beyond the range limit east of the mountains that is 

 depicted in the latest distribution map (Pearson et 

 al. 1997). This species has not yet been reported 

 for Idaho (Shook 1984). 



Diurnal butterflies : Butterflies and skippers were 

 collected only on 29 and 30 July in an effort to 

 begin a list of species associated with the sandhills 

 (Appendix 9). The list is nowhere near complete, 

 and the collecting conducted was not sufficient to 

 identify specific microhabitat associations in the 

 sandhills, if in fact they occur. Most of the species 

 collected associate primarily or exclusively with 

 open grasslands or shrub-steppe habitats (Opler 

 1999); grasses, lupines, stonecrops, and asters are 

 the larval food plants for several species. In the 

 latest published state list (Kohler 1980) 

 Beaverhead County is not listed as a location for 

 four of the species (Satyriumfuliginosum, 

 Icahcia lupini, Oarisma garita, and Hesperia 

 juba). Considerable collecting has been under- 

 taken throughout the state since then, and there 

 now are coimty records for each (W. Kerling and 

 S. Kohler personal communication). However, 

 only limited collecting has been conducted in the 

 Centennial Sandhills, and these may be new 

 records for this specific locality. 



Discussion 



We found a variety of vertebrate and invertebrate 

 species using the Centennial Sandhills during our 

 1 999 inventory. It is likely that a few additional 

 vertebrate species will be discovered in the 

 sandhills when more surveys are undertaken. 



The list of invertebrates is in its infancy; we expect 

 sand obligate species (Rust 1 986) to be identified 

 when additional invertebrate groups are studied. 

 For now, the species of tiger beetles identified 

 represent the only invertebrate group that is 

 probably nearly complete. For all vertebrate and 

 invertebrate species identified, several stand apart 

 as having restricted distributions tied to physical 



featijres or vegetation within the Centennial 

 Sandhills. 



Several mammal species in the Centennial 

 Sandhills have specific habitat requirements, 

 although their microhabitat relationships are not 

 clear. Perhaps of greatest interest are the four 

 manmial species of special concem that are now 

 known to occur in tiie sandhills. Both Pygmy 

 Rabbit and Black-tailed Jackrabbit are associated 

 with moderate or dense stands of sagebrush 

 (MacCracken and Hansen 1982, Katzner and 

 Parker 1997), which provide food for the former 

 species and shelter for both; Black-tailed Jackrab- 

 bit is more abundant in ungrazed habitat where 

 grass cover is greater Currently both species are 

 present in very low number in the sandhills, and 

 this probably is related to the limited availability of 

 preferred sagebrush habitat. However, low 

 jackrabbit density throughout the Centennial Valley 

 is reflected in their low fi^equency of occurrence in 

 raptor {Buteo) diets (Restani 1 99 1 ), and other 

 factors may be limiting their abundance. In the 

 sandhills. Great Basin Pocket Mouse appears to 

 be restricted to stabilized low dunes, as they were 

 captured only in the East Hills, despite intensive 

 trapping in the West Hills. This partem might be 

 explained by a greater availability of grass and 

 forb seed (Lesica and Cooper 1999) and better 

 burrow stability afforded by more mature sage- 

 brush. Preble's Shrew, unlike the pocket mouse, 

 appears to be more widespread at low density 

 (assuming the unidentified shrews indicated in 

 Table 2 were this species) and not tied to any 

 particular succession stage or physionomic class, 

 so long as sagebrush cover is present. For both 

 species, additional systematic trapping to define 

 distributions and microhabitat associations is 

 desirable. 



Of the other small mammals. Least Chipmunk and 

 Northern Pocket Gopher are found where tiiere is 

 significant topographical relief in the sandhills, 

 associated with dune slopes and crests regardless 

 of the succession stage (early to late serai). 

 However, pocket gopher activity is most evident in 



16 



