Large, high-relief islands used for nesting in the downstream sections 

 commonly had an extensive vegetative cover. These islands were usually ice- 

 free at the start of the nesting season. Open bars and low-relief islands were 

 also used for nest sites in the upstream sections (figure 10) where they 

 had been largely ice-free before nesting began or melted open during the 

 early stages of nesting. Ice cover on islands in the downstream sections 

 apparently did not induce geese to nest later (an observation based on hatch- 

 ing times of those nests) but did induce them to build their nests on island 

 interiors where ice cover was light or absent. The tendency of ice flows 

 moving downstream to flow past high-relief islands is illustrated in figure 11. 

 These islands, which were mostly free from ice-rouging and flooding (see 

 table 9), were used to a lesser degree in the upstream sections. In 1975 and 

 1976, the average M.C.R.'s for goose nests in study areas upstream from 

 Miles City were 18.5 and 16.5, respectively, compared with 14.4 and 14.0, 

 respectively, in study areas below Miles City. 



TABLE 9. Mean cover ratings from goose nest sites on the lower Yellowstone 



River, 1975 and 1976. 



NOTE: Higher mean cover ratings indicate less dense cover around the 



nest. 



Goose nests were frequently built on or 

 in table 10. The logs often afforded the on 

 otherwise sparsely-vegetated sites. Of the 

 which were constructed on or near driftwood 

 respectively, occurred in the study areas up 

 years, approximately 96 percent of the nests 

 islands. Peninsulas, heron rookeries, and c 

 goose nesting areas. Over 95 percent of the 

 on a fine substrate--one composed primarily 

 Fine substrates probably provide better insu 

 where all other considerations seemed favora 

 of a fine substrate was sufficient to discou 

 was observed only on some small islands whic 

 for nesting in the upstream study sections. 



near driftwood logs, as shown 

 ly nesting cover available on 

 nests surveyed in 1975 and 1976 

 logs, 79 percent and 95 percent, 

 stream from Miles City. In both 



surveyed were constructed on 

 liffs were less important as 

 nests surveyed were constructed 

 of sand or smaller particles, 

 lation for the clutch. Even 

 ble for nest construction, lack 

 rage nest construction. Such lack 

 h might otherwise have been used 



33 



