existed, the nests were either isolated by distance or visually 

 by intervening terrain and/or vegetation. Table 39 presents the 

 frequency of multiple nesting on islands for 1977, 1978, and 1979 

 For the last 3 years, 50% of the islands used as nest sites had 

 only one nest (range 48-52%) . These islands only accounted for 

 19.8% of the total nests. In 1979, 49.4% of the nests were 

 associated with islands which had between 2 and 5 nests. 



Table 38. Vegetation types of nest site islands. 



Cover Types No. Island/Percent No. Nests/Percent 



Gravel 7 11 



Willow 41 66 87 57 



Cottonwood-willow 10 16 39 26 



Cottonwood-meadow 



Equisteum 3 5 11 



62 152 



Data on island availability and utilization are presented in 

 Tables 40 and 41. In 1979, 62 (41%) of the 150 islands available 

 were used as nest sites. This was up from the 50 (33%) islands 

 used in 1978. Utilization of islands by river section ranged from 

 31% for the PN ferry to Robinson Bridge section, to 69% for Fort 

 Benton to Loma . The average number of islands per mile was 0.93. 

 The corresponding average number of nests per mile was 0.68 in 

 1977, 0.78 in 1978, and 0.93 in 1979. 



The sections of river from Carter to Loma had an above-average 

 number of nests per mile, while other sections were below average. 

 The availability of islands would account for some of this dif- 

 ference by sections, but there appears to be a clear preference 

 for certain river sections. 



80 



