DIETS OF SPRING − MIGRATING WATERFOWL IN THE UPPER MISSISSIPPI
RIVER AND GREAT LAKES REGION
by
Arthur Neil Hitchcock, Jr.
B.S., Mississippi State University, 2005
A Thesis Submitted in Partial Fulfillment of the Requirements for the Master of Science Degree
Department of Zoology In the Graduate School Southern Illinois University Carbondale December 2008
THESIS APPROVAL
DIETS OF SPRING − MIGRATING WATERFOWL IN THE UPPER MISSISSIPPI
RIVER AND GREAT LAKES REGION
By
Arthur Neil Hitchcock, Jr.
A Thesis Submitted in Partial
Fulfillment of the Requirements
for the Degree of
Masters of Science
in the field of Zoology
Approved by:
Dr. Michael W. Eichholz, Chair
Dr. Joshua D. Stafford
Dr. Tina Yerkes
Dr. Matt R. Whiles
Graduate School Southern Illinois University Carbondale August 14, 2008
2 AN ABSTRACT OF THE THESIS OF
JAY HITCHCOCK, for the Master of Science degree in ZOOLOGY, presented on AUGUST 14, 2008, at Southern Illinois University Carbondale.
TITLE: DIETS OF SPRING − MIGRATING WATERFOWL IN THE UPPER MISSISSIPPI RIVER AND GREAT LAKES REGION
MAJOR PROFESSOR: Michael W. Eichholz
I evaluated diet and food selection of 5 species of spring-migrating female
waterfowl including 3 dabbling ducks (Blue-winged teal, Anas discors, Mallard, Anas
platyrhynchos, Gadwall, Anas strepera) and 2 diving ducks (Lesser Scaup, Aythya affinis,
and Ring-necked duck, Aythya collaris). Diet was evaluated with regards to the proportion of invertebrates and seeds consumed, and compared to forage availability data
collected in habitats available to them at 6 study locations throughout the Upper
Mississippi River and Great Lakes Region. I found latitude (i.e., stage of migration),
longitude, food availability, and date all influenced the diet of spring migrating
waterfowl, with some factors having a stronger influence than others. I observed
differing diet trends with regard to foraging guild (e.g., dabbling and diving ducks), as
each foraging guild was represented by 1 species that was heavily dependant on
invertebrates (dabbling duck – Blue-winged teal; diving duck – Lesser scaup) and 1
species that was heavily dependant on seeds (dabbling duck – Mallard; diving duck –
Ring-necked duck). The proportion of invertebrate foods in the diet increased throughout
spring for all species of waterfowl, suggesting the importance of invertebrate food
sources during spring staging. Data from this study provides valuable information to
habitat managers and conservationists wishing to improve spring habitat conditions for
migrating waterfowl, which likely influences waterfowl productivity.
i ACKNOWLEDGMENTS
Without the financial support of Ducks Unlimited, Inc. and several private donors,
USFWS (Upper Mississippi River and Great Lakes Joint Venture), Ohio Division of
Wildlife, Wisconsin DNR, Illinois DNR, Bruning Foundation, Christel DeHaan Family
Foundation, Saginaw Bay Wetlands Initiative Network, Herbert H. and Grace Dow
Foundation, Rollin M. Gerstacker Foundation, Waterfowl Research Foundation, Southern
Illinois University Carbondale, and The Ohio State University this research would not
have been possible.
Although he made it quite clear on several occasions that I was not the ‘sharpest
tool in the shed’, I would like to thank my graduate advisor and friend, Dr. Michael
Eichholz for allowing me to conduct this research and for his support, advise, and
expertise throughout my years at SIU. I am greatly indebted to Dr. Joshua Stafford for
his invaluable statistical expertise and for the hours he committed to editing and replying
to thousands of questions and emails. I would also like to thank my other committee
members, Dr. Tina Yerkes and Dr. Matt Whiles for taking interest in my research and
providing editorial comments and professional advice.
My extensive data set would not have been possible without the countless hours
in the field and laboratory of the many technicians that worked for us. Of those, I would
like to personally thank Stephanie, Cassie, Zac, Kristopher, Tim, Nick, Brent, Bryan,
Chris, Devan, John Fulcher, Big John, Sara, Adam, Melissa, and Rick for helping with
duck collection and laboratory analyses of gut contents. Many thanks are due to
collaboraters Rich Schultheis, Jake Straub, Kyle Loper, Dr. Robert Gates, and Dr. John
Colucci for their dedication to the project and timely delivery of data. I have thoroughly
ii enjoyed making new friends and colleagues at SIU, all of which have made my time here more enjoyable.
Thanks to several federal refuges, state wildlife areas, and private landowners for allowing this research to be conducted on their property. Specifically, Cypress Creek
National Wildlife Refuge, Chautauqua National Wildlife Refuge, Horicon National
Wildlife Refuge, Central Gun Club, Winous Point Hunt Club, and Bill and Vivian Young for providing us with housing during our field season. I am greatly appreciative of the logistical and fieldwork help by Aaron Yetter, Chris Hine, Dr. Joshua Stafford, and
Randy Smith of the Illinois Natural History Survey Forbes Biological Station in Havana,
IL.
I am especially indebted to my family for their love and support throughout my life and for supporting me as I follow my dream to be a wildlife/waterfowl biologist. To my wife, Randa, I would have to write another thesis to explain my gratitude and love for you. Your patience and love have upheld me throughout the writing process. No more graduate school – I promise! Just you, me, and Belle. And duck season!
iii TABLE OF CONTENTS
CHAPTER PAGE
ABSTRACT……………………………………………………………………………….i
ACKNOWLEDGMENTS………………………………………………………………...ii
LIST OF TABLES……………………………………………………………………...... vi
LIST OF FIGURES…………………………………………………………………...…..x
GENERAL INTRODUCTION ………………………………………………………...…1
CHAPTER 1 – DIET OF MIGRATING WATERFOWL DURING SPRING IN THE UPPER MISSISSIPPI RIVER AND GREAT LAKES REGION………….…....5
INTRODUCTION……………………………….………………………………………..5 Diet in Relation to Annual Life Cycle of Waterfowl ………...………………….5
STUDY OBJECTIVES …………………………………………………………………...7
METHODS ……………………………………………………………………………….8 Study Site Selection ……………………………………………………………...8 Study Species ………………………………………………………………...…15 Waterfowl Collection ……………………………………………………...……16 Laboratory Analysis …………………………………………………………....17 Statistical Analysis …………………………………………………………..…18
RESULTS ……………………………………………………………………………….20 Summary Statistics ……………………………………………………………..20 MANCOVA results ………………………………………………………….…31 Breeding vs. Non-breeding …………………………………………..…31 Diet ………………………….………………………………………….33 Blue-winged Teal Diets………..………………………………………..33 Mallard Diets ……...... …………………………………………………43 Gadwall Diets ………………………...... ……………………………....50 Lesser Scaup Diets ……...... ………………………………………...…55 Ring-necked Duck Diets ………...... ……………………………………61
DISCUSSION …………………………………………………………………………...65 Temporal and Latitudinal Variation in Spring Diet Within a Species …….....…74 Longitudinal Variation in Spring Diet Within a Species ……………………….76
iv CHAPTER 2 – FOOD SELECTION BY MIGRATING WATERFOWL DURING SPRING IN THE UPPER MISSISSIPPI RIVER AND GREAT LAKES REGION ………………………………………………………………………..80
INTRODUCTION ………………………………………………………………………80 Food Selection ……………………………………………………………….…80
STUDY OBJECTIVES ………………………………………………………………….83
METHODS …………………………………………………………………………..….85 Food Availability ………………………………………………………………85 Laboratory Analysis ……………………………………………………………87 Statistical Analysis ………………………………………………………….….88
RESULTS …………………………………………………………………………...…..89 Availability ……………………………………………….……………………..89 Blue-winged Teal Food Selection ……………………….……………...………89 Mallard Food Selection ………...... …………………………………………..91 Lesser Scaup Food Selection ……………………………………….………..…91 Ring-necked Duck Food Selection ………….....…………………………....….93
DISCUSSION …………………………………………………………………...... ……93 Food Selection ……………………………………………………………….....93 Blue-winged Teal …………………………………………….………...... …94 Mallard ……………………………..………………………….………..…..95 Lesser Scaup …………………...... ……………………..…………....…...97 Ring-necked Duck ……………………………………………….……....…99
CHAPTER 3 − IMPLICATIONS FOR WETLAND MANAGEMENT FOR SPRING − MIGRATING WATERFOWL IN THE UMR/GLR…....……...... ……101
Management Implications ...... 101 Managing Wetlands for Invertebrates During Spring Migration ...... 102 Managing Wetlands for Seeds During Spring Migration ...... 103 Challenges to Providing Habitat for Spring-Migrating Waterfowl ...... 104
LITERATURE CITED …………...... ……………………………………………….105
APPENDICES Waterfowl Diets at Different Study Sites...... …………...…………………………….114
VITA ……...……..……………………………………………………………………..162
v LIST OF TABLES
TABLE PAGE
Table 1.1 Number of ducks collected in the Upper MS River and Great Lakes Region that contained food items during spring 2006 and 2007 (BWTE = blue-winged teal, MALL = mallard, GADW = gadwall, RNDU = ring-necked duck, LESC = lesser scaup, CA = Cache River, IR = Illinois River, WI = Wisconsin, SR =Scioto River, LE = Lake Erie, SB = Saginaw Bay) ...... 21
Table 1.2 Aggregate percent (A) ± standard error and percent occurrence (O) of food items in ducks (BWTE = blue-winged teal, MALL = mallard, GADW = gadwall, LESC = lesser scaup, RNDU = ring-necked duck) collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007…….………...... 21
Table 1.3 Aggregate percent biomass of animal foods consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 1.0% aggregate mass, they were listed as trace (tr.)...... 22
Table 1.4 Aggregate percent biomass of plant foods consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.5% aggregate mass, they were listed as trace (tr.)...... 24
Table 1.5 Aggregate percent biomass of vegetation consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.1% aggregate mass, they were listed as trace (tr.) ...... 26
Table 1.6 Aggregate percent biomass of animal foods consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 1.0% aggregate mass, they were listed as trace (tr.)...... 27
Table 1.7 Aggregate percent biomass of plant foods consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.5% aggregate mass, they were listed as trace (tr.)...... 29
Table 1.8 Aggregate percent biomass of vegetation consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007...... 32
vi Table 1.9 Results from the initial MANCOVA model evaluating the effects of site, species (Sp), date (Jul), habitat (Hab), reproductive status (RS) and year (Yr) on proportions of invertebrates and seeds consumed by 5 species of ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007...... 34
Table 1.10 Date of first and last dabbling duck collected at each study site in 2006 and 2007 ...... 37
Table 1.11 Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), reproductive status (RS), and year (Yr) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006 and 2007...... 38
Table 1.12 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), reproductive status (RS), year (Yr) and transect by year (Tran*Yr) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006 and 2007…………...... 40
Table 1.13 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and reproductive status (RS) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006 ………...... 41
Table 1.14 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and reproductive status (RS) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2007 ……...... …...... 42
Table 1.15 Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), reproductive status (RS), and year (Yr) on proportions of invertebrates and seeds consumed by mallards in the Upper MS River and Great Lakes Region during spring 2006 and 2007…...... 46
Table 1.16 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), reproductive status (RS), year (Yr) and transect by year (Tran*Yr) on proportions of invertebrates and seeds consumed by mallards in the Upper MS River and Great Lakes Region during spring 2006 and 2007 ……...... ……………...... 48
vii Table 1.17 Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006 and 2007………...... 51
Table 1.18 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), year (Yr) and transect by year (Tran*Yr) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006 and 2007 ...……...... ………………...... 53
Table 1.19 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), and habitat (Hab) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006 ………...... 54
