Body Mass of Lesser Scaup during Fall and Winter in the Mississippi Flyway

Abstract

The combined continental breeding population of greater and lesser scaup (Aythya marila and A. affinis, respectively) in North America has declined markedly since the mid-1980s (Afton and Anderson 2001). Annual breeding population estimates have been consistently below the North American Waterfowl Management Plan (NAWMP) goal of 6.3 million scaup (United States Fish and Wildlife Service and Canadian Wildlife Service 1986), and the 2005 estimate was 46% below the NAWMP goal and the lowest on record (Wilkins et al. 2005). Afton and Anderson (2001) reported the overall decline in scaup may be driven primarily by reductions in the lesser scaup population. Multiple hypotheses have been posed to address the scaup population decline, which may be influenced by factors operating throughout the annual cycle and range of scaup (Austin et al. 2000, Afton and Anderson 2001). Anteau and Afton (2004) evaluated the spring condition hypothesis and reported nutrient reserves of female lesser scaup at spring stopover areas in the upper Mississippi Flyway and breeding areas in Manitoba, Canada, were lower in 2000 and 2001 than in the 1980s and reported that these nutrient reserves may impact female survival, breeding propensity, and reproductive success. However, body mass dynamics of fall migrating and wintering scaup have not been studied since the 1980s and early 1990s in the Mississippi Flyway, and investigations of body mass and nutrient reserves of lesser scaup are needed throughout the annual cycle and range of the species (Austin et al. 2000). Fall and winter body condition influences survival, physiological and behavioral events, and subsequent reproduction of waterfowl (Dubovsky and Kaminski 1994, Barboza and Jorde 2002). Nutrient reserves acquired from foods consumed on wintering and migrational areas can influence breeding propensity and reproductive performance of geese, some ducks, and other migratory birds (Ankney and MacInnes 1978, Alisauskas and Ankney 1992, Norris 2005), including lesser scaup that use lipids acquired during winter, spring migration, or on breeding areas for clutch formation (Esler et al. 2001). We collected lesser scaup during fall 1999–2000 and winter 2000–2001 from Manitoba, Canada, southward within the Mississippi Flyway to Louisiana, USA. Our objectives were to 1) estimate body mass of lesser scaup and analyze sex-specific variation in mass in relation to location of scaup collection, age, body morphometrics, and date of collection, and 2) compare our contemporary estimates of scaup mass to those from previous studies conducted at similar locations.