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Document Type

Thesis - University Access Only

Award Date

2005

Degree Name

Master of Science (MS)

Department

Wildlife and Fisheries Science

First Advisor

Steven R. Chipps

Keywords

lesser scaup, migration, south dakota, food habits, diet

Abstract

The decline of the continental lesser scaup (Aythya affinis) population has become an important conservation issue among waterfowl biologists. Several hypotheses have been proposed to explain why the population is declining including over- harvest, contaminants (mercury, selenium, lead, etc.), changing prey availability and wetland degradation. The objectives of this study were to: (1) determine wetland attributes associated with lesser scaup use in eastern South Dakota, (2) quantify the diets of lesser scaup, (3) evaluate diet overlap between lesser scaup and natives fishes and (4) quantify body composition of migrating lesser scaup. Twenty-nine semi-permanent wetlands located on the Prairie Coteau were sampled for macroinvertebrates in 2004. Lesser scaup were collected over the 2003 and 2004 spring migration periods throughout eastern South Dakota for diet composition and body condition analyses. Lesser scaup were also collected from Highway 81/Twin Lakes, Kingsbury County in 2004 and were used in conjunction with fishes collected at the same time to determine diet overlap between lesser scaup and fishes. Since the mid-1990s, wetlands throughout eastern South Dakota have increased in surface area and water depth. Lesser scaup have been found to frequent wetlands that are relatively large, are stable in area from year to year and have relatively high amphipod densities, a preferred prey item of lesser scaup. However, increased water levels have also resulted in increased fish abundance. Increased fish abundance may affect prey availability for lesser scaup. In this study the fish species with the highest values of diet overlap with scaup were: black bullhead (Ameiurus melas) and yellow perch (Perca flavescens). Amphipods were consistently found in diets of lesser scaup, although they generally represented a low proportion of total energetic contribution. In earlier studies (1980s), the frequency of occurrence of amphipods in scaup diets was noted at 51% (Afton et al. 1991). In this study (2000s), amphipods were found in 33% of scaup diets. Conversely, chironomids were consumed by 25% of scaup collected in the 1980s, while in the 2000s the frequency of occurrence was 35%. Mean body mass of female lesser scaup decreased from 2003 to 2004 (727 g and 701 g, respectively), but body mass of male scaup was statistically similar in 2003 and 2004 (787 g and 746 g, respectively). The body condition of lesser scaup in eastern South Dakota was similar to that reported for Minnesota birds collected by Anteau and Afton (2004). By the time scaup reach South Dakota in early spring, they weigh appreciably less than birds collected at more southern latitudes. The presence of amphipods in scaup diets suggests that amphipods are present in many of the wetlands used by scaup. However, the relatively low frequency of occurrence (about 33% of scaup) combined with the observation that amphipods generally represent a low proportion of total diet composition, implies that amphipod use by scaup may be constrained in early spring. Increased fish abundance, reduced occurrence of amphipods in the diets, increased use of chironomids, and relatively low body mass and lipid content of birds collected in South Dakota are consistent with the spring condition hypothesis proposed by Afton and Anderson (2001). Body mass and lipid content appear to decrease as scaup migrate to northern breeding grounds in spring, and this may have important implications for annual reproduction and population growth of the continental scaup population.

Library of Congress Subject Headings

Lesser scaup -- Food -- South Dakota
Lesser scaup -- South Dakota -- Physiology
Lesser scaup -- Migration -- South Dakota
Body composition
Wetlands -- South Dakota

Description

Includes bibliographical references (page 65-67)

Format

application/pdf

Number of Pages

88

Publisher

South Dakota State University

Rights

Copyright © 2005 Kimberly A. Strand. All rights reserved.

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