Table 1.20 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), and habitat (Hab) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2007 ………...... 56
Table 1.21 Date of first and last diving duck collected at each study site in 2006 and 2007 ...... 59
Table 1.22 Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by lesser scaup in the Upper MS River and Great Lakes Region during spring 2006 and 2007…...... 60
Table 1.23 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by lesser scaup in the Upper MS River and Great Lakes Region during spring 2006 and 2007 ...... 63
Table 1.24 Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by ring-necked ducks in the Upper MS River and Great Lakes Region during spring 2006 and 2007…...... 66
Table 1.25 Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by ring-necked ducks in the Upper MS River and Great Lakes Region during spring 2006 and 2007….……...... 68
viii Table 2.1 Mean food availability (kg/ha) and standard error (SE) of seeds and invertebrates found in shallow (for dabbling ducks) and deep (for diving ducks) habitats during spring 2006………..…………………...…90
Table 2.2 Results of selection analyses for ducks collected at study sites in the Upper MS River and Great Lakes Region (CA = Cache River, IR = Illinois River, WI = Wisconsin, SR = Scioto River, LE = Lake Erie, and SB = Saginaw Bay) during spring 2006. An “I” indicates selection of invertebrates, “=” indicates consumption in proportion to availability, and “S” indicates selection of seeds ….……………..…...…92
Table 2.3 Mean percentage of food items and standard error (SE) in diet of dabbling ducks at study sites in the Upper MS River and Great Lakes Region during spring 2006 ……...... ………………………...……96
Table 2.4 Mean percentage of food items and standard error (SE) in diet of diving ducks at study sites in the Upper MS River and Great Lakes Region during spring 2006 ………...... ……………………..…………...98
ix LIST OF FIGURES
FIGURE PAGE
Figure 1.1 Location of the Upper MS River and Great Lakes Region with respect to wintering and breeding grounds of ducks migrating through the Upper MS River and Great Lakes Region (image taken from United States Fish and Wildlife Service 2008) ...... 9
Figure 1.2 Location of study sites in the Upper MS River and Great Lakes Region (image provided by Jake Straub, The Ohio State University) ...... 10
Figure 1.3 Percent of seeds and invertebrates in the diet of 6 species (BWTE = blue-winged teal, MALL = mallard, GADW = gadwall, LESC = lesser scaup, RNDU = ring-necked duck) collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means...... 35
Figure 1.4 Percent of seeds and invertebrates consumed by blue-winged teal at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ……………………..…….....39
Figure 1.5 Percent of seeds and invertebrates consumed by blue-winged teal at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………44
Figure 1.6 Percent of seeds and invertebrates consumed by blue-winged teal at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ……45
Figure 1.7 Percent of seeds and invertebrates consumed by mallards at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... …………………………………....47
x Figure 1.8 Percent of seeds and invertebrates consumed by mallards at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ……49
Figure 1.9 Percent of seeds, vegetation, and invertebrates consumed by gadwalls at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………..……………...... 52
Figure 1.10 Percent of seeds, vegetation, and invertebrates consumed by gadwalls at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………57
Figure 1.11 Percent of seeds, vegetation, and invertebrates consumed by gadwalls at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………58
Figure 1.12 Percent of seeds and invertebrates consumed by lesser scaup at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………………………...... 62
Figure 1.13 Percent of seeds and invertebrates consumed by lesser scaup at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means …....……64
Figure 1.14 Percent of seeds and invertebrates consumed by ring-necked ducks at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ...... ………………………..…..67
Figure 1.15 Percent of seeds and invertebrates consumed by ring-necked ducks at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares mean ± standard error). Different letters indicate significantly different means ....………69
xi
GENERAL INTRODUCTION
Diets of most organisms are primarily determined by what foods are available to them, but also vary among species of closely related organisms, stage of growth, reproductive status, and stage of annual cycle; the latter 3 are likely most influenced by physiological changes in nutritional demand (Sedinger 1992). For example, diets of many animals coincide with changes in forage abundance and quality (Kennish 1996), and small changes in forage quality may influence fitness. Reindeer (Rangifer tarandus
L.) in Alaska that fed in high-quality habitats (i.e., a diversity of forage) consumed high- energy foods disproportionately to availability, subsequently increasing their bodymass by 14% and were 35% more likely to conceive than reindeer that fed in low-quality habitats (White 1983). Cook et al. (2001) observed reduced pregnancy rates in elk
(Cervis elaphus nelsoni) fed diets with low digestible energy, indicating reserves acquired during summer and early autumn are important for survival and reproduction later in the year. Results of these studies indicated some animals not only forage to satisfy daily nutritional and energetic requirements, but also to obtain nutrient reserves that influence survival and fitness.
Similarly, migratory waterfowl acquire and depend on a variety of foods throughout their annual cycle but have evolved to exploit unfamiliar feeding sites with variable forage abundance and quality. For example, waterfowl sustain long flights from breeding to staging areas via nutrients acquired from high-energy foods during late summer and early fall (Gruenhagen and Fredrickson 1990). Refueling and maintenance of body condition occurs on staging and wintering grounds by increasing consumption of high-energy foods (Heitmeyer 1985, Delnicki and Reinecke 1986). At the onset of
1 spring, waterfowl migrate from wintering areas to their breeding areas. During spring migration, some waterfowl switch from high-energy diets to diets high in protein to prepare for reproduction (Lovvorn 1987, Miller 1987, Manley et al. 1992). It is unclear however, when the switch from a high carbohydrate winter diet to a high protein breeding diet occurs. This is important to understand because knowing when this switch occurs can guide habitat management practices to produce desirable food types depending on stage of migration.
Late-winter and spring are critically important to arctic-nesting geese that depend on fat and protein accumulated before reaching their breeding areas, as these reserves are used to meet nutritional requirements of reproduction (Ankney and MacInnes 1978).
Some duck species also rely on reserves acquired during migration for reproduction
(Krapu 1981, Afton and Ankney 1991, Ankney and Alisauskas 1991), and poor body condition in late-winter may lead to reduced fitness (Dubovsky and Kaminski 1994).
Several field studies have shown that birds are capable of breeding earlier and achieving greater reproductive success if fed high-quality diets prior to nesting (Nager 2006), suggesting there is an endogenous nutrient threshold influencing the initiation of breeding
(Reynolds 1972, Gorman et al. 2008). A female that rapidly exceeds this threshold after arrival should therefore experience greater reproductive success (Reynolds 1972).
Migratory waterfowl are likely limited by the quantity and quality of habitats available for foraging. Wetlands that migratory waterfowl depend on to acquire nutrients for survival and reproduction are being lost at a rate of 47,000 ha/yr (Tiner 1998), with the majority of this loss being anthropogenic (Howe et al. 1989). My study occurred in the Upper Mississippi River and Great Lakes Region (UMR/GLR), located in the middle
2 of the Mississippi Flyway and annually used by millions of waterfowl (Bellrose 1980).
The Upper Mississippi River and its nutrient-rich floodplain has been dramatically altered by the expansion of agriculture. Of the six states in North America that have lost
> 80% of their original wetlands, five (Iowa, Missouri, Illinois, Indiana, and Ohio) are located in the UMR/GLR (Dahl 1990). Consequently, populations of waterfowl that breed in and migrate through the UMR/GLR must rely on fewer wetlands (most of which are degraded due to decreased water quality and invasive plant species), than historically
available to meet nutritional requirements, potentially having negative impacts on
populations (Krapu 1981). Because there is limited information regarding nutritional
demands of ducks during spring, an important period for waterfowl populations, my
objective in Chapter 1 was to document the diet of spring migrating waterfowl. I
emphasized how diet varied among species and attempted to describe how some of the
exogenous factors (e.g., latitude, longitude, year, date, foraging habitat, and reproductive status) of individuals may have influenced diet.
If specific nutrients (e.g., protein) are required during specific periods, and those
nutrients are limited in the environment, then organisms should exhibit selection for
resources high in required nutrients. Thus, researchers should be able to gain insight into
nutritional requirements of organisms by determining what food sources are being
selected, relative to their availability. Many previous diet studies were inadequate at
evaluating resource selection because they did not assess or consider consequences of
forage availability. Thus, little information is available regarding nutritional
requirements of waterfowl during spring migration; a period of time when nutrient
availability likely influences individual fitness. Insight into diet of waterfowl will allow
3 habitat managers to manage habitat to provide resources that meet the needs of waterfowl during spring migration, potentially influencing the ability of individuals to successfully reproduce. My objective in Chapter 2 was to document if spring migrating waterfowl were selecting foods (i.e., consuming foods in greater proportion than what was available to them) high in specific nutrients (i.e., proteins or carbohydrates) from representative wetland habitats throughout the UMR/GLR during spring. Hereafter, if I observed a duck consuming a food type in greater proportion than available to them, I considered them to be selecting for that food type. Not only will this information provide a guideline for habitat management for spring migrating ducks but it will allow me to infer nutritional demands of ducks during this time period, as nutritional needs likely change as migration advances and reproduction nears.
4 CHAPTER 1: DIET OF MIGRATING WATERFOWL DURING SPRING IN THE UPPER MISSISSIPPI RIVER AND GREAT LAKES REGION
INTRODUCTION
Diet in Relation to Annual Life Cycle of Waterfowl
Waterfowl have adapted to efficiently use foods in heterogeneous environments to
acquire nutrients and energy for life-cycle activities (i.e., migration, courtship, and
reproduction) while having limited nutrient-storage capacities (Barlein 2003). Because
nutritional and energetic demands and food availability vary throughout the year, duck
diets are diverse and variable (Krapu and Reinecke 1992). Assessment of forage
availability and diet of ducks during breeding (Krapu 1979) and fall migration (Weller
1988, Stafford et al. 2006, Havens 2007, Kross et al. 2008) has been documented, enabling managers to identify, conserve, and restore habitats that provide critical forage during these seasons. Diet may impact reproductive success, as spring diet has been shown to influence reproductive habits of American black ducks (Anas rubripes)
(Barboza and Jorde 2002), however little information is available on diet of spring
migratory ducks and how it varies among species, with regards to availability, latitude and longitude, years, time within a season, habitat types, and reproductive status.
