Nutrient reserves of lesser scaup during spring migration in the Mississippi Flyway: a test of the spring condition hypothesis
The continental scaup population (lesser [Aythya affinis] and greater scaup [A. marila] combined) has declined markedly during the past 20 years, and has remained below the population goal of the North American Waterfowl Management Plan since 1985. One hypothesis explaining the scaup population decl...
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LSU Digital Commons
2002
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| Online Access: | https://digitalcommons.lsu.edu/gradschool_theses/3191 https://doi.org/10.31390/gradschool_theses.3191 https://digitalcommons.lsu.edu/context/gradschool_theses/article/4190/viewcontent/uc.pdf |
| Summary: | The continental scaup population (lesser [Aythya affinis] and greater scaup [A. marila] combined) has declined markedly during the past 20 years, and has remained below the population goal of the North American Waterfowl Management Plan since 1985. One hypothesis explaining the scaup population decline states that reproductive success has decreased because females presently are arriving on breeding areas in poorer condition than that historically (Spring Condition Hypothesis [SCH]). I tested the SCH by comparing fresh body masses (FBMs) and nutrient reserves (lipid, protein, and mineral) of lesser scaup at 4 locations (Louisiana, Illinois, Minnesota, and Manitoba) in the Mississippi Flyway between decades of the 1980s and 2000s. I found that mean FBMs of females were 58.5 g and 58.9 g lower in the 2000s than were those in the 1980s in northwestern Minnesota and near Erickson, Manitoba, respectively; mean FBMs of males similarly were 40.7 g lower in Minnesota. Mean lipid reserves of females in the 2000s were 28.8 g lower than those in the 1980s in northwestern Minnesota and 27.8 g lower near Erickson, Manitoba. Mean mineral reserves of females in the 2000s were 3.2 g lower than those in the 1980s near Erickson, Manitoba. Consequently, females arriving to breed near Erickson, Manitoba in the 2000s had accumulated lipid reserves for 4.1 fewer eggs and mineral reserves for 1 fewer egg than had those arriving to breed in the 1980s. Accordingly, my results clearly are consistent with predictions of the SCH and indicate that there has been a long-term decline in female body condition, reflected by declines in FBMs, lipids and mineral reserves, which could significantly reduce reproductive success. |
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