As concerns digging ability, Goodwin (1935:148) reports that _Z. hudsonius_ makes its own burrows; these are short and close to the surface in the summer but longer, deeper, and below the frost-line in winter. Two captives used their forefeet and nails in digging a tunnel in the foot of soil that Goodwin (_loc. cit._) had placed in their cage. Quimby (1951:72) remarks that captives excavate soil by means of the front feet and throw the soil out behind; as the burrow deepened the hind feet were also utilized to throw the loose soil out of the burrow. _Zapus hudsonius_ climbs; Sheldon (1934:293) observed captive animals to climb over small evergreen trees in their cages. They moved with surprising sureness and agility, chasing each other among the branches or sitting for several minutes at a time on one of the limbs. Hamilton (1935:190) found that the mice ran over limbs and brush which were placed in their outdoor enclosure. Ordinarily _Z. hudsonius_ is nocturnal, appearing in the early dusk and remaining active until pre-dawn. Occasional individuals are abroad in daylight hours. Sheldon (1934:293) found in Nova Scotia that _Z. hudsonius_ is most active from early dusk through the night, but that it may be abroad in daylight as well. Her statements are based on trapping results, field observations, and observations made on captive individuals. Quimby (1951:73) found that _Z. hudsonius_ in Michigan is mostly nocturnal; however, he saw mice on a few occasions in the daytime. Diurnal activity seems to be increased in cloudy or damp weather; Quimby (_loc. cit._) almost invariably trapped more of these mice on cloudy, damp days than on other days. This jumping mouse usually is silent but does utter various sounds. Sheldon (1934:295) records squeaking and clucking noises. Quimby (1951:73) records the clucking noise described by Sheldon (_loc. cit._) and mentions also the squeaking and suckling sounds produced by the small young. This mouse is most vociferous when young or when about to go into hibernation. Sheldon (1938:327) writes that _Z. hudsonius_ makes a drumming noise by vibrating the tail against dry leaves. Many data are available concerning the hibernation of _Z. hudsonius_. In general it seems necessary for the mice to put on a certain amount of fat preparatory to hibernation. This fat is deposited in a thin layer over the inside of the skin, over the back, and in the body cavities. The thickest deposits are in and about the inguinal region.