Abundance of foods that waterfowl depend on varies within and among seasons and often have patchy distributions. Diet throughout the annual cycle is strongly correlated with availability, as invertebrates are most abundant during summer (Kaminski and Prince
1981) and seeds are most abundant during fall and winter (Gruenhagen and Fredrickson
1990). Food availability during spring is largely unknown, but is likely scarce when compared to other seasons of the year, especially considering that most managed
5 wetlands are flooded in early fall for wintering waterfowl and these wetlands are more
likely to have fewer seeds due to decomposition (Greer et al. 2006).
Although there is a general trend for duck diets to consist of high protein during breeding and carbohydrates outside of breeding, the proportions of proteinacious and
carbohydrate foods consumed varies considerably among taxa (e.g., dabbling ducks vs. diving ducks). Some species such as mallards (Anas platyrhynchos) depend almost exclusively on carbohydrates while others such as blue-winged teal (Anas discors) consume a more varied diet that consists of both protein and carbohydrates.
Additionally, some waterfowl species exhibit a switch in diet, from predominately seeds to predominately invertebrates, in late winter and early spring (Taylor 1978, Gruenhagen
1987, Lovvorn 1987, Miller 1987, Krapu and Reinecke 1992, Manley et al. 1992). The cause of this switch is not known, but is likely related to a reduction in availability of seeds or changes in nutritional demands, hence selection of proteinacious foods (Lovvorn
1987).
Because poor winter habitats may delay nesting in mallards (Kaminski and
Gluesing 1987, Dubovsky and Kaminski 1994) and American black ducks (Barboza and
Jorde 2002), it is likely that poor-quality spring foraging habitat may also negatively impact nesting waterfowl (Afton and Ankney 1991). Inadequate reserves acquired during spring-staging may decrease nest success through delayed nesting (Harris 1969, McNeil and Leger 1987, Rohwer 1992, Koons and Rotella 2003) or cause some hens to defer reproduction altogether (Newton 2006). Implicit in these findings is that, as spring progresses, diet should reflect reproductive needs. In particular, dietary needs of waterfowl at northern latitudes during spring may differ from waterfowl at southern
6 latitudes during spring. There is strong evidence that late-winter and spring conditions have carryover effects on reproductive success of lesser scaup (Anteau and Afton 2004), however, there is sparse information pertaining to ecology of spring migrating waterfowl in the mid-latitude portions of the Mississippi Flyway, particularly with regards to how diet may change with date or latitude.
Existing information on diet during spring migration is sparse and conflicting
(Newton 2006); some studies found that ducks consumed high-carbohydrate foods (Jorde
1981, LaGrange 1985, Gruenhagen and Fredrickson 1990, Strand et al. 2008), whereas others found ducks consumed high-protein foods (Manley et al. 1992, Badzinski and
Petrie 2006a). Two recent studies on feeding ecology of scaup during spring reported high-carbohydrate foods were the main component of their diet (Smith 2007, Strand et al.
2008), but a third indicated high-protein foods as the main dietary component (Badzinski and Petrie 2006a).
STUDY OBJECTIVES
Previous spring feeding ecology studies of waterfowl are lacking in that they focused only on 1 or 2 species and usually only at a single location; therefore, my specific objective was to determine if diet during spring varied among selected dabbling
(mallard, gadwall (Anas strepera) and blue-winged teal) and diving (lesser scaup (Aythya affinis) and ring-necked duck (Aythya collaris)) ducks. Additionally, I was interested in assessing if diets were influenced by availability of foods (including annual variation), collection date, habitat type, latitude, longitude, and reproductive status during spring.
7 METHODS
Study Site Selection
The Upper Mississippi River and Great Lakes Region (UMR/GLR) encompasses
ten states and is located between important breeding and wintering areas of North
American waterfowl (Figure 1.1). Study sites within the UMR/GLR were selected based
on their presumed importance to migratory waterfowl during the spring (UMR/GLR Joint
Venture 1998) and because they represent typical habitat within the region. The location
of the sites exhibited considerable longitudinal and latitudinal variation to enable
incorporation of spatial variation in diet as birds migrated northward during spring
(Figure 1.2). The study region was divided into 2 transects, a western transect and an eastern transect, with each transect having three study sites distributed south to north. The western transect included (1) the Cache River region of southern Illinois, (2) the Illinois
River region of central Illinois and, (3) the Horicon Marsh region of southeast Wisconsin, whereas the eastern transect was comprised of (1) the Scioto River region of southern
Ohio, (2) the Lake Erie region of northern Ohio, and (3) the Saginaw Bay region of
Michigan.
The southernmost study site (89o3’ W, 37 o18’ N) of the western transect was
located in Southern Illinois and included the Cache River and its floodplain. This region
supports a variety of migratory birds, and was deemed an area of international importance
by the RAMSAR convention. Bottomland forest habitat, identified as critical habitat for
mid-migratory waterfowl (Heitmeyer 1985), represented 70% of available wetland area in the Cache River floodplain. This region also is home to extensive baldcypress and
tupelo swamps that are unique to the Upper Mississippi River region. Because of the
8
Figure 1.1. Location of the Upper MS River and Great Lakes Region with respect to wintering and breeding grounds of ducks migrating through the Upper MS River and Great Lakes Region (image taken from United States Fish and Wildlife Service 2008).
9
Figure 1.2. Location of study sites in the Upper MS River and Great Lakes Region (image provided by Jake Straub, The Ohio State University).
10 uniqueness of this habitat to my area of interest (i.e., the UMR/GLR), it was not included
in sampling efforts. Cypress-tupelo swamps did however represent approximately 16%
of the wetland habitat in the Cache River floodplain. The Cache River floodplain also
contained scrub-shrub (6.3%), open water (3.5%), moist-soil (2.0%), and emergent vegetation (1.3%) wetland habitat types (Havera 1999). The rivers floodplain is
expansive and availability of wetland habitat in this region is largely dependant on winter
and spring precipitation to produce flooding of riparian habitats. Due to restoration
efforts in recent years through the wetlands reserve program (WRP), there are numerous
managed wetlands that persist despite altered river conditions. Mean annual temperature
is 13.7° C, with average winter temperatures ranging from 3.2 − 8.3° C, and spring
temperatures ranging from 8.5 − 18.8° C (Illinois State Water Survey 2008). Mean
annual rainfall is 122.7 cm; greatest precipitation occurs in late winter and spring (Illinois
State Water Survey 2008).
The mid-latitude study site (90o 12’ W, 40o 12’ N) of the western transect was
located along the central region of the Illinois River near Chandlerville, IL. In the early
1900’s, pristine bottomland water areas made the Illinois River one of the most important regions for migratory waterfowl in North America (Bellrose et al. 1983, UMR/GLR Joint
Venture 1998). The Illinois River drains over half of the state, most of which is intensively farmed in row crops (Barrows 1910). Threats to this region include row crop and bank erosion (i.e., increasing nutrient and sediment loads in the river and causing the filling of lateral lakes) and navigation dams that increased low midsummer river levels, resulting in a deepening and extension of all water areas (Steffeck et al. 1980). As a
result of the navigation dams, lakes that were previously separated from the river channel
11 by bottomland timber are now connected and mast-producing timber is dead from
inundation (Bellrose et al. 1983). Consequently, wetlands of this region (particularly
lateral lakes) have been adversely impacted. Similar to some of my other study sites (i.e.
the Cache and Scioto Rivers); the wetland area of this region is dictated by winter and
spring precipitation and flood events of the river. Fortunately for waterfowl that depend on this region, the greatest precipitation occurs in winter and spring (Illinois State Water
Survey 2008) and coincide with peak waterfowl migration (Havera 1999). Mean annual temperature is 10.8° C, with average winter temperatures ranging from -1.9 − 4.8° C, and spring temperatures ranging from 4.4 − 16.9° C (Illinois State Water Survey 2008).
The northernmost study site (88o 50’ W, 43o 48’ N) of the western transect was located in the Upper Rock River watershed in southeast Wisconsin near Horicon Marsh.
This area has been identified as the region of Wisconsin that contains the majority of migratory habitat for waterfowl (UMR/GLR Joint Venture 1998). Representative wetland habitats in this area include riverine wetlands, lacustrine wetlands and a number of kettle ponds and prairie potholes. Agriculture represents 59% of the land use of this watershed and has resulted in substantial drainage of pothole wetlands (Wisconsin
Department of Natural Resources 2002). A number of actively managed wetlands are present in this region with the majority of them being located on Horicon National
Wildlife Refuge and State Wildlife Area and surrounding waterfowl production areas.
One of the largest freshwater wetlands in the United States, Horicon Marsh covers 31,904 acres and is owned and managed by the Fish and Wildlife Service and the Wisconsin
Department of Natural Resources. Soil erosion and siltation, invasion of exotic species
(i.e. carp, purple loosestrife) and high inflow of nutrients from surrounding farms are the
12 biggest threats to this wetland complex (Wisconsin Department of Natural Resources
2002). Mean annual temperature is 7.6° C, with average winter temperatures ranging
from -6.3 − 1.9° C, and spring temperatures ranging from 0.2 − 14.3° C (Midwestern
Regional Climate Center 2008). Mean annual rainfall is 83.9 cm; greatest precipitation
occurs in late summer and early fall, while the driest periods are mid-late winter
(Midwestern Regional Climate Center 2008).
The southernmost study site (82o 59’ W, 39o 40’ N) of the eastern transect was
located near Circleville, Ohio and contained the Scioto River and its floodplain. The
Scioto River Valley is recognized as an important area for migrating American black
ducks and mallards, despite the fact that the area contains little wetland area (UMR/GLR
Joint Venture 1998). Wetland area in the Scioto River Valley, as defined by the National
Wetlands Inventory (Cowardin et al. 1979), was the least of the six study sites (i.e., 9.5 km2). The majority of wetland habitat at this study site was riverine with adjacent
forested and scrub-shrub wetlands. Heavy rain and subsequent flooding from the Scioto
River produces many acres of flooded hardwoods and agriculture that attract thousands of
ducks (UMR/GLR Joint Venture 1998). Consequently, if the Scioto stays within its
banks (i.e., in years of little precipitation), as experienced in the spring of 2006, there is
little wetland habitat available to waterfowl. Mean annual temperature is 10.5° C, with
average winter temperatures ranging from -3.06 − 5.67° C, and spring temperatures ranging from -1.11 − 15.5° C. Mean annual snowfall is 36.1 cm and mean annual rainfall is 99.1 cm; with highest snowfalls in January and greatest precipitation in summer and late spring (Midwestern Regional Climate Center 2008).
13 The mid-latitude study site (82o 59’ W, 41o 27’ N) of the eastern transect was
located on Sandusky Bay Lake Erie, approximately 2 km southwest of Port Clinton, OH.
