Graduate Thesis Or Dissertation
 

Productivity and nesting habitat of Great Basin Canada geese : Umatilla National Wildlife Refuge

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  • Great Basin Canada goose (Branta canadensis moffitti) productivity and nesting habitat utilization were studied on the Columbia River within the boundaries of the Umatilla National Wildlife Refuge during the springs of 1974 and 1975. Five islands, BL-1, BL-2, SD-1, SD-2, and Telegraph Island (TI), contained 88 percent of the nesting population during both field seasons. Densities on these islands ranged from 0.4/acre (BL-1) to 10.9.acre (TI). Mean clutch size (5.9 and 5.8) did not differ significantly between years, but nesting success decreased from 82 percent in 1974 to 61 percent in 1975. Comparison of the 1974 and 1975 production information of the Umatilla population with other studies of B. c. moffitti from the Pacific Northwest indicated that the nest initiation date (early March), hatching success (89 percent) and percent successful nests (71.4 percent) all corresponded Four factors were suspected of decreasing nest success: 1) increased public utilization of the nesting islands; 2) earlier nest visitations; 3) more frequent visits to nest sites; and 4) freezing temperatures during the egg-laying period in 1975. Statistical treatment of the vegetational measurements on the major nesting islands revealed significant differences between nest sites and transects. A Pearson correlation test of percent forb cover, percent canopy cover, percent bunchgrass cover, and number of dead shrubs had a highly significant (P<0.001, df = 181) negative correlation between percent canopy cover and the other three variables at nest sites but not along the island transects. Linear regression indicated a significant relationship between distance and height of the nearest shrub from the nest site. The nesting B. c. moffitti on the Umatilla NWR did not appear to exhibit the nest site selection preferences attributed to most populations of this sub-species. Vegetation that provided protection from the persistent, strong winds and provided visual isolation for the nest sites was selected by the resident B. c. moffitti.
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