. Children and young adults respond better than older adults.)

The interesting book in which I learned the information above about human heart rate slowing underwater, is called The Beaver: Natural History of a Wetlands Engineer, by  Dietland Müller-Schwarze. Regarding underwater adaptations in beavers, the author says: "The cloaca is the single opening for the reproductive tract, excretion, and scent glands. This arrangement is thought to minimize infections when swimming in foul waters."

Beavers have special adaptations for digesting their high-fibre diet. They share with koalas and wombats a special gland that secretes into the stomach. They are "hind-gut fermenters"; they have a three-lobed cecum containing microbes to aid in digestion. And they share with other rodents and with rabbits the consumption of their own excrement, so that a meal passes through their digestive system a second time. (This is not feces that they eat, but partly digested food.) In the daytime they reingest this soft green excrement directly from their cloaca -- chewing before swallowing (whereas the rabbit swallows pellets whole). This has been observed in beavers as young as ten days old. Dietland Müller-Schwarze writes: "...only 6% of eaten bark was digested after 11 hours (first defecation after a meal), but 88% was digested by the second defecation on the second day."

I found good information also in an article printed in the January/February 1997 issue of Wildlife Art, written by Michael McIntosh. I'll quote three paragraphs from it, in closing:

"In part, gnawing is the beaver's livelihood, for it feeds primarily on the bark and cambium (the inner bark) of woody plants -- willow, cottonwood, sycamore, alder, oak, beech, birch, hickory, aspen, whatever grows near water. Beavers eat a fair amount of aquatic vegetation during the warmer months (and they love corn as well), but bark from twigs and branches cut and cached beforehand is virtually their sole fare in winter. They don't hibernate, and the average beaver needs about two pounds of food every day."

"...They prefer trees with trunks two to eight inches across, and one beaver can fell a five-inch willow in about three minutes. Two or three may collaborate on a larger project and stay with it for more than a single night. Beavers in British Columbia once toppled a 110-foot cottonwood that was just over five and a half feet in diameter. I've seen some two- and three-foot beaver-cut stumps and quite a few similarly sizable trees that were in the process of being felled.

"Having taken down my share of trees with a chainsaw, I'm continually impressed by the fact that beavers do it with their teeth. Typically working on the side nearest the water (which is both most convenient and, because of how streamside trees tend to lean, most likely to topple it in the best direction), they rear up on their hind feet, lean against their tails and start gnawing, cutting a notch and then another about three inches lower. Bracing their upper teeth and using the lower ones as slicing chisels, they cut away wood between the notches chip by chip till the tree breaks and falls. The animals are agile enough that they very rarely get coldcocked by one of their own falling trees. Only once have I ever found a log with a beaver skeleton crushed underneath."