Wetland habitat in this area consists of marshland, which separates the lake from agricultural farmland, and diked wetlands managed for migrating and wintering waterfowl. Agricultural practices have eliminated all but coastal marshes, which are now
being impacted by urban encroachment (UMR/GLR Joint Venture 1998). This region
still remains important to ducks that migrate through both the Mississippi and Atlantic
Flyways despite the loss of historical Lake Erie marshes. The largest concentrations of
staging American black ducks in North America can be found on Lake Erie marshes in
this area (UMR/GLR Joint Venture 1998). Water levels in this region of Lake Erie are in
constant flux because of varying wind direction and velocity. For example, a strong
southwest wind may decrease the water level in this area, while a strong “northeaster”
wind may cause water levels to rise (Farney 1975). Mean annual temperature is 9.89° C,
with average winter temperatures ranging from -4.2 − 5.17° C, and spring temperatures
ranging from -2.56 − 15.28° C. Mean annual snowfall is 55.1 and mean annual rainfall
is 91.8 cm; with highest snowfalls in January and the greatest precipitation occurring in
late summer (Midwestern Regional Climate Center 2008).
The northernmost study site (83o 25’ W, 43o 45’ N) of the eastern transect was
located near Sebewaing, MI in Saginaw Bay of Lake Huron. Saginaw Bay is a large, shallow embayment of Lake Huron. Wetland habitat outside of the bay is limited and
restricted to hunting clubs and state wildlife areas, which are all used in the spring by
thousands of migrant tundra swans, Canada geese and various duck species (J. Straub,
Ohio State University, personal communication). Agriculture is the dominant inland land
14 use. Wetland degradation and loss in this area can be attributed to residential
development (UMR/GLR Joint Venture 1998) and invasion of Common Reed
(Phragmites australis). Mean annual temperature is 7.06° C, with average winter temperatures ranging from -6.11 − 3.11° C, and spring temperatures ranging from -5.33 –
11.5° C. Mean annual snowfall is 85.6 cm and mean annual rainfall is 66 cm with the greatest precipitation occurring in late summer (Midwestern Regional Climate Center
2008).
Study Species
I selected 3 species of dabbling ducks (Anatinae) for my study because of their diversity in body size, migration habits, and timing of reproduction. Dabbling ducks feed in shallow water by submerging their head or tipping up to reach submersed foods, whereas diving ducks feed in deeper water by diving underwater to feed. The mallard is
the largest of the selected dabblers, travels the shortest distance to its wintering areas and
initiates nesting within days after arriving on breeding areas. The blue-winged teal is the
smallest of the selected dabblers, travels the greatest distance to its wintering areas and
initiates nesting within days after arrival at breeding areas. The gadwall is a mid-sized
dabbling duck, travels intermediate distances to its wintering areas and initiates nests 3 to
4 weeks after arriving on its breeding area (Arzel et al. 2006).
I selected the lesser scaup, hereafter may be referred to as scaup, and ring-necked
duck to represent diving ducks (Aythyinae) for my study because they are similar in
migratory and reproductive habits, but different with respect to diet and population
trends. Scaup populations have experienced a substantial decline relative to the long-
15 term average, while ring-necked duck populations have been stable or increasing during the same period (Wilkins et al. 2006). Additionally, scaup diets have previously been documented to include a large proportion of invertebrates during all stages of the annual cycle (Rogers and Korschgen 1966, Gammonley and Heitmeyer 1990), whereas ring- necked ducks appear to transition from seeds during fall and spring to invertebrates during breeding (Hohman 1985). Scaup and ring-necked ducks are similar in body size, wintering areas, and time between arrival and onset of incubation at breeding sites (Arzel et al. 2006).
Waterfowl Collection
To estimate diet during spring migration, I collected foraging female mallards, gadwall, blue-winged teal, scaup, and ring-necked ducks with a shotgun. Collection began as soon as ice thawed and continued until migrant ducks vacated the study areas
(early May). I attempted to collect only individuals that had fed for ≥ 10 minutes to ensure birds contained ingesta. In some cases, dense vegetation reduced visibility (i.e., forested and emergent wetlands), and I only collected individuals that I knew had been in the habitat for an extended time and were suspected to have been feeding.
I collected foraging females using a layout boat, by stalking, or from camouflaged observation blinds. Layout boats were operated with a trolling motor and camouflaged with sheets of artificial grass. I approached ducks in the layout boat from upwind to encourage them to flush in the direction of the collector.
I recorded locations of collected birds with a global positioning system (GPS) unit and created a shapefile containing the collection data using a handheld personal digital
16 assistant (PDA). Immediately following collection, I injected the esophagi with 10%
buffered formalin solution to prevent post-mortem digestion of food items (Swanson and
Bartonek 1970) and placed a zip-tie at the base of the skull to ensure formalin and food
items were retained. I assigned ducks an identification number, placed an identification
tag on their leg, and refrigerated them until the esophageal tract and proventriculus could
be removed. I removed the esophageal tract and proventriculus within 5 days of
collection and stored them in vials of 10% buffered formalin solution marked with the
unique bird number and species.
Laboratory Analysis
Esophagi of collected ducks were analyzed at Southern Illinois University
Carbondale’s (SIUC) Cooperative Wildlife Research Laboratory Annex. To determine
diet, I removed, rinsed, and sorted contents of the esophagus and proventriculus and used
a dissecting microscope to separate animal and plant food items. Animal food item
identification was conducted at SIUC and seed identification was conducted at The Ohio
State University. Animal foods recovered from esophageal contents were identified to
family (Merritt and Cummins 1996), whereas plant material was identified as either
milfoil (Myriophyllum sp.), coontail (Ceratophyllum demersum), algae, duckweed
(Lemna sp.), Wolffia sp., sporangia (Chara sp.), or ‘other vegetation’, and seeds
identified to genus. Food items were dried at 60o C for ≥ 48 hours before being weighed on a top-loading balance.
17 Statistical Analysis
To reduce the influence of rare occurrences when I encountered a duck that
consumed a single food item in a large amount, I summarized diet data using a weighted, aggregate percent mass method explained in Swanson et al. 1974. I also divided the number of birds that consumed a particular food item by the number of birds in the sample to derive percent occurrence of food items. I summarized diet data for 2006 and
2007 for each individual duck species in 3 categories: vegetation, invertebrates, and seeds.
For data to be used in a multivariate analysis of covariance (MANCOVA), I converted aggregate percent dry mass of food items found in the esophagus into proportions of invertebrates and seeds and used those values as dependant variables for 4 of the aforementioned species (mallard, blue-winged teal, scaup, and ring-necked duck).
Because vegetation composed a large portion of gadwall diets, I included proportion of vegetation in diet as a third dependant variable for gadwall. To examine variability in diet composition among species during spring, I used a MANCOVA in which I included the effects of species (blue-winged teal, gadwall, mallard, lesser scaup, and ring-necked duck), study site (Cache River, Illinois River, Wisconsin, Scioto River, Lake Erie, and
Saginaw Bay), collection date, habitat type (agricultural, seasonal emergent, permanent emergent, open-water, and bottomland hardwood), reproductive status (follicle development present or absent), and year (2006, 2007) (PROC GLM, MANOVA option;
SAS Institute, Inc., Cary, NC).
I conducted 2 MANCOVA’s for each species, 1 in which I considered the study site in which the duck was collected and 1 in which I considered the transect in which the
18 duck was collected. Because a study site was not replicated in each of the transects, I had to consider them in separate MANCOVA’s. To determine if spring diet varied by latitude, longitude, or date within each species, I included the effects of study site or transect, date, habitat, reproductive status, and year; including date by site and site by year interactions as additional effects of interest (PROC GLM, MANOVA option; SAS
Institute, Inc., Cary, NC). I only included reproductive status (i.e., hens that had entered rapid follicle development (RFD) vs. hens that had not) as an independent variable in
MANCOVA models for blue-winged teal and mallards, because these were the only species I encountered that had started RFD. When evaluating diet of a particular species,
I reduced initial MANCOVA models using a step-wise procedure by removing the nonsignificant interaction terms (P > 0.10 based on Type III sums of squares) to obtain a final reduced model that contained all main effects and significant interaction terms
(Badzinski and Petrie 2006a). If an interaction term was significant, I conducted separate
MANCOVA’s on year 1 and year 2 data to reduce confounding effects of interaction terms on main effects. Contrasts of the effects in the reduced MANCOVA model were adjusted using the Tukey-Kramer method (PROC GLM; SAS Institute, Inc., Cary, NC).
Because large variances are typically associated with diet data, I considered data to be highly significant at P ≤ 0.05 or marginally significant at P ≤ 0.10 using the Type III sums of squares.
19 RESULTS
Summary Statistics
We collected 919 ducks during the study; 402 in spring 2006 and 517 in spring
2007. Of these, 847 contained sufficient amounts of food to be included in analyses (n =
203 blue-winged teal, 188 mallards, 116 gadwalls, 135 lesser scaup, and 205 ring-necked
ducks) (Table 1.1). Aggregate percent biomass estimates for invertebrates, seeds and
vegetation consumed by each species are reported in Table 1.2. A more detailed
description of diet at each study site is provided in Appendix A.
Invertebrates that composed the largest portion of diet (i.e., greatest aggregate
percent biomass) in dabbling ducks were: gastropods and Chironomidae in blue-winged
teal, Chironomidae and microcrustacea (e.g., Cladocera, Copepoda and Ostracoda) in
gadwall, and Chironomidae, macrocrustacea (e.g., Amphipoda and Isopoda), and non-
dipteran insects in mallards (Table 1.3). The most common seeds were: Polygonum sp.,
Cyperus sp., Scirpus sp., and Leersia sp. in blue-winged teal, Polygonum sp., Cyperus sp. and Scirpus sp. in gadwall, and Polygonum sp., Leersia and Scirpus in mallards (Table
1.4). Lemna was the most commonly consumed vegetation by dabbling ducks, except gadwall, which consumed slightly more algae (Table 1.5).
