Eadie (1949:307), Grizzell (1949:75), Sheldon (1934:299), Schwartz (1951:228), and Sheldon (1938:331) all agree that the hibernating mouse rolls up into a ball-like shape (resting on its head and pelvis) with the head between the hind legs, the nose against the lower belly, the forefeet curled on the chest, and the tail curled around the head and body. A marked loss of weight occurs immediately after hibernation begins, and then reduction in weight is slow and regular. (See Hamilton, 1935:194 and Quimby, 1951:84.) Sheldon (1934:297) cites a letter from Vernon Bailey in which he remarks on the necessity of abundant moisture and saturate air for hibernating jumping mice. Bailey writes "... they will awaken at times famished for water and will drink and drink before going back to sleep." Hamilton (1935:195) thinks that in the Ithaca area of New York these mice probably leave their winter quarters in the second half of April and that in southern New York and Long Island they emerge considerably earlier. Quimby (1951:82) and Bernard Bailey (1929:163) report that males appear earlier in the spring than do the females. Quimby (_loc. cit._), by recording the sequence and dates of phenological events and appearance of _Zapus_ in several years, was able to predict fairly accurately the time of emergence of _Zapus_ in a succeeding year. In Minnesota, jumping mice emerged late compared to other hibernating rodents. _Enemies._--V. Bailey (1927:119) reports that A. K. Fisher found 50 skulls of _Zapus_ in barn owl pellets taken from the towers of the Smithsonian Institution, Washington, D. C. Dearborn (1932:32) reported mink as having fed on jumping mice. Surface (1906:197) records taking a _Zapus_ from the stomach of a rattlesnake. Pearson and Pearson (1947:138) found remains of _Z. hudsonius_ in pellets of barn owls. Quimby (1951:74) reports two cases of predation on _Z. hudsonius_; one was by a northern pike, _Esox lucius_ Linnaeus and the other was by a weasel, _Mustela_ sp. Vergeer (1948:91) collected a green frog, _Rana clamitans_ Latreille, which had eaten a jumping mouse.