Remarks on Reported Hybrid Ground Squirrels, Citellus

Three hybrid short-tailed ground squirrels have been reported from Western United States. The first was identified as a cross between Citellus annatus and Citellus beldingi (Davis, W. B., the recent mammals of idaho, Caxton Printers, Caldwell, Idaho, 1939: 169). The other two were identified as … “hybrids or may be intergrades” … between Citellus armatus and Citellus richardsoni (Hall, Amer. Midl. Nat., 29: 378, 1943). The studies of Durrant and Hansen (Systematic Zool., 3: 82–85, 1954) on competition between species of short-tailed ground squirrels (Subgenus Citellus ) show that animals of different species never hybridize. Moreover, at the zone of contact between colonies of any two species, the competition is extreme; the burrows and feeding areas of the animals of one species being in some instances but a few feet from those of the other species. I have collected a number of specimens from areas where the ranges of C. armatus overlap those of C. richardsoni and C. beldingi and have found no indication of interbreeding. In addition, I studied several hundred museum specimens of these species and found no indications of interbreeding. This prompted me to re-study the “supposed” hybrids that had been previously reported. Plate 1 X-ray photograph of the dentary bones and extra incisor of a varying lemming that died when 69 days old. I thank Dr. S. D. Durrant, Museum of Zoology, University of Utah, Salt Lake City, Utah, for his supervision and suggestions during the course of this study, and for allowing me to examine the specimens in the University of Utah collection.I also thank Dr. Seth B. Benson, Museum of Vertebrate Zoology, University of California, Berkeley, California, for examining the field notes and museum records pertaining to the specimens suspected to be hybrids, and …