Diets of Lesser and Greater Scaup During Autumn and Spring on the Lower Great Lakes

Abstract

We examined diets of lesser scaup (Aythya affinis) and greater scaup (A. marila) during autumn 1999 and spring 2000 at 3 major stopover sites on lakes Erie, Ontario, and St. Clair in southern Ontario, Canada. Overall dietary composition did not differ between sexes in lesser or greater scaup. We also did not detect interspecific or sex‐related differences in average size of zebra mussels (Dreissena polymorpha) consumed by scaup, but both species ate slightly larger zebra mussels during spring, as compared with autumn. Dietary intake of lesser scaup differed between seasons and among stopover sites. Lesser scaup generally ate more zebra mussels during spring and more gastropods and plants during autumn. Lesser scaup at Lake Ontario, Lake Erie, and Lake St. Clair, respectively, consumed more zebra mussels, nonmollusk animal matter (crustaceans and insects), and plant matter than did conspecifics at the other 2 locations. Greater scaup diets differed depending on both season and stopover site. At Lake Ontario greater scaup diets contained more zebra mussels but fewer gastropods during spring as compared with autumn, but there were no seasonal differences in consumption of those 2 food items at Lake Erie. Greater scaup at both Lake Ontario and Lake Erie did not show seasonal differences in consumption of plant matter, but autumn‐staging birds at Lake Erie contained more plant matter than did autumn‐staging birds at Lake Ontario. Interspecific comparisons of dietary intake of scaup staging at lakes Erie and Ontario showed that greater scaup generally ate more gastropods and plant matter than did lesser scaup, whereas lesser scaup consumed more zebra mussels than did greater scaup. Overall, our study showed that zebra mussels, gastropods, and submerged aquatic plants all currently are important foods during both autumn and spring for lesser and greater scaup staging on the lower Great Lakes (LGL). Consumption of zebra mussels by scaup is of particular concern because of the hypothesized link between scaup foraging ecology, zebra mussels, and elevated selenium burdens documented recently in scaup staging on the LGL. Thus, our findings that both scaup species generally ate more and larger zebra mussels during spring illustrates the need for further investigation into contaminant acquisition and burdens in wintering, staging, and breeding scaup, particularly those using, or originating from, the LGL region.

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

“…J. Anteau, unpubl. data); thus, when at very high densities, as reported for these particular areas, bivalves and gastropods apparently can be relatively profitable foods (Anteau 2002(Anteau , 2006Badzinski and Petrie 2006).…”

“…Our results are consistent with the prediction that bivalve and gastropod consumption by scaup in the upperMidwest is a result of lack of availability of other preferred foods (Anteau and Afton 2006) because bivalve and gastropod consumption were generally low, except NWMN in 2000-2001 where amphipod consumption was low. In contrast, scaup primarily consume bivalves and gastropods during spring on the Lower Great Lakes and at Pool 19 of the Mississippi River (Badzinski and Petrie 2006;M. J. Anteau, unpubl.…”

Patterns of prey use by lesser scaup Aythya affinis (Aves) and diet overlap with fishes during spring migration

“…The use of alternative prey, however, appears to vary appreciably among locations during annual spring migration. In areas near the Great Lakes, lesser scaup relied heavily on zebra mussels Dreissena polymorpha (Pallas) during spring migration (Badzinski & Petrie, 2006). Fortunately, this invasive species was absent from South Dakota and was not present in scaup diets.…”

Historical and Contemporary Characteristics and Waterfowl Use of Illinois River Valley Wetlands

“…Compositional analysis transforms proportional dependent variables to log-ratios and accounts for this lack of independence (Aebischer et al 1993), but our data set contained many zeros, and this approach may have lead to severely inflated Type I error rates (Bingham and Brennan 2004;Badzinski and Petrie 2006). Examination of residual plots indicated our errors were not multivariate-normal distributed and arcsine square-root transforming the data did not significantly improve error distributions and complicated interpretability.…”

“…Examination of residual plots indicated our errors were not multivariate-normal distributed and arcsine square-root transforming the data did not significantly improve error distributions and complicated interpretability. Therefore, we selected an analytical approach similar to that of wildlife food-habits studies (Afton et al 1991;Ross et al 2005;Badzinski and Petrie 2006) and analyzed change in wetland habitat composition using multivariate analysis of variance (MANOVA) with simple proportions as the dependent variable. We acknowledge deviations from statistical assumptions, but consider our tests appropriate because parametric multivariate analyses are considered robust to many violations of assumptions of linear models (Johnson 1995).…”