Determination of utilization rates for key browse species is important in big-game management. Graduate stu- 

 dents of the Utah Cooperative Wildlife Research Unit determining the utilization rate for bitterbrush on the Cache 

 National Forest, Utah. (Photo by J. B. Low) 



North American Small Mammal Census, are reli- 

 able even for trend indications. A Denver Center 

 researcher has reported a high degree of correla- 

 tion between white-footed mouse populations de- 

 termined from grid live-trapping and subsequent 

 catches in snap traps along a transect bisecting the 

 grid area. The correlation of .964 suggest the pos- 

 sibility that white-footed mouse populations may 

 be approximated from snap-trap data by using a 

 regression of populations per unit area on snap- 

 trap catches. 



Inventory of pocket gopher popuhitiottsi. — 

 Counting fresh mounds thrown up by pocket 

 gophers over a 48-hour period on sample units 

 shows promise as a census method for pocket 

 gophers. The study carried out coojieratively by 

 the Denver Center and Colorado Agricultural Ex- 

 periment Station on Black Mesa in Colorado has 

 shown a correlation of .80 (significant at the 1-per- 



cent level) between fresh mounds in late summer 

 and gopher numbers as revealed by subsequent 

 trapouts. If the correlation holds for such vari- 

 ables as vegetative types and density or soil mois- 

 ture, it will become a most welcome technique for 

 range managers as well as biologists. 



Factors affecting snuiU-7v animal numbers being 

 studied. — After 6 years of small-mammal trapping 

 in Colorado, an employee at the Denver Center has 

 oliserved high populations of mountain voles fol- 

 lowing a year of good precipitation. Pocket 

 gopher numbers appeared to be up following win- 

 ters with a high accumulated snowfall. Mountain 

 vole numbers were highest where herbaceous 

 ground cover was thickest, this being ungrazed 

 ])lnts in open giasslands. White-footed mouse 

 poinilations could not be associated with weather, 

 but were found genei-ally to be more numerous on 

 grazed than on ungrazed ai'eas. 



6S9-962 O — 63- 



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