The most common invertebrates in diving duck diets were Chironomidae and
Gastropods in scaup and Chironomidae and non-dipteran insects in ring-necked ducks
(Table 1.6). The most common seeds found in scaup were Polygonum sp. and
Potamogeton sp. and in ring-necked ducks were Polygonum sp., Potamogeton sp., and
Echinochloa sp. (Table 1.7). Lemna and unidentifiable vegetation were the most
20 Table 1.1. Number of ducks collected in the Upper MS River and Great Lakes Region that contained food items during spring 2006 and 2007. (BWTE = blue-winged teal, MALL = mallard, GADW = gadwall, RNDU = ring-necked duck, LESC = lesser scaup, CA = Cache River, IR = Illinois River, WI = Wisconsin, SR = Scioto River, LE = Lake Erie, SB = Saginaw Bay) ______2006 2007
SPECIES CA IR WI SR LE SB Total CA IR WI SR LE SB Total TOTAL ______
BWTE 22 21 19 2 20 12 96 27 28 17 10 6 19 107 203
MALL 15 15 9 11 26 19 95 17 13 14 20 8 21 93 188
GADW 8 14 0 0 18 2 42 15 8 16 1 17 17 74 116
RNDU 13 11 3 7 37 15 86 24 10 12 26 25 22 119 205
LESC 0 10 2 1 20 16 49 2 25 5 16 9 29 86 135
Total 58 71 33 21 121 64 368 85 84 64 73 65 108 479 847 ______
Table 1.2. Aggregate percent (A) ± standard error and percent occurrence (O) of food items in ducks (BWTE = blue-winged teal, MALL = mallard, GADW = gadwall, LESC = lesser scaup, RNDU = ring-necked duck) collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______vegetation invertebrates seeds A O A O A O ______
BWTE 4.8 ± 1.8 19.7 41.4 ± 2.5 76.3 53.7 ± 2.8 91.1
MALL 4.3 ± 1.9 17.8 16.4 ± 2.6 48.1 79.2 ± 2.9 91.6
GADW 52.9 ± 2.4 70.6 8.9 ± 3.3 75.8 38.0 ± 3.7 75.8
LESC 5.6 ± 2.2 23.3 54.7 ± 3.1 84.9 39.6 ± 3.5 82.7
RNDU 8.7 ± 1.8 24.1 17.6 ± 2.5 53.7 73.6 ± 2.8 91.1 ______
21 Table 1.3. Aggregate percent biomass of animal foods consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 1.0% aggregate mass, they were listed as trace (tr.). ______
Food Item BWTE (n = 155) GADW (n = 88) MALL (n = 92) Agg. % Agg. % Agg. % ______
Gastropoda 37.2 2.1 12.6
Lymnaeidae 10.9 tr. 2.2
Physidae 10.7 1.1 6.9
Planorbidae 15.5 tr. 3.5
Bivalvia 1.4 0.0 0.0
Sphaeriidae 1.4 0.0 0.0
Chironomidae 19.1 31.8 19.8
Non-Chironomidae Dipterans 6.6 14.4 11.7
Ceratopogonidae 2.7 4.1 2.2
Chaoboridae 0.0 1.1 0.0
Simuliidae 0.0 1.0 0.0
Stratiomyidae 2.1 2.8 2.7
Tabanidae tr. 1.0 1.1
Tipulidae tr. 1.1 2.2
Macrocrustacea 9.7 3.9 19.2
Amphipoda 4.5 2.3 6.9
Isopoda 5.1 1.6 12.2
Microcrustacea 7.2 16.3 2.1
Cladocera 3.9 5.4 tr.
Copepoda 2.1 9.6 1.0
Ostracoda 1.1 1.2 tr.
Annelida 5.0 4.2 9.4
Hirudinea tr. 0.0 1.4
22 Table 1.3 continued. ______
Food Item BWTE (n = 155) GADW (n = 88) MALL (n = 92) Agg. % Agg. % Agg. % ______
Oligochaeta 4.2 3.2 8.0
Nematoda tr. 11.2 1.2
Non-Dipteran Insects 10.2 12.1 20.5
Collembola 2.5 1.5 0.0
Caenidae tr. 2.8 tr.
Coenagrionidae 1.6 tr. 1.9
Cicadellidae tr. 0.0 1.0
Corixidae tr. 1.3 0.0
Naucoridae 0.0 0.0 1.0
Dytiscidae 1.1 0.0 1.4
Carabidae tr. 0.0 2.5
Hydrophilidae tr. tr. 2.4
Leptoceridae tr. 0.0 2.0
Limnephilidae tr. 0.0 1.0
Phryganeidae tr. 0.0 2.0
Pyralidae tr. 1.8 1.0
Miscellaneous / Unknown Inverts 4.0 4.6 3.9
Terrestrials 2.6 3.5 2.0
Unknowns 1.4 1.1 1.9 ______
23 Table 1.4. Aggregate percent biomass of plant foods consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.5% aggregate mass, they were listed as trace (tr.). ______
Food Item BWTE (n = 185) GADW (n = 88) MALL(n = 175) Agg. % Agg. % Agg. % ______
Abutillion sp. 0.0 0.0 0.7
Alisma sp. 1.3 2.2 0.7
Amaranthus sp. 5.3 0.7 1.5
Bidens sp. 6.3 tr. 0.9
Carex sp. 3.9 6.0 1.2
Cephalanthus sp. 1.9 2.2 0.7
Chenopodium sp. 0.8 tr. tr.
Corn tr. 0.0 9.4
Cyperaceae sp. 1.0 0.0 0.0
Cyperus sp. 8.1 15.5 2.2
Digitaria sp. 1.3 2.2 0.5
Echinochloa sp. 4.8 4.3 6.9
Eleocharis sp. 4.9 2.9 0.7
Eragrostis sp. 1.8 2.2 0.8
Helenium sp. 0.0 0.0 0.7
Leersia sp. 7.8 6.4 12.9
Ludwigia sp. 4.0 1.8 tr.
Myriophyllum sp. tr. 0.7 tr.
Najas sp. tr. 2.6 1.0
Panicum sp. 4.9 2.8 1.7
Poaceae sp. tr. 1.1 tr.
Polygonum sp. 20.4 21.5 17.2
Potamogeton sp. 2.6 2.4 4.1
24 Table 1.4 continued. ______
Food Item BWTE (n = 185) GADW (n = 88) MALL (n = 175) Agg. % Agg. % Agg. % ______
Rhynchospora sp. 0.5 0.0 0.0
Rumex sp. 0.7 tr. 1.4
Sagittaria sp. tr. 0.6 0.5
Scirpus sp. 8.0 12.4 11.8
Setaria sp. tr. tr. 2.2
Sparganium sp. 0.0 0.0 0.6
Toxicodendron sp. 0.0 0.0 0.5
Trifolium sp. tr. 0.6 tr.
Vitis sp. 0.0 0.0 0.6
Unknown Seeds 5.2 6.4 4.2
Tubers tr. tr. 9.3 ______
25 Table 1.5. Aggregate percent biomass of vegetation consumed by dabbling ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.1% aggregate mass, they were listed as trace (tr.). ______
Food Item BWTE (n = 40) GADW (n = 82) MALL (n = 34) Agg. % Agg. % Agg. % ______
Algae 0.0 35.8 2.9
Ceratophyllum sp. 0.2 1.1 2.9
Myriophyllum sp. 0.0 1.2 0.0
Lemna sp. 77.7 32.8 52.3
Wolffia sp. 0.0 2.8 0.0
Chara sporangia tr. 2.8 0.2
Other Vegetation 22.0 23.3 41.4 ______
26 Table 1.6. Aggregate percent biomass of animal foods consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 1.0% aggregate mass, they were listed as trace (tr.). ______
Food Item LESC (n = 113) RNDU (n = 109) Agg. % Agg. % ______
Gastropoda 20.3 11.8
Lymnaeidae 4.5 tr.
Physidae 9.8 8.1
Planorbidae 5.9 3.0
Bivalvia 4.0 2.2
Dreisseniidae 0.0 1.4
Sphaeriidae 4.0 tr.
Chironomidae 41.7 47.4
Non-Chironomidae Dipterans 3.2 2.0
Ceratopogonidae 1.6 tr.
Macrocrustacea 9.3 6.7
Amphipoda 1.9 2.2
Isopoda 7.4 4.5
Microcrustacea 4.2 tr.
Cladocera 2.4 tr.
Ostracoda 1.0 tr.
Annelida 3.5 4.9
Oligochaeta 3.5 4.9
Nematoda 5.0 1.8
Non-Dipteran Insects 6.0 18.1
Coenagrionidae 1.3 3.4
Libellulidae 1.4 6.6
Phryganeidae 0.0 1.8
27 Table 1.6 continued. ______
Food Item LESC (n = 113) RNDU (n = 109) Agg. % Agg. % ______
Miscellaneous / Unknown Inverts 3.0 4.5
Bryozoan 1.9 3.6
Unknowns 1.1 0.9 ______
28 Table 1.7. Aggregate percent biomass of plant foods consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. If food items were < 0.5% aggregate mass, they were listed as trace (tr.). ______
Food Item LESC (n = 110) RNDU (n = 185) Agg. % Agg. % ______
Amaranthus sp. 2.2 3.6
Bidens sp. 0.5 tr.
Brassica sp. 0.0 0.5
Carex sp. 1.3 tr.
Cephalanthus sp. 0.9 tr.
Ceratophyllum sp. 3.7 2.8
Chenopodium sp. 2.0 tr.
Corn 3.5 2.0
Cyperus sp. 8.9 5.9
Echinochloa sp. 5.8 14.2
Eleocharis sp. tr. 0.5
Eragrostis sp. 0.8 tr.
Impatiens sp. 0.6 0.0
Ipomea sp. 0.8 0.0
Juncus sp. 1.1 0.0
Leersia sp. 4.2 6.4
Ludwigia sp. 1.8 1.2
Myriophyllum sp. 0.7 1.1
Najas sp. 0.8 4.5
Panicum sp. tr. 5.0
Phalaris sp. tr. 0.9
Phragmites sp. 0.9 tr.
Poaceae sp. 0.8 0.5
29 Table 1.7 continued. ______
Food Item LESC (n = 110) RNDU (n = 185) Agg. % Agg. % ______
Polygonaceae sp. 0.7 0.0
Polygonum sp. 20.4 20.4
Potamogeton sp. 15.1 14.7
Sagittaria sp. 0.6 tr.
Scirpus sp. 9.2 5.7
Trifolium sp. 0.0 0.5
Vallisneria sp. 0.0 0.5
Zannichellia sp. 0.7 tr.
Unknown Seeds 8.1 2.2
Tubers tr. 4.1 ______
30 commonly consumed vegetation by diving ducks, although ring-necked ducks also consumed large amounts of Chara sp. (Table 1.8).
MANCOVA results
I applied an arcsine square-root transformation to the diet data; however this did not eliminate the nonnormality of the proportions in the diet. I therefore concluded that my data was robust to transformation. Additionally, because of a prevalence of zeros in my data, I decided against using compositional analyses to evaluate diet. Even though these assumptions were violated by analyzing my diet data in a MANCOVA, this approach, however, has been utilized in recent waterfowl diet studies and appears to be
the most efficient method of evaluating waterfowl diet data (Afton et al. 1991, Badzinski
and Petrie 2006).
Breeding vs. Non-Breeding
Thirty-three mallards and 9 blue-winged teal had entered RFD. Interestingly, the
diets of both mallards (F1,13 = 0.64, P = 0.42 for invertebrates and F1,13 = 0.14, P = 0.71 for seeds) and blue-winged teal (F1,12 = 0.39, P = 0.53 for invertebrates and F1,12 = 0.41, P
= 0.52 for seeds) in RFD were similar to diets of mallards and blue-winged teal not in
RFD and when I excluded RFD females from analyses, it did not change results; therefore I did not consider them separately in subsequent analyses. Although not statistically significant, there were, however, higher mean proportions of invertebrates in diets of blue-winged teal (58% vs. 42%) and mallards (27.7% vs. 15.7%) that had begun
RFD than those that had not begun RFD.
