Chipmunk (genus Tamias).—Remains were found in a male ermine in New York on May 14, 1932 (Hamilton, 1933:330), and Seton (1929 (2):602) records a chipmunk at Lake Couchiching, Ontario, that was pursued into the water by an ermine.
Deer mice (genus Peromyscus).—As shown by Hamilton (1933:33) and Aldous and Manweiler (1942), Peromyscus was second only to microtines in numerical abundance among the food items of ermines in New York and Minnesota. Peromyscus and microtine rodents were brought to a den of the diminutive M. e. muricus in early August, in Fresno County, California, according to Ingles (1942). He observed that an Alpine chipmunk was active under and around the tree and that juncos reared young 40 feet from the den but that the chipmunk and juncos were unmolested by the ermines.
Lemming (genus Lemmus).—One was recovered from a female ermine (with milk in her glands) at Laurier Pass, British Columbia (Sheldon, 1932:201).
Red-backed mouse (genus Clethrionomys).—Criddle and Criddle (1925:146) record that on "May 31, 1921.—Saw a Bonaparte's weasel capture a Red-backed Vole after a long hunt during which the pursuer never once lost track of its victim."
Meadow mice (genus Microtus).—As shown by the data of Hamilton (1933:333) and Aldous and Manweiler (1942) recorded above, Microtus is the item of first importance in the diet of the ermine in New York and Minnesota. Criddle and Criddle (1925:146) write concerning the vicinity of Treesbank, Manitoba, that "October, 1918.—Following a severe outbreak of mice in 1916-17, Bonaparte's weasel increased enormously and very soon reduced the rodents to comparative rarity. This resulted in a scarcity of food for the weasels, which in their turn became greatly reduced in numbers."
Old World rat (Rattus).—Bishop (1923) found two headless rats near a nest of this species in Albany, New York.
Pika (Ochotona).—Dixon (1931:72) at Milner Pass, Colorado, on July 20, 1931, saw an ermine, of the subspecies muricus, following a three-fourths grown pika by scent and outrunning the pika. The pikas worked a relay system and the weasel abandoned the trail when the fourth pika became the object of the chase.
Cottontail (genus Sylvilagus).—Hamilton (1933:33), as noted above, found remains of cottontail in the digestive tracts of ermine that had been trapped for fur in winter. Possibly these remains were bait that had been placed at traps.
Snowshoe rabbit (Lepus americanus).—Morse (1939:210) in a study of predation on hares and grouse in the period of notable decimation of these two game species in 1935-1936 in the Cloquet Valley State Forest, in St. Louis County, Minnesota, found that "weasel predation on hares appeared to be of very low incidence or altogether lacking."