18 



squirrels ( Spermophilus armatus and/or S. elegans ) which 

 accounted for nearly 4 6% of the total number of individual 

 prey items identified (Table 2) . In this population of 

 Ferruginous Hawks, birds contributed substantially to 

 nesting season diet accounting for nearly 20% of the 

 identified prey items. 



Vegetation diversity in a 375 m^ plot centered at each 

 of 15 nests from the Centennial Valley to the Frying Pan 

 Basin west of Dillon are presented in Table 3. 



DISCUSSION 

 This study concluded an inventory of the majority of 

 public lands in southwest Montana for nesting Ferruginous 

 Hawks. Even though the surveys were initiated too late to 

 observe hawks early in the nesting season, coupled with the 

 fact that breeding phenology was apparently advanced in 1992 

 (Jim Roscoe, pers. comm.), I documented a considerable 

 number of successfully breeding Ferruginous Hawks during the 

 study. The proportion of successfully reproducing hawks was 

 high (81.5%) with only 5 nests failing during the breeding 

 attempt. This value is slightly higher than the 57.9 and 

 70.6% for 1985 and 1986, respectively, reported by Myers 

 (1987) and substantially higher than that reported for 

 southeastern Montana (25-27.3%) (Ensign 1983). However, 

 caution should be exercised when comparing these nesting 

 success data to those of other studies since I may have 