31 Table 1.8. Aggregate percent biomass of vegetation consumed by diving ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______
Food Item LESC (n = 31) RNDU (n = 49) Agg. % Agg. % ______
Algae 3.2 0.0
Ceratophyllum sp. 3.2 4.0
Myriophyllum sp. 0.0 0.0
Lemna sp. 46.3 24.3
Wolffia sp. 0.0 2.0
Chara sporangia 3.3 24.5
Other Vegetation 43.7 44.9 ______
32 Diet
The final MANCOVA model (with non-significant interactions removed) evaluating duck diets considered only main effects of study site, species, date, habitat, reproductive status, and year. Significant effects of the model included study site, species, and date for both the proportions of invertebrates and seeds in the diet (Table
1.9). Blue-winged teal, gadwall, and scaup had similar proportions (P > 0.10) of invertebrates and seeds in their diets. Likewise, the diet of mallards was similar to ring- necked ducks (Figure 1.3). Invertebrate consumption significantly increased with date, whereas seed consumption decreased.
Blue-winged Teal Diets
Two-hundred and three blue-winged teal (n = 96 in 2006 and n = 107 in 2007) were included in the analysis evaluating diet at the scale of study site (Table 1.1).
Likewise, 203 blue-winged teal (n = 69 from eastern transect and n = 134 from western transect) were included in the analysis evaluating diet at the scale of transect (n = 34 in
2006 and n = 35 in 2007 from the eastern transect and n = 62 in 2006 and n = 72 in 2007 from the western transect). In 2006, the first blue-winged teal was collected on 14 March and the last on 5 May and in 2007, the first was collected on 18 March and the last on 3
May (Table 1.10).
The final reduced MANCOVA model evaluating latitudinal variation in diet
(invertebrates and seeds) of blue-winged teal included only the main effects of site, date, habitat, reproductive status, and year. The percentage of invertebrates in the diet varied
33 Table 1.9. Results from the initial MANCOVA model evaluating the effects of site, species (Sp), date (Jul), habitat (Hab), reproductive status (RS), and year (Yr) on proportions of invertebrates and seeds consumed by 5 species of ducks collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 8.41 1.68 12.34 < 0.05
Sp 4 9.69 2.42 17.78 < 0.05
Jul 1 0.74 0.74 5.43 < 0.05
Hab 5 1.10 0.22 1.62 0.15
RS 1 0.29 0.29 2.18 0.14
Yr 1 0.34 0.34 2.55 0.11
Seeds
Site 5 9.15 1.83 12.98 < 0.05
Sp 4 10.87 2.71 19.28 < 0.05
Jul 1 0.87 0.87 6.20 0.01
Hab 5 1.06 0.21 1.51 0.18
RS 1 0.21 0.21 1.49 0.22
Yr 1 0.22 0.22 1.55 0.21 ______
34
100 c 90 c 80 a 70 a/b 60 e b % seed 50 d/e d % invert 40
% in diet f 30 f 20 10 0 BWTE MALL GADW LESC RNDU
Species
Figure 1.3. Percent of seeds and invertebrates in the diet of 6 species (BWTE = blue- winged teal, MALL = mallard, GADW = gadwall, LESC = lesser scaup, RNDU = ring- necked duck) collected in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
35 significantly by date and the percentage of seeds varied significantly among study sites
and by date (Table 1.11). Blue-winged teal exhibited a daily increase of 0.79% ± 0.29%
in invertebrate consumption (P = 0.006). Additionally, the proportion of seeds in the diet
was moderately lower (P = 0.065) for blue-winged teal collected at Saginaw Bay than blue-winged teal collected at Wisconsin (Figure 1.4).
The final reduced MANCOVA model evaluating longitudinal variation in diets of
blue-winged teal included the main effects of transect, date, habitat, reproductive status,
year, and a transect by year interaction (Table 1.12). Because of the significant
interaction term, I analyzed data by year (i.e., removed interaction term), and found
invertebrate consumption varied significantly with transect in 2006 and date in 2006 and
2007 (Table 1.13 and Table 1.14), whereas seed consumption varied with transect in
2006 (Table 1.13) and only date in 2007 (Table 1.14). Blue-winged teal collected in the
eastern transect consumed 30.4% ± 9.1% more invertebrates and 31.3% ± 9.1% less seeds than teal collected in the western transect in 2006 (Figure 1.5). Blue-winged teal
collected in 2006 increased invertebrate consumption by 0.81% ± 0.38% daily. In 2007,
invertebrate and seed consumption varied only by date (Table 1.14 and Figure 1.6).
Invertebrate consumption increased daily by 0.82% ± 0.37% and seed consumption
decreased daily by 0.89% ± 0.37% in 2007.
36 Table 1.10. Date of first and last dabbling duck collected at each study site in 2006 and 2007. ______2006 2007 SPECIES FIRST LAST FIRST LAST ______
BWTE Cache River 23 March 19 April 18 March 26 April
Illinois River 14 March 01 May 22 March 29 April
Wisconsin 05 April 05 May 02 April 03 May
Scioto River 27 March 30 March 21 March 09 April
Lake Erie 16 March 21 April 26 March 12 April
Saginaw Bay 06 April 27 April 25 March 03 May
MALL
Cache River 16 February 01 April 22 February 29 March
Illinois River 12 March 11 April 13 March 18 April
Wisconsin 03 April 25 April 02 April 04 May
Scioto River 23 February 10 March 22 February 27 March
Lake Erie 10 March 21 April 13 March 18 April
Saginaw Bay 17 March 20 April 19 March 23 April
GADW
Cache River 03 March 12 April 22 February 01 April
Illinois River 13 March 03 April 13 March 10 April
Wisconsin N/A N/A 28 March 03 May
Scioto River N/A N/A 27 February 27 February
Lake Erie 10 March 19 April 19 March 18 April
Saginaw Bay 06 April 12 April 20 March 19 April
______
37 Table 1.11. Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), reproductive status (RS), and year (Yr) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 1.44 0.29 1.79 0.11
Jul 1 1.25 1.25 7.80 < 0.05
Hab 4 0.27 0.06 0.42 0.79
RS 1 0.06 0.06 0.39 0.53
Yr 1 0.10 0.10 0.63 0.42
Seeds
Site 5 1.92 0.38 2.38 < 0.05
Jul 1 0.98 0.98 6.12 < 0.05
Hab 4 0.27 0.06 0.42 0.79
RS 1 0.06 0.06 0.41 0.52
Yr 1 0.12 0.12 0.79 0.37 ______
38 80 a/b c c b 70 c a/b a/b 60 c c a/b c 50 a % seed 40 % invert 30 % in diet 20
10
0 SR LE SAG CA IR WI
East Transect West Transect
Study Site
Figure 1.4. Percent of seeds and invertebrates consumed by blue-winged teal at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
39 Table 1.12. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), reproductive status (RS), year (Yr), and transect by year (Tran*Yr) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 1.03 1.03 6.59 < 0.05
Jul 1 1.58 1.58 10.12 < 0.05
Hab 4 0.25 0.06 0.41 0.80
RS 1 0.01 0.01 0.06 0.81
Yr 1 0.002 0.002 0.02 0.90
Tran*Yr 1 0.78 0.78 5.01 < 0.05
Seeds
Tran 1 1.36 1.36 8.67 < 0.05
Jul 1 1.36 1.36 8.65 < 0.05
Hab 4 0.23 0.05 0.37 0.83
RS 1 0.01 0.01 0.06 0.80
Yr 1 0.002 0.002 0.01 0.91
Tran*Yr 1 0.79 0.79 5.04 < 0.05 ______
40 Table 1.13. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and reproductive status (RS) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2006. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 1.65 1.65 11.18 < 0.05
Jul 1 0.66 0.66 4.51 < 0.05
Hab 4 0.75 0.19 1.28 0.28
RS 1 0.04 0.04 0.29 0.59
Seeds
Tran 1 1.75 1.75 11.65 < 0.05
Jul 1 0.31 0.31 2.09 0.15
Hab 4 0.74 0.18 1.24 0.30
RS 1 0.08 0.08 0.52 0.47 ______
41 Table 1.14. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and reproductive status (RS) on proportions of invertebrates and seeds consumed by blue-winged teal in the Upper MS River and Great Lakes Region during spring 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 0.02 0.02 0.15 0.70
Jul 1 0.79 0.79 4.75 < 0.05
Hab 4 0.10 0.02 0.16 0.95
RS 1 0.01 0.01 0.07 0.79
Seeds
Tran 1 0.11 0.11 0.68 0.41
Jul 1 0.94 0.94 5.66 < 0.05
Hab 4 0.18 0.04 0.28 0.89
RS 1 0.01 0.01 0.08 0.78 ______
42 Mallard Diets
One-hundred and eighty-eight mallards (n = 95 in 2006 and n = 93 in 2007) were
included in analyses evaluating diet at the scale of study site (Table 1.1). Likewise, 188 mallards (n = 105 from eastern transect and n = 83 from western transect) were included in the analysis evaluating diet at the scale of transect (n = 56 in 2006 and n = 49 in 2007 from the eastern transect and n = 39 in 2006 and n = 44 in 2007 from the western transect). In 2006, the first mallard was collected on 16 February and the last on 25 April and in 2007, the first was collected on 22 February and the last on 4 May (Table 1.10).
The final reduced MANCOVA model evaluating latitudinal variation in diets
(invertebrates and seeds) of mallards included the main effects of site, date, habitat,
reproductive status, and year; none of which were significant with regard to the
proportions of invertebrates or seeds in the diet (Table 1.15 and Figure 1.7).
The final reduced MANCOVA model evaluating longitudinal variation in diet of
mallards included the main effects of transect, date, habitat, reproductive status, and year.
The reduced model included only a date effect for the proportions of invertebrates and
seeds in the diet (Table 1.16 and Figure 1.8). Mallards exhibited a daily increase of
0.47% ± 0.18% in invertebrate consumption (P = 0.002) and a daily decrease of 0.55% ±
0.19% in seed consumption (P = 0.004).
43 100 d 80 a
60 c % seed b 40 % invert % in diet 20 0 West East Transect
Figure 1.5. Percent of seeds and invertebrates consumed by blue-winged teal at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 (least-squares means ± standard error). Different letters indicate significantly different means.
