172 NOKTH AMEKICAN FAUNA [No. 55 



Their habit of gathering material for building gives them the 

 name of pack rat and a reputation for dishonesty, as they often carry 

 away objects not intended for their use. Anything of a convenient 

 size, a cake of soap, a knife, a pen, or a watch may oe taken. Mouse 

 and rat traps and cartridge shells are often gathered up and used 

 for building material, and around camps it is customary to look 

 for lost objects in neighboring wood rat houses. 



The nests are neatly made, cup-shaped with thick, soft walls for 

 cold weather, always clean, even when made from shredded gunny 

 sack or a bit of old rope or the cotton out of a quilt. Sometimes they 

 are concealed by the heaps of sticky and rubbish and sometimes 

 placed on a shelf in the corner of a cabin. 



Wood rats are good climbers, not only in trees, but over rocks, walls, 

 and the rough boards of outbuildings, over roofs and perpendicular 

 or sloping surfaces. Their claws are short, but curved and sharp and 

 are used in self-defense as effectively as those of a cat. They are 

 quick and agile in running, dodging, and jumping. The bushy tails, 

 like those of squirrels, are useful in climbing, balancing, steering, and 

 turning abruptly. 



Their voices are rarely heard, although an old male caught in the 

 writer's hands and held securely against his will screamed and 

 screeched savagely. The young make a crying or whining sound if 

 taken from their mother. In other ways they are noisy, often making 

 a great racket running over floors, boards, and walls, or dragging 

 sticks, blocks, and tins over the floors. Their regular and unmistak- 

 able sounds, however, are the tapping or drumming with the sole of 

 one hind foot on the ground, floor, rock, or any smooth surface, a 

 slow tap, tap, tap, at about 1-second intervals. The speed and force 

 of the taps vary with the occasion, sometimes quick and hard, again 

 soft and slow with evident variation of expression. The sound is 

 made by both males and females, not only when alarmed, or 

 disturbed, but often when alone and unsuspicious. 



The animals have a strong musky odor emanating from an elon- 

 gated abdominal gland, a thickened strip of skin that secretes a 

 musky, oily substance that undoubtedly enables them to recognize 

 the presence of their own species and possibly to distinguish indi- 

 viduals. A cave, room, or box, occupied by them is usually notice- 

 ably musky, even to our feeble noses, although not unpleasantly so. 

 No animal could be neater, cleaner, or more sanitary in habits. The 

 dry, black, elongated pellets are mostly placed in definite corners 

 not used for other purposes, and the urine is deposited on the points 

 and edges of certain rocks away from the nest or along the face of 

 the cliffs, where it forms white calcareous encrustations on the rocks 

 which may be seen from a distance and are always evidence of the 

 presence of wood rats. In course of years this deposit becomes 2 or 3 

 mm thick, as hard as rock, and with every appearance of a geo- 

 logical formation. In some of the dry caves old deposits of the 

 pellets have become solid, black, waxy masses with the appearance of 

 asphalt, and might also be easily mistaken for geological deposits. 



Breeding habits. The females have 4 mammae, arranged in a 

 quadrangle on 2 parallel mammary glands in the inguinal region. 

 The young, generally 2, but sometimes 3 or 4, are born usually in 

 spring or early in summer, and are nearly full grown by autumn. 



