Analysis of Pacific Coast Townsend Chipmunks (Rodentia: Sciuridae)

Abstract

Comparison of Eutamias ochrogenys, Eutamias senex, Eutamias siskiyou, and Eutamias townsendii along the Pacific coast of northwestern California and southwestern Oregon was undertaken to re-evaluate some of the distinguishing characters, to examine the validity of described distributions, and to look for the occurrence of intergrades at the described river boundaries between the species. Discriminant function analyses of 296 specimens showed clear differences in the four species, and the three river boundaries separated them with no discernible intergradation. Howell (1929) described the morphology and distribution of five races of Townsend chipmunks, Eutamias (= Tamias of Levenson, 1982) townsen- dii. This was accepted by Johnson (1943), Hall and Kelson (1959), and others. In a systematic revision by Sutton and Nadler (1974), E. t. ochrogenys, E. t. senex and E. t. siskiyou were accorded species status as Eutamias ochrogenys, Eutamias senex and Eutamias siskiyou. This was accepted by Hall (1981). The status of E. t. cooperi and E. t. townsendii was left as described by Howell because we had insufficient numbers upon which to base consideration. Considerable change was made in the distributions of the three new species. Eutamias ochrogenys was found northward from near Bodega, Sonoma Co., California, to the area of the Van Duzen River, Humboldt Co., California. Eutamias senex was found in Humboldt Co. northward from near the Van Duzen River to the Klamath River and eastward to the Cascade and Sierra ranges. Eutamias siskiyou was distributed from the Klamath River in Humboldt Co. northward through Del Norte Co. to th Rogue River in Curry Co., Oregon, and eastward in the Siskiyou and Cascade mountains. Whereas river boundaries do not constitute impenetrable barriers for chipmunks, especially in late summer, 296 animals collected in this coastal area could be assigned to species with confidence. The river boundaries between the specimens were sharp, with no evident intergradation (contra Levenson and Hoffmann, 1984). Three studies at Humboldt State University, Arcata, California, were initiated to test the validity of our classifications and distributions of Townsend chipmunks in northwestern California. Williams (1980) found discrete differences among the three species, with clear geographic and reproductive isolation at the Van Duzen, Klamath, and Rogue rivers and no evidence of hybridization. Douglas Kain (pers. comm.) found that genital bones, cranial characters, and eledtrophoretic data clearly differentiate E. ochrogenys and E. senex, and these species were geographically separated by the Eel River. William Gannon (pers. comm.) made sonograms of alarm calls and found that calls of the three species fall into three clusters