44 a 80 a 70 b b 60 50 % seed 40 % invert % in diet 30 20 10 0 West East
Transect
Figure 1.6. Percent of seeds and invertebrates consumed by blue-winged teal at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
45 Table 1.15. Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), reproductive status (RS), and year (Yr) on proportions of invertebrates and seeds consumed by mallards in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 0.93 0.18 1.71 0.13
Jul 1 0.16 0.16 1.51 0.22
Hab 5 0.72 0.14 1.32 0.25
RS 1 0.07 0.07 0.64 0.42
Yr 1 0.02 0.02 0.19 0.66
Seeds
Site 5 0.71 0.14 1.18 0.32
Jul 1 0.24 0.24 2.02 0.15
Hab 5 0.57 0.11 0.96 0.44
RS 1 0.01 0.01 0.14 0.71
Yr 1 0.02 0.02 0.17 0.68 ______
46 120 a a a 100 a a a 80
60 % seed
40 b % invert
% in diet b b 20 b b b
0 SR LE SAG CA IR WI -20 East Transect West Transect
Study Site
Figure 1.7. Percent of seeds and invertebrates consumed by mallards at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
47 Table 1.16. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), reproductive status (RS), year (Yr), and transect by year (Tran*yr) on proportions of invertebrates and seeds consumed by mallards in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 0.02 0.02 0.21 0.65
Jul 1 0.76 0.76 6.81 < 0.05
Hab 5 0.33 0.06 0.59 0.70
RS 1 0.02 0.02 0.16 0.68
Yr 1 0.03 0.03 0.30 0.58
Seeds
Tran 1 0.04 0.04 0.38 0.53
Jul 1 1.02 1.02 8.45 < 0.05
Hab 5 0.39 0.08 0.65 0.66
RS 1 0.00 0.00 0.00 0.98
Yr 1 0.01 0.01 0.08 0.77 ______
48 120 a 100 a
80 % seed 60 % invert % in diet 40 b b 20
0 West East
Transect
Figure 1.8. Percent of seeds and invertebrates consumed by mallards at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
49 Gadwall Diets
One-hundred and sixteen gadwalls (n = 42 in 2006 and n = 74 in 2007) were included in analyses evaluating diet at the scale of study site (Table 1.1). Likewise, 116 gadwalls (n = 55 from eastern transect and n = 61 from western transect) were included in the analysis evaluating diet at the scale of transect (n = 20 in 2006 and n = 35 in 2007 from the eastern transect and n = 22 in 2006 and n = 39 in 2007 from the western transect). In 2006, the first gadwall was collected on 3 March and the last on 19 April and in 2007, the first was collected on 22 February and the last on 3 May (Table 1.10).
The final reduced MANCOVA model evaluating latitudinal variation in diet
(vegetation, invertebrates, and seeds) of gadwalls included the main effects of site, date, habitat, and year; sample sizes were insufficient to include date by site and site by year interactions. There was a marginally significant year effect on percentage of invertebrates in gadwall diets (Table 1.17), with invertebrate consumption being greater in year 2 than year 1 (P = 0.080). Proportions of vegetation, invertebrates, and seeds did not differ among study sites (Figure 1.9).
The final reduced MANCOVA model evaluating longitudinal variation in diet
(vegetation, invertebrates and seeds) of gadwalls included the main effects of transect, date, habitat, year, and a transect by year interaction (Table 1.18). Because of the significant interaction term, I separated data by years (i.e., removed interaction term), and found invertebrate consumption of gadwalls in 2006 was not effected by transect, date, or the habitat they were collected in. However, the proportion of seeds and vegetation consumed by gadwalls in 2006 varied significantly with date and transect (Table 1.19).
Gadwalls collected in the western transect in 2006 consumed 40.8% ± 15.4% more seeds
50 Table 1.17. Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 0.11 0.02 0.40 0.84
Jul 1 0.01 0.01 0.23 0.63
Hab 4 0.06 0.01 0.28 0.88
Yr 1 0.16 0.16 3.12 0.08
Seeds
Site 5 1.60 0.32 1.80 0.12
Jul 1 0.29 0.29 1.61 0.20
Hab 4 1.25 0.31 1.75 0.14
Yr 1 0.43 0.43 2.42 0.12
Vegetation
Site 5 1.81 0.36 1.87 0.10
Jul 1 0.42 0.42 2.16 0.14
Hab 4 1.38 0.34 1.77 0.14
Yr 1 0.06 0.06 0.32 0.57 ______
51 250
200
150
100 % seed % invert 50 % veg
% in diet 0 SR LE SAG CA IR WI -50 East Transect West Transect -100
Study Site
Figure 1.9. Percent of seeds, vegetation and invertebrates consumed by gadwalls at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
52 Table 1.18. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), year (yr), and transect by year (Tran*yr) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 0.00 0.00 0.01 0.92
Jul 1 0.09 0.09 1.75 0.19
Hab 4 0.09 0.02 0.45 0.77
Yr 1 0.12 0.12 2.25 0.13
Tran*yr 1 0.00 0.00 0.06 0.80
Seeds
Tran 1 0.87 0.87 5.05 < 0.05
Jul 1 0.16 0.16 0.94 0.33
Hab 4 1.15 0.29 1.67 0.16
Yr 1 0.83 0.83 4.81 < 0.05
Tran*yr 1 1.11 1.11 6.45 < 0.05
Vegetation
Tran 1 0.83 0.83 4.36 < 0.05
Jul 1 0.50 0.50 2.61 0.11
Hab 4 1.28 0.32 1.66 0.16
Yr 1 0.32 0.32 1.68 0.19
Tran*yr 1 0.99 0.99 5.20 < 0.05 ______
53 Table 1.19. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), and habitat (Hab) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2006. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 0.00 0.00 0.08 0.78
Jul 1 0.01 0.01 0.35 0.55
Hab 3 0.03 0.01 0.45 0.72
Seeds
Tran 1 1.13 1.13 6.95 < 0.05
Jul 1 0.98 0.98 6.04 < 0.05
Hab 3 1.26 0.42 2.59 0.07
Vegetation
Tran 1 1.04 1.04 6.20 < 0.05
Jul 1 1.16 1.16 6.93 < 0.05
Hab 3 1.26 0.42 2.51 0.07 ______
54 than gadwalls collected in the eastern transect in 2006 (Figure 1.10). Seed consumption decreased daily by 1.4% ± 0.5% and vegetation consumption increased daily by 1.5% ±
0.6% in gadwalls collected in 2006. Gadwalls collected in the eastern transect in 2006 consumed 39.2% ± 15.7% more vegetation than gadwalls collected in the western transect in 2006 (Figure 1.10). There was no effect of transect, date, or habitat on seeds, invertebrates, and vegetation consumed by gadwalls in 2007 (Table 1.20 and Figure
1.11).
Lesser Scaup Diets
One-hundred and thirty-five lesser scaup (n = 49 in 2006 and n = 86 in 2007) were included in analyses evaluating diet at the scale of study site (Table 1.1). Likewise,
135 lesser scaup (n = 91 from eastern transect and n = 44 from western transect) were included in the analysis evaluating diet at the scale of transect (n = 37 in 2006 and n = 54 in 2007 from the eastern transect and n = 12 in 2006 and n = 32 in 2007 from the western transect). In 2006, the first lesser scaup was collected on 08 March and the last on 29
April and in 2007, the first was collected on 27 February and the last on 2 May (Table
1.21).
The final reduced MANCOVA model evaluating latitudinal variation in diets
(invertebrates and seeds) of scaup included the main effects of site, date, habitat, and year. The percentage of invertebrates and seeds in the diet varied significantly among
study sites and habitats (Table 1.22). More invertebrates (P = 0.006) were consumed by scaup at the Saginaw Bay study site (77.0% ± 9.0%) than all other study sites except the
Scioto River (52.0% ± 12.7%). Moderately fewer seeds (P = 0.073) were consumed by
55 Table 1.20. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), and habitat (Hab) on proportions of invertebrates, seeds, and vegetation consumed by gadwalls in the Upper MS River and Great Lakes Region during spring 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 0.00 0.00 0.00 0.95
Jul 1 0.08 0.08 1.19 0.28
Hab 3 0.06 0.02 0.30 0.82
Seeds
Tran 1 0.04 0.04 0.24 0.63
Jul 1 0.02 0.02 0.14 0.71
Hab 3 0.69 0.23 1.36 0.26
Vegetation
Tran 1 0.04 0.04 0.23 0.63
Jul 1 0.02 0.02 0.10 0.75
Hab 3 0.80 0.27 1.35 0.26 ______
56 120 e 100
80 a d % seed 60 % invert
% in diet 40 b % veg 20 c c 0 West East
Transect
Figure 1.10. Percent of seeds, vegetation and invertebrates consumed by gadwalls at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 (least-squares means ± standard error). Different letters indicate significantly different means.
57 c 100 c 80 % seed 60 % invert a 40 a
% in diet % veg 20 b b 0 West East
Transect
Figure 1.11. Percent of seeds, vegetation and invertebrates consumed by gadwalls at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
58 Table 1.21. Date of first and last diving duck collected at each study site in 2006 and 2007. ______2006 2007 SPECIES FIRST LAST FIRST LAST ______
LESC Cache River N/A N/A 18 March 31 March
Illinois River 15 March 10 April 03 March 30 April
Wisconsin 06 April 11 April 27 March 09 April
Scioto River 08 March 08 March 27 February 04 April
Lake Erie 11 March 21 April 14 March 04 April
Saginaw Bay 19 March 29 April 26 March 02 May
RNDU
Cache River 02 March 01 April 25 February 18 April
Illinois River 14 March 04 April 14 March 09 April
Wisconsin 05 April 13 April 26 March 24 April
Scioto River 23 February 29 March 27 February 29 March
Lake Erie 07 March 20 April 12 March 19 April
Saginaw Bay 29 March 25 April 19 March 02 May
______
59 Table 1.22. Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by lesser scaup in the Upper MS River and Great Lakes Region during spring 2006 and 2007.
______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 4.08 0.81 5.67 < 0.05
Jul 1 0.19 0.19 1.37 0.24
Hab 3 1.07 0.35 2.49 0.06
Yr 1 0.03 0.03 0.24 0.62
Seeds
Site 5 5.08 1.01 8.04 < 0.05
Jul 1 0.03 0.03 0.24 0.62
Hab 3 1.34 0.44 3.53 < 0.05
Yr 1 0.12 0.12 0.98 0.32 ______
60 scaup at the Scioto River study site than at the Wisconsin and Illinois River study sites
(Figure 1.12). Scaup consumed moderately more invertebrates (P = 0.069) in permanent emergent habitat (73.1% ± 11.1%) than in agricultural habitat (16.4% ± 21.1%) and less seeds (P = 0.045) in permanent emergent habitat (21.2% ± 10.4%) than agricultural habitat (81.3% ± 19.7%) and open-water habitat (50.1% ± 6.9%).
The final reduced MANCOVA model evaluating longitudinal variation in diets of scaup included the main effects of transect, date, habitat, and year. The percentage of invertebrates in the diet varied significantly among transects, whereas the percentage of seeds in the diet varied significantly among transects and years (Table 1.23). More seeds and, thus, less invertebrates were consumed by scaup in the western transect (Figure
1.13). Scaup consumed 13.78% ± 7.19% more seeds in year 1 than year 2 (P = 0.058).
