Speciation of the Wandering Shrew

The purpose of this report is to make clear the biological relationships between the shrews of the Sorex vagrans-obscurus "species group." This group as defined by H. H. T. Jackson (1928:101) included the species Sorex vagrans, S. obscurus, S. pacificus, S. yaquinae, and S. durangae. The last mentioned species has been shown (Findley, 1955:617) to belong to another species group. Sorex milleri, also assigned to this group by Jackson (1947:131), seems to have its affinities with the cinereus group as will be explained beyond. The position of the vagrans group in relationship to other members of the genus will be discussed.


Of this group, the species that was named first was Sorex vagrans Baird, 1858. Subsequently many other names were based on members of the group and these names were excellently organized by Jackson in his 1928 revision of the genus. Subsequent students of western mammals, nevertheless, have been puzzled by such problems as the relationship of (1) Sorex vagrans monticola to Sorex obscurus obscurus in the Rocky Mountains, (2) Sorex pacificus, S. yaquinae, and S. obscurus to one another on the Pacific Coast, and (3) S. o. obscurus to S. v. amoenus in California. Few studies have been made of these relationships. Clothier (1950) studied S. v. monticola and S. o. obscurus in western Montana and concluded that the two supposed kinds actually were not separable in that area. Durrant (1952:33) was able to separate the two kinds in Utah as was Hall (1946:119, 122) in Nevada. Other mammalogists who worked within the range of the vagrans-obscurus groups have avoided the problems in one way or another. Recently Rudd (1953) has examined the relationships of S. vagrans to S. ornatus.