Breeding Period 



Geese Present. Breeding populations of geese in the study area during 

 this period could not be accurately counted. Based on the total number of 

 pairs and singles observed on aerial censuses (Hanson and Browning 1959), 

 the breeding population was estimated to be 484 breeding pairs on the first 

 1975 census, 433 on the second 1975 census, and 404 on the 1976 census. 

 However, many pairs observed from the air were found by ground observation 

 to be nonbreeding birds only defending a territory. Breeding pair counts 

 conducted in early May when hens were incubating were based on observations 

 of territorial males defending territories in addition to some late-nesting 

 and renesting pairs. The omission of some breeding pairs from the aerial 

 censuses by overlooking some solitary males and the erroneous inclusion of 

 some nonbreeding pairs probably negate each other to some degree. Therefore, 

 a rough estimate of the size of the breeding population of geese in the study 

 area at 400 to 450 pairs may reasonably be made. 



Hanson (1965) reported the use of egg measurements in delineating possible 

 breeding areas of giant Canada geese. He believed that the geese breeding 

 alonq the Yellowstone River were giant Canada geese. Table 4 shows that, 

 based on egg sizes, approximately 20 to 25 percent of the geese breeding in the 

 study sections on the lower Yellowstone River are giant Canada geese. Other 

 characteristics of giant Canada geese observed among some breeding birds 

 included a white forehead spot, massive bill, large tarsal scutes, light 

 color, and posterior extension of the cheek patches (Hanson 1965). The 

 remaining 75 to 80 percent of the breeders are believed to be members of the 

 Great Basin race or possibly a hybrid of Great Basin and giant Canada geese 

 (Hinz 1974). 



TABLE 4. Racial composition of Canada goose flocks nesting in study sections along the 

 lower Yellowstone River based upon sizes of eggs in completed clutches. 



Section 



Bighorn to Hysham 

 Sanders to Forsyth 

 Hathaway to Miles City 

 Miles City to Sunday Creek 

 Sunday Creek to Terry 

 Fallon to Glendive 



MEANS AND TOTALS 



1975 



B.C. moffiti a B.c. maxima 



57.1 (4) 



75.0 (6) 

 100.0 (13) 



55.5 (5) 



42.9 (3) 



25.0 (2) 

 0.0 (0) 



44.5 (4) 



1976 



B.c. moffiti a B.c. maximal 



79.2 (19) 



33.3 (10) 

 75.0 (3) 

 75.0 (3) 

 84.6 (11) 

 69.2 (9) 



20.8 (5) 



16.7 (2) 

 25.0 (1) 

 25.0 (1) 

 15.4 (2) 



30.8 (4) 



75.7 (28) 24.3 (9) 78.6 (55) 21.4 (15) 



NOTE: All entries are expressed as percentages followed by, in parentheses, 

 number of nests. 



a Clutches with eggs whose lengths averaged 87.0 mm or over. 

 b Clutches with eggs whose lengths averaged under 87.0 mm. 



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