Comments on the Taxonomy and Geographic Distribution of North American Microtines

by E. Raymond Hall; E. Lendell Cockrum

Microtus oeconomus amakensis (Murie)

1930. Microtus amakensis Murie, Jour. Mamm., 11:74, February 11, type from Amak Island, Bering Sea, Alaska.

When Murie (Jour. Mamm., 11:75, February 11, 1930) named the meadow mouse from Amak Island, Alaska, as amakensis, he arranged it as a separate species. One of us (Hall) and K. R. Kelson examined the type and topotypes of amakensis in the Biological Surveys collection in the U. S. National Museum and compared them with series of Microtus oeconomus operarius, M. o. sitkensis, M. o. elymocetes, M. o. yakutatensis, and M. o. kadiacensis. Among the specimens examined of the latter subspecies were 17 from Izambek Bay, Kodiak Peninsula, on the mainland opposite Amak Island, the type locality of amakensis. The characters given by Murie (op. cit.) serve to separate amakensis from closely related neighboring kinds of meadow mice, but are of the degree and kind that, in this group of meadow mice, separate subspecies rather than species. Although actual intergrades are lacking, the animals from Amak Island are considered to be only subspecifically distinct and to belong to the oeconomus complex. The name Microtus oeconomus amakensis is applied to them.

Microtus longicaudus mordax (Merriam)

1891. Arvicola (Mynomes) mordax Merriam, N. Amer. Fauna, 5:61, July 30, type from Sawtooth (= Alturas) Lake, 7200 ft., east base of Sawtooth Mountains, Blaine County, Idaho.

1938. Microtus longicaudus mordax, Goldman, Jour. Mamm., 19:491, November 14.

Dalquest (Univ. Kansas Publ., Mus. Nat. Hist., 2:353, April 9, 1948) assigned all the meadow mice of the species Microtus longicaudus from approximately the eastern half of Washington State to Microtus longicaudus halli Hayman and Holt and, in doing so, excluded the subspecies Microtus longicaudus mordax from that state. This assignment of specimens in Washington had the effect of separating the geographic range of M. l. mordax into two parts. One part was in south-central British Columbia and the other part was mainly in the Rocky Mountain region of the United States. Hall and Kelson examined specimens in the Biological Surveys collection in the U. S. National Museum in an attempt to determine more precisely the ranges of the subspecies in southern Canada, Washington, and Idaho.

Microtus longicaudus angustus [= M. l. halli] was described by one of us (Hall, Univ. California Publ. Zool., 37:13, April 10, 1931) as differing from mordax in narrower braincase, higher skull near the anterior end of the frontals, darker coloration, and seemingly smaller size. After examining the material in the U. S. National Museum no reason is seen at the present time to amend this characterization, except to add that some specimens of M. l. mordax are as dark as seasonably comparable specimens of M. l. halli.

Examination of specimens of Microtus longicaudus from Washington east of the Cascade Range (those from the Blue Mountain area excepted) discloses that the skulls do not differ essentially from those of topotypes of M. l. mordax, but do differ, as outlined above, from near-topotypes of M. l. halli. There is considerable variation in color among the Washington-taken specimens of Microtus longicaudus. Animals from the eastern flanks of the Cascades average darker than those taken, north of the Snake River, still farther east in Washington. Possibly Dalquest (op. cit.) relied mainly upon this darker color in assigning the specimens from eastern Washington to M. l. halli. Relying principally upon cranial characters, we conclude that most of the specimens are better referred to M. l. mordax and that M. l. halli is restricted, in Washington, to the Blue Mountains.

Specimens examined of Microtus longicaudus mordax.—Total, 74, all in the Biological Surveys Collection, distributed as follows: Washington: Okanogan County: mouth of Holmar Creek, W Fork Paysaten River, 4700 ft., 1; Conconully, 3; Twisp, 1; Omak Lake, 1200 ft., 3. Stevens County: 5 mi. N Colville, 1. Pend Oreille County: 9 mi. N Metalina, 2600 ft., 1; Sullivan Lake, 3000 ft., 3. Chelan County: Sethekin, 1079 ft., 3; head of Lake Chelan, 900 ft., 12; Hart Lake, Railroad Creek, 3900 ft., 1; Entiat, 20 mi from mouth of Entiat River, 1680 ft., 13; Wenatchee, 4. Douglas County: Waterville, 1. Jefferson County: Cleveland, 2. Kittitas County: 2 mi. S Blewett Pass, 3000 ft., 6: Ellensburg, 1500 ft., 4. Whitman County: Colfax, 2. Yakima County: McAllister Meadows, Tieton River, 3000 ft., 3; Gotchen Cr., 5500 ft., near Sava Spring, Mt. Adams, 2. Klickitat County: 8 mi. S Glenwood, base Mt. Adams, 2. Asotin County: Anatone, 3300 ft., 4; Bly, 1000 ft., 2.