Comparison of Vocalizations between and within Spermophilus elegans elegans and S. richardsonii

Vocalizations (particularly alarm calls) are important in the function of sciurid societies (Farentinos, 1974; Owings and Leger, 1980; Owings and Virginia, 1978; Sherman, 1977). Because of their importance, they have value for study as systematic characters. Bolles (1980) used vocalizations to differentiate among species Ammospermophilus. Waring (1970) found prairie dog (Cynomys spp.) vocalizations useful for field identification of species. Smith (1978) found that the two species of Tamiasciurus could be distinguished by their chirp calls. Interspecific differences were great enough in vocalizations of Eutamias (Brand, 1976; Miller, 1944; Sheppard, 1965) that sympatric species could be identified by call alone, and Dunford and Davis (1975) differentiated among species of chipmunks by searching recordings for the presence of a trill or a terminal pulse. Vocalizations may be of particular value as systematic characters in the genus Spermophilus because of the morphological similarity of many of the species. Howell (1938) and Hall (1981) recognized four subspecies of Spermophilus richardsonii: S. r. elegans, S. r. aureus, S. r. nevadensis, and S. r. richardsonii. However, chromosomal and morphological evidence (Nadler 1966; Nadler et al., 1971; Robinson and Hoffmann, 1975) indicated that the S. richardsonii complex may consist of two species as proposed by Davis (1939), S. elegans (including S. e. elegans, S. e. aureus, and S. e. nevadensis) and S. richardsonii. Zegers (1984) and Michener and Koeppl (1985) treated S. elegans and S. richardsonii as separate species. Koeppl et al. (1978) noted differences between vocalizations of sympatric, hybridizing populations of S. elegans and S. richardsonii in Montana that would support recognition of two species. Their tests to determine whether calls paralleled systematic relationships were inconclusive; however, chirp calls seemed convergent where species were sympatric whereas churr calls seemed unaffected. My objectives were to determine whether differences in vocalizations noted by Koeppl et al. (1978) in the region of sympatry were maintained in other portions of the range of each species, to quantify those differences, and to determine whether significant geographic variation existed within each species. Geographic vocal variation has been observed for a few species of mammals, including elephant seals (Mirounga angustirostris) (LeBoeuf and Peterson, 1969), cetaceans (Winn et al., 1981), pikas (Ochotona princeps) (Conner, 1982; Somers, 1973), Japanese monkeys (Macaca fuscata) (Green, 1975), and prairie dogs (Cynomys gunnisoni zuniensis) (Slobodchikoff and Coast, 1980). I recorded vocalizations from captive animals obtained from two populations for each of the two species. Twelve Spermophilus elegans elegans (four males and eight females) were trapped 8 km N of Kremmling, Grand County, Colorado, and nine (two males and seven females) were trapped 17 km N of Encampment, Carbon County, Wyoming. The two localities were 170 km apart. Ten Spermophilus richardsonii (four males and six females) were trapped 7 km S of White Sulphur Springs, Meagher County, Montana, and five (three males and two females) were born to field-impregnated females trapped 8 km E of Picture Butte, Alberta, Canada. The Montana and Alberta localities were 400 km apart. Field observations on the context of calls were made for both S. elegans and S. richardsonii. Ground squirrel vocal responses were recorded in the laboratory without stimulus, when prodded, when