Ring-necked Duck Diets
Two-hundred and five ring-necked ducks (n = 86 in 2006 and n = 119 in 2007) were included in analyses evaluating diet at the scale of study site (Table 1.1). Likewise,
205 ring-necked ducks (n = 132 from the eastern transect and n = 73 from the western transect) were included in the analysis evaluating diet at the scale of transect (n = 59 in
2006 and n = 73 in 2007 form the eastern transect and n = 27 in 2006 and n = 46 in 2007 from the western transect). In 2006, the first ring-necked duck was collected on 23
February and the last on 25 April and in 2007, the first was collected on 25 February and
the last on 2 May (Table 1.21).
61 100 d/e b 90 e 80 b a/b 70 d/e a/b/c 60 % seed 50 a/c d d % invert 40 d 30 c % in diet 20 10 0 SR LE SAG CA IR WI
East Transect West Transect
Study Site
Figure 1.12. Percent of seeds and invertebrates consumed by lesser scaup at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
62 Table 1.23. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by lesser scaup in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 1.64 1.64 10.36 < 0.05
Jul 1 0.02 0.02 0.17 0.68
Hab 3 0.67 0.22 1.42 0.23
Yr 1 0.21 0.21 1.38 0.24
Seeds
Tran 1 2.70 2.70 19.19 < 0.05
Jul 1 0.08 0.08 0.58 0.45
Hab 3 0.69 0.23 1.63 0.18
Yr 1 0.51 0.51 3.67 0.06 ______
63 90 80 70 60
50 % seed 40 % invert
% in diet 30
20 10 0 West East
Transect
Figure 1.13. Percent of seeds and invertebrates consumed by lesser scaup at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
64 The final reduced MANCOVA model evaluating latitudinal variation in diet
(invertebrates and seeds) of ring-necked ducks included the main effects of site, date,
habitat, and year. The percentage of invertebrates and seeds in the diet varied
significantly among study sites (Table 1.24). Ring-necked ducks collected at the Saginaw
Bay study site contained more invertebrates and fewer seeds than those collected at the
other study sites (P = 0.022). Also, ring-necked ducks collected at the Scioto River study site contained moderately more invertebrates and less seeds than those collected at
Wisconsin (P = 0.060) (Figure 1.14).
The final reduced MANCOVA model evaluating longitudinal variation in diets of
ring-necked ducks included the main effects of transect, date, habitat, and year. The
percentage of invertebrates and seeds in the diet varied significantly by transect and date.
The percentage of invertebrates in the diet varied significantly between years (Table
1.25). Ring-necked ducks collected in 2006 consumed less invertebrates than those
collected in 2007 (P = 0.050). Also, ring-necked ducks on the eastern transect consumed significantly more invertebrates than ring-necked ducks collected on the western transect
(P = 0.0001) (Figure 1.15).
DISCUSSION
Many factors influence diet of waterfowl. Some of which may be foraging behaviors, morphological adaptations, time of year, and food availability (Poysa 1983).
An example of a morphological adaptation is bill morphology, with some being narrow
(e.g., favoring grazers such as gadwall) and some being broad (e.g., favoring straining as seen in Northern shovelers and teal sp.). Although diets tend to be similar during parts of
65 Table 1.24. Results from a MANCOVA model evaluating the effects of site, date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by ring- necked ducks in the Upper MS River and Great Lakes Region during spring 2006 and 2007.
______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Site 5 6.30 1.26 12.12 < 0.05
Jul 1 0.10 0.10 0.98 0.32
Hab 4 0.30 0.07 0.74 0.56
Yr 1 0.18 0.18 1.80 0.18
Seeds
Site 5 6.98 1.39 12.73 < 0.05
Jul 1 0.11 0.11 1.08 0.30
Hab 4 0.32 0.08 0.75 0.56
Yr 1 0.01 0.01 0.11 0.73 ______
66 120 a/d a/b 100 a/b a/b b/c 80 h 60 % seed g e 40 % invert
% in diet f/g f/g 20 f/g f 0 SR LE SAG CA IR WI -20
East Transect West Transect
Transect
Figure 1.14. Percent of seeds and invertebrates consumed by ring-necked ducks at 6 locations (SR = Scioto River, LE = Lake Erie, SAG = Saginaw Bay, CA = Cache River, IR = Illinois River, WI = Wisconsin) in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
67 Table 1.25. Results from a MANCOVA model evaluating the effects of transect (Tran), date (Jul), habitat (Hab), and year (Yr) on proportions of invertebrates and seeds consumed by ring-necked ducks in the Upper MS River and Great Lakes Region during spring 2006 and 2007. ______Source DF Type III SS Mean Square F value Pr > F ______
Invertebrates
Tran 1 1.94 1.94 15.68 < 0.05
Jul 1 0.58 0.58 4.67 < 0.05
Hab 4 0.41 0.10 0.82 0.51
Yr 1 0.48 0.48 3.89 0.05
Seeds
Tran 1 2.02 2.02 15.21 < 0.05
Jul 1 0.72 0.72 5.44 < 0.05
Hab 4 0.39 0.09 0.75 0.56
Yr 1 0.12 0.12 0.92 0.33 ______
68 100 a 90 80 b 70 60 % seed 50 d % invert 40
% in diet 30 20 c 10 0 West East
Transect
Figure 1.15. Percent of seeds and invertebrates consumed by ring-necked ducks at western/eastern transect in the Upper MS River and Great Lakes Region during spring 2006 and 2007 (least-squares means ± standard error). Different letters indicate significantly different means.
69 the annual life cycle of waterfowl (e.g., reproduction), it is likely that feeding niches reduce competition among species and have a large influence on diet (Nudds 1983), as larger dabbling ducks (e.g., mallards) are able to utilize foods vertically deeper in the water column than smaller dabbling ducks (e.g., blue-winged teal). This niche separation has also been demonstrated in foraging depths of dabbling and diving ducks (Green
1998).
Diets of ducks during clutch formation tend to be less variable than other times during the annual cycle, as ducks must meet protein demands during egg production by taking advantage of abundant invertebrates on wetlands typically utilized during reproduction. Swanson et al. (1985) reported breeding female mallards in North Dakota consumed > 70% animal matter during RFD. Similarly, the diet of female blue-winged teal, scaup, and ring-necked ducks during RFD resemble that of breeding mallards
(Dirschl 1969, Swanson et al. 1974, Hohman 1985). The gadwall, however, is one of the most herbivorous waterfowl species and literature indicates a weaker dependence on invertebrates during RFD, as they may consume as little as 50% animal matter (Ankney and Alisauskas 1991).
The diet of mallards and blue-winged teal I collected that had begun various stages of RFD, varied considerably from the previously mentioned diet studies conducted on traditional breeding areas (e.g., prairie pothole region) during the breeding season.
My sample size of follicle developing blue-winged teal was small (e.g., 9), thus, my inferences are limited; my estimate of the proportion of invertebrates consumed by blue- winged teal in RFD (58% invertebrates) was similar to estimates reported by Dirschl
(1969), but considerably lower than the 95% reported by Swanson et al. (1974).
70 Similarly, I documented mallards in RFD only consumed 27.7% invertebrates in
comparison to the 72% previously reported by Swanson et al. (1985). The difference
between my study and previous studies is likely a difference in nutrient demand
associated with stage of RFD of ducks breeding on my study sites or a difference in food
availability. Because I collected females only at the beginning of the nesting season, the
females I collected may have been in an earlier stage of egg development, thus having a
lower demand for protein than females from other studies. Alternatively, Elmberg et al.
(2000) discovered a relationship between invertebrate abundance and duck-use during the
breeding season in Sweden, suggesting the importance of wetlands with high invertebrate
densities during RFD. Most wetlands in the breeding range of ducks (e.g., prairie pothole
and parkland habitat) are seasonal in nature (e.g., have standing water only through
midsummer). Neckles et al. (2006) found seasonal wetlands in Manitoba supported the
highest densities of invertebrates. It is likely, therefore, that ducks in my study areas may
have had fewer invertebrates available (e.g., compared to breeding ducks in prairie and
aspen wetlands) because most wetlands encountered in the UMR/GLR exhibit a longer
hydroperiod than seasonal wetlands, thus ducks were supplementing their diet with seeds
that are high in carbohydrates, but also provide important amino acids.
In contrast to diets during RFD, diet breadth increases during fall and winter, as
most species consume large amounts of carbohydrates (Delnicki and Reinecke 1986,
Thompson et al. 1992) and some species consume large amounts of invertebrates (Rogers
and Korschgen 1966). Typically, animal matter comprises only a small portion (< 5%) of a ducks diet during winter (Paulus 1982, Delnicki and Reinecke 1986, Thompson et al.
1992, Peters and Afton 1993). This is likely a consequence of the need for high-energy
71 foods (e.g., seeds and agricultural grains) to fuel migration and endure sub-freezing temperatures. Greater variation exists however during this time as compared to breeding diets, as algae and green vegetation are the main components of gadwall diets (Paulus
1982) during winter. Likewise, Rogers and Korschgen (1966) reported scaup diets during winter to consist of > 50% animal matter.
Despite the wealth of knowledge regarding wintering ducks, little is known about duck diets during spring. Existing literature indicates spring diet is similar to winter diet for some species (e.g., mallards), yet very different for others (e.g., blue-winged teal). I found blue-winged teal consumed ~ 35% invertebrates at southern study sites (e.g., the
Cache and Scioto River) and ~ 40% – 60% at northern study sites (e.g., Wisconsin and
Saginaw Bay). My estimates of invertebrate consumption by blue-winged teal were similar to previous spring diet studies at southern latitudes (e.g., Louisiana) but lower than those reported in North Dakota (Manley et al. 1992, Swanson et al. 1974). The only study, however, that examined blue-winged teal diet at similar latitudes as my study was conducted in Missouri and reported teal consumed 70% animal matter (Taylor 1978).
This study evaluated only 10 teal, however, which were collected in seasonally flooded wetlands (i.e., the same habitat type). My estimates of mallard diet during spring are similar to previous studies (e.g., < 1% animal matter in Nebraska and 12% − 24% in
Illinois) and indicate a heavy reliance on seeds and agricultural grains (Jorde 1981, Smith
2007). Mallard diets in my study ranged from 7% − 27% invertebrates, with mean percentages being the least at southern sites (e.g., 9% at Cache River and 7% at Scioto
River) and highest at northern sites (e.g., 23.7% at Wisconsin and 27% at Saginaw Bay).
Because of the lack of spring diet studies of gadwall, I was unable to contrast my results.
72 My data indicated that gadwall diet during spring in the UMR/GLR was composed of
approximately 53% vegetation, 38% seeds, and 9% invertebrates. I did not, however,
anticipate gadwall to consume large amounts of invertebrates because of their
herbivorous food-habits (Ringelman 1990).
I observed a noticeable difference in the spring diet of the diving ducks (e.g.,
scaup and ring-necked ducks). At southern and mid-latitude study sites, I detected scaup
consuming similar proportions of invertebrates and seeds. At northern sites, however, I
detected differing trends, with scaup at Saginaw Bay consuming ~ 80% invertebrates and
scaup