1977-1978, 0.2/km2 (0.5/nii2). The spring and summer estimates are probably the 

 least accurate, due to the wide dispersal of groups and how observability of 

 fawns during these two seasons. These figures compare to minimum density 

 estimates based on 1967 and 1973 MF&G censuses in H.D. 650 of 0. 3/km2(0.7/mi2) 

 and 0.6/km2 (l.S/mi^), respectively. Although some studies have obtained larger 

 pronghorn density estimates than the present study, Knapp (1977) considered a 

 density of 0.2/km^ (O.S/mi^) to be characteristic of a "good" population in the 

 Birney-Decker area of southeastern Montana. 



Seasonal use of habitat categories (vegetation types) and topography types 

 are shown in figures 33 and 34. Grasslands and sagebrush types appeared to have 

 the highest importance yearlong for antelope (figure 33). Sagebrush habitats 

 were most important during winter; grasslands, sagebrush habitats, and agricul- 

 tural land during spring and summer; and grasslands and agricultural land dur- 

 ing the fall. These findings do not differ greatly from results of pronghorn 

 antelope studies in central Montana (Bayless 1969, Cole and Wilkins 1958) and 

 southeastern Montana (Martin 1976). Although vegetation types were recorded 

 for 94% of all sightings, pronghorn antelope were actually observed feeding 

 in only 31% of the sightings. Topography was recorded at 93% of the sighting 

 locations. (See Appendix K for a detailed account of seasonal habitat use.) 



During the winter months, sagebrush habitats (especially big sagebrush) 

 were important to pronghorn antelope, providing 67% of the observations for 

 the first winter (1976-77) and 50% the second winter (1977-78) (figure 33). 

 The majority of feeding pronghorn antelope were also observed in sagebrush 

 habitats during winter. Other studies have documented the importance of sage- 

 brush in the winter diet of pronghorn antelope (Bayless 1969, Cole and Wilkins 

 1958). Pronghorn antelope were also observed feeding in cultivated and stubble 

 fields during the second winter. Pronghorn antelope were most frequently ob- 

 served on rolling topography during both winters, especially during December 

 (figure 34). During January and February of the first winter, use of coulees 

 and hillsides appeared to increase, while during January of the second winter 

 creek bottoms and badlands became more important. Both shifts in winter topo- 

 graphy use were probably responses to worsening winter weather conditions. 

 Pronghorn antelope were frequently observed feeding on rolling terrain; however, 

 broken topography (including creek bottoms, coulees, and badlands) accounted 

 for the majority of feeding observations during both winters. 



As vegetation greened up in spring, pronghorn antelope were observed on 

 a wide variety of habitat types (figure 33). However, the majority of prong- 

 horn antelope appeared in similar frequencies on grasslands (27%), sagebrush 

 habitats (28%), and cultivated fields (25%) during spring 1977. Feeding was 

 observed on grasslands, sagebrush habitats, and in cultivated fields, including 

 fields of sprouting grain. Reflecting habitat use, the topography of the 

 majority (69%) of spring observation locations was rolling or flat (figure 34). 

 Most feeding observations were also on flat to rolling terrain. 



During the summer of 1977, pronghorn antelope were observed most frequently 

 on grasslands (38%) (figure 33). However, sagebrush habitats (22%) and cul- 

 tivated fields (20%) received substantial use also. Use of grasslands appeared 

 to decrease from June to August while use of cultivated lands increased. Ob- 

 servations of feeding pronghorn antelope were most frequent on grasslands dur- 

 ing June and July, and on silver sagebrush/grasslands during August. Rolling 



136 



