1975. This lower discharge may have allowed greater accessibility of the 

 nesting islands to predators due to reduced width and depth of the channels 

 separating the islands from the main bank. In 1975, discharge of the 

 Yellowstone at Miles City was lower around the median date of initiation than 

 in 1976 but shortly thereafter increased and nest flooding resulted. Had 

 this increase and subsequent flooding not occurred, losses of nests to predators 

 during that period may have been greater. The relationship between low flows 

 and nest losses to predation versus high flows and nest losses to flooding is 

 more evident in the study areas near and upstream from Miles City. In the more 

 downstream study sections, the spring changes in discharge in 1975-76 were not 

 believed to appreciably alter channel widths. Also, because many of the 

 islands surveyed for nests in the Sunday Creek-to-Terry reach and Fallon-to- 

 Glendive section occur midstream with sizable channels on both sides, the 

 ability of predators to reach them may be limited. 



Egg success in successful nests in both years was approximately 86 percent 

 (appendix E), similar to that reported by Geis (1956) in the Flathead Valley 

 of Montana, by Steel et al . (1957) at Gray's Lake in Idaho, and by Martin (1964) 

 at Bear River, Utah. Embryonic deaths in unhatched eggs accounted for 67 

 percent of the unsuccessful eggs from successful nests in 1975. These deaths 

 were attributed to cold weather on days when nest checks were conducted, which 

 sometimes resulted in chilling of eggs. The proportion of embryonic deaths in 

 unhatched eggs was greatly reduced in 1976 over 1975, possibly due to warmer 

 temperatures and/or clearer skies on nest survey days. 



Eggs injected with colored dyes in 1975 were excluded from calculation 

 of nest and egg success because the dyeing process resulted in abnormally 

 high egg mortality in dyed clutches. Of 90 eggs injected in 18 nests, only 

 36 percent hatched. This poor success rate was attributed to embryonic death 

 caused by green dye in toxic concentration, and dyes used at air temperature. 



Brood-Rearing and Flightless Period 



Geese Present . Numbers of geese observed during censuses conducted in 

 this period (figure 4) are believed to be erroneously low due to the inability 

 of the observer in the air to locate geese hidden in dense cover. 



Crops and Forage Utilized . Geese grazed primarily on grasses and forbs 

 at this time of year. Juvenile birds were believed to utilize insects in their 

 diets as do immature grouse (Peterson 1970) and ducks (Chura 1961), but were 

 believed to feed primarily on green forage by three weeks of age, as indicated 

 by Lieff et al. (1970). 



Movement . During the flightless period in 1975, 157 neck bands were 

 applied to geese on the river and on nearby stockponds. Some subsequent 

 observations of these neck-banded birds occurred during the flightless period 

 (appendix D). Movements which occurred between these observations were believed 

 to be similar to those of goslings from nests where clutches were injected 

 with colored dyes. One blue-dyed gosling from a nest near Myers was observed 

 when three to four weeks old in a hayfield across the channel from the island 

 where it hatched. Contrary to Gen's' s (1956) and Caldwell's (1967) observations 



38 



