Populations of deer mice (Peromyscus maniculatus) 

 increased irregularly from 1976 to 1983, declined abruptly in 

 1984, and slowly increased through 1986 (Figure 5.10). 

 Microtine rodent (Lemmiscus curtatus and Microtus spp . ) 

 populations experienced 3 irruptions during 1976-1987. 

 Populations were at peak levels from summer 1978 through 



1982 through autumn 1983. Another 



summer 1986. No trapping was 



field observations indicated that 



in 1986 continued through autumn 



autumn 1979 and from summer 

 irruption started during 

 conducted during 1987, but 

 the irruption that started 



1987 and was at least as great as previous highs 



180 

 16(H 

 140 

 120- 

 g 100- 





80 -I 

 60 

 40- 

 20- 

 



o Deer Mice 



-• Microtines 



A 



/ \ 



ft 



/ \ y 



/ \ 



/ \ / . 



i 



/ 



-<i 



v-* 



/ 



-l 1 T 1*^ 1 1 T I 1 



1976 1978 1980 1982 1984 1986 



Year 



Figure 5.10. 



Number of individual deer mice and microtines 

 captured on a live-trap grid on the Missouri 

 River Breaks study area during summers 1976- 

 1986. Dotted line for microtines in 1987 

 indicates estimated numbers. 



White-tailed jackrabbit (Lepus townsendii) populations 

 increased from 1976 through 1983, declined sharply by 1984 and 

 remained low through 1986 (Figure 5.11). Numbers of 

 cottontail rabbits (Sylvilagus nuttallii) observed during the 

 surveys (Fig. 5.11) probably did not represent cottontail 

 populations accurately because the routes were designed 

 primarily for jackrabbits and included little good cottontail 

 habitat. Notes from aerial radio relocation flights for deer 



141 



