February, 1922. 



The Canadian Field-Naturalist 



31 



and round and the tail very short, being only 

 three-quarters of an inch in length and covered 

 with fur. The name "boomer" was given to 

 these animals from the peculiar booming noise 

 made at night. 



They are found only on the eastern and western 

 slopes of the mountains of the Pacific Coast in 

 Canada and the United States of America. So 

 far, the most northerly record for these animals is 

 the Eraser Valley, thence they extend southerly 

 to northern California. 



These animals have been known to climb trees 

 a few feet in search of food, but, judged from the 

 structure and short hind legs, they cannot be 

 very expert climbers. 



They travel considerable distances from burrows 

 and have frequently been caught in traps set in 

 sloughs for muskrats. They have been found 

 living at an altitude of 3,000 feet, near Coalmont, 

 B.C. 



After removal of the skin, the body resembles 

 that of the mole more than that of the muskrat, 

 woodchuck or squirrel. The joints are loose and 

 flexible, and all parts of the head, neck, body and 

 legs are encased in tough, powerful muscles. The 

 neck is extremely short and so heavily covered 

 with muscles that in diameter it is the same size 

 as, or larger than, the head. The shoulder blades 

 are situated only one-half or three-quarters of an 

 inch distant from the base of the skull, so short 

 is the neck. The skull is flat and broad, and the 

 lower jaw attached by powerful muscles. The 

 bones of the hind legs are short for the size of the 

 animal and from the muscular development i+ 

 would appear they are much less used than the 

 strong fore-legs which are used in digging the 

 wonderful tunnels these animals are known to 

 make. The tail is very short, being not more 

 than three-quarters of an inch to one inch in 

 length, and is curved upwards like that of the 

 rabbit or hare. The eye is dark in colour and 

 small in size, the eyeball measuring only 7-32 to 

 \ of an inch in diameter, indicating a dark-loving 

 animal. The claws are long and strongly made 

 for digging in the earth. The skin is loosely 

 attached to the body as with the marmot. Two 

 small scent bags are situated at the base of the 

 tail and from these a peculiar musky scent is 

 produced when the animal is disturbed or excited. 

 The weight of an adult mountain beaver runs 

 from two to three pounds, but this weight will, 

 of course, vary with the season, as these creatures 

 are fatter in the fall than in the early spring. 

 The teeth, which are strong and chisel-like, are 

 used in the same manner as are those of the 

 ordinary beaver in cutting brush, sticks, roots 

 and salmonberry canes for food, and for gnawing 



through roots, etc. 



When walking about in the vicinity frequented 

 by the mountain beaver one may be surprised, 

 when least expecting it, by the sudden sinking 

 of the foot into the ground for a distance of six 

 or eight inches; on examination, it will be found 

 that this is caused through having trodden on 

 top of a mountain beaver burrow when it has 

 approached close to the surface of the ground. 

 If the burrow is followed for any distance, it will 

 be found to twist and turn in an extraordinary 

 manner, usually keeping from four to twelve 

 inches under the surface, but. in some instances, 

 running to a depth of from three to six feet. The 

 burrows are about six and a half to seven inches 

 in diameter and run for great distances, with 

 openings every few feet. After careful study, 

 examination and excavation of numerous burrows, 

 I have been led to the conclusion that they are 

 so constructed for a dual purpose; firstly, to 

 secure ready access to food supplies and feeding 

 grounds and, secondly, to enable them to escape 

 more easily from their enemies, the marten, mink, 

 skunk, owls and other creatures which apparently 

 feed upon these animals when opportunity offers. 

 In nearly every instance when the burrows have 

 been examined and traced, it was found that 

 they started from a ravine in which a creek flowed, 

 a slough or other damp place where there was a 

 constant supply of fresh running water, and 

 the lower tunnels are so constructed as to be the 

 outlets for little trickling streams of water; in 

 some cases, carefully made canals have been 

 placed to guide the course of the water from the 

 mouths of the burrows. Apparently water and 

 plenty of it is essential to the well-being of the 

 mountain beaver, as it is found only in regions 

 where water is abundant and easily obtained. 

 Mountain beavers are only semi-hibernating, and, 

 while they do not come out much in the winter 

 time, yet they have an abundant underground 

 fresh-water supply, no matter how cold the 

 weather or how deep the snow may be. Far down 

 in their subterranean chambers they live during 

 the cold months amply supplied with water and 

 food. From December until March, they are 

 sluggish and do not come out of their burrows 

 very much; in some instances they have been 

 known to block up (late in the falH some of the 

 entrances to the burrows. 



In one set of burrows examined, a portion in 

 an area of 50 x 50 feet contained sixty-eight 

 entrances to burrows, and, farther down the 

 mountain in a ravine, these burrows had no less 

 than six outlets out of which streams of water 

 poured. One of these I found only through 

 hearing the water gurgling underground, and. on 



