. The Canadian field-naturalist. Natural history; Sciences naturelles. ground counts. 1987- 1988- 1989- 1990- 1991- 1995- 1996- 1997 89 90 91 92 Year 96 97 98 Figure 5. The estimated percentage of total Snow Goose-days on the Fraser River delta spent on agricultural tields during the "autumn" and "spring" seasons. Source: 1987-1992, Boyd (1995); 1995-1998, Canadian Wildlife Ser\ice et al. (1999*). tSpring use in 1995-1997 is likely underestimated because surveys ended several weeks before spring migration (departure). parts of the Fraser Delta was contributing to a reversal
. The Canadian field-naturalist. Natural history; Sciences naturelles. ground counts. 1987- 1988- 1989- 1990- 1991- 1995- 1996- 1997 89 90 91 92 Year 96 97 98 Figure 5. The estimated percentage of total Snow Goose-days on the Fraser River delta spent on agricultural tields during the "autumn" and "spring" seasons. Source: 1987-1992, Boyd (1995); 1995-1998, Canadian Wildlife Ser\ice et al. (1999*). tSpring use in 1995-1997 is likely underestimated because surveys ended several weeks before spring migration (departure). parts of the Fraser Delta was contributing to a reversal in marsh succession. Boyd (1995) also speculated that the reason that production in the brackish marshes of the Skagit River delta was even lower (, 10%) than the 15% figure reported for the Fraser River delta was because the Skagit River delta supported about twice as many goose-days as did the Fraser River delta dur- ing 1987-1992. Further, there is some concern that in recent years a greater proportion of the Wrangel Island population has been overwintering on the Fraser and Skagit deltas (Pacific Fly way Council 2006*). If Snow Geese were excluded from all agricultural fields, including the sanctuary on Reifel and Westham islands, the segment would likely decline to a habitat- limited maximum size of -15 ()00-20 000 birds. Al- though that scenario may be unrealistic, it is possible that changing land-uses and agricultural practices throughout the Wrangel Island population's winter range, in addition to changes in farmers' tolerance of Snow Geese in their fields, could direct even more for- aging pressure onto brackish marshes. Regardless of farm-field availability, brackish marshes will always be vital for Snow Geese because during extended periods of freezing, the marshes are used exclusively (Boyd 1995). Use of marshes during cold weather likely reflects difficulties geese experience in obtaining food from the frozen or snow-covered soil of agricul- tural fields. Sno
Size: 1486px × 1681px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, books, booksubjectnaturalhistory
