Nutrient Reserves of Lesser Scaup (Aythya Affinis) During Spring Migration in the Mississippi Flyway: A Test of the Spring Condition Hypothesis

Abstract

AяѠѡџюѐѡ.-The continental scaup population (Lesser [Aythya affi nis] and Greater [A. marila] combined) has declined markedly since 1978. One hypothesis for the population decline states that reproductive success has decreased because female scaup are arriving on breeding areas in poorer body condition than they did historically (i.e. spring condition hypothesis). We tested one aspect of that hypothesis by comparing body mass and nutrient reserves (lipid, protein, and mineral) of Lesser Scaup at four locations (Louisiana, Illinois, Minnesota, and Manitoba) between the 1980s and 2000s. We found that mean body mass and lipid and mineral reserves of females were 80.0, 52.5, and 3.0 g higher, respectively, in the 2000s than in the 1980s in Louisiana; similarly, body mass and lipid and mineral reserves of males were 108.8, 72.5, and 2.5 g higher, respectively. In Illinois, mean body mass and lipid reserves of females were 88.6 and 56.5 g higher, respectively, in the 2000s than in the 1980s; similarly, body mass and lipid and mineral reserves of males were 80.6, 76.0, and 2.7 g higher, respectively. Mean body mass of females were 58.5 and 58.9 g lower in the 2000s than in the 1980s in Minnesota and Manitoba, respectively; mean body mass of males, similarly, were 40.7 g lower in Minnesota. Mean lipid reserves of females in the 2000s were 28.8 and 27.8 g lower than those in the 1980s in Minnesota and Manitoba, respectively. Mean mineral reserves of females in the 2000s were 3.2 g lower than those in the 1980s in Manitoba. Consequently, females arriving to breed in Manitoba in the 2000s had accumulated lipid reserves for 4.1 fewer eggs and mineral reserves for 0.8 fewer eggs than those arriving to breed there in the 1980s. Accordingly, our results are consistent with the spring condition hypothesis and suggest that female body condition has declined, as refl ected by decreases in body mass, lipids, and mineral reserves that could cause reductions in reproductive success and ultimately a population decline.

Diets of Lesser Scaup during Spring Migration throughout the Upper-Midwest are Consistent with the Spring Condition Hypothesis

“…Collections, described below, were conducted exactly as in and Anteau and Afton (2004;2006;2008a), allowing for direct comparisons among these studies. Female scaup were collected randomly with a shotgun without the use of decoys to avoid associated biases (Pace and Afton 1999).…”

“…Nutrient reserves acquired during spring migration are important determinants of survival and reproductive success in Lesser Scaup (hereafter scaup), and northern spring stopover areas are important for accumulation of these reserves (Afton 1984;Afton and Ankney 1991;Pace and Afton 1999;Anteau and Afton 2004). The Spring Condition Hypothesis (SCH) states that reproductive success of scaup has declined because females currently are in lower body condition during spring migration than in the past (Afton and Anderson 2001).…”

“…The Spring Condition Hypothesis (SCH) states that reproductive success of scaup has declined because females currently are in lower body condition during spring migration than in the past (Afton and Anderson 2001). Female scaup currently have fewer lipid reserves than did those historically (Anteau and Afton 2004;Anteau and Afton 2008a) and catabolize those lipid reserves as they migrate throughout the upper-Midwest in spring (Anteau 2006). Thus, results from these recent studies are consistent with the "lower body condition" prediction of the SCH.…”

“…The apparent decrease in amphipod densities in the upper-Midwest could lead to a decrease in amphipod consumption by scaup across this large landscape. Accordingly, we investigated scaup diets on northern spring stopover areas in the upper-Midwest because changes in forage quality or availability across a large landscape could have precipitous effects on female body condition and concomitant reproductive success (Anteau 2002;Austin et al 2002;Anteau and Afton 2004, 2006, 2008a.…”

Spatiotemporal distributions of intestinal helminths in female lesser scaupAythya affinisduring spring migration from the upper Midwest, USA

“…Spring migration is an energetically expensive time in the annual cycle of waterfowl, especially for females that must not only replace endogenous resources expended during migration but also simultaneously develop reserves for subsequent breeding efforts. Therefore, it is important to understand the effects of parasitic infections on female scaup since future recruitment is tied to their condition and reproductive capacity (Anteau & Afton, 2004). Intestinal helminths tend to reduce the condition of their host through direct and indirect means (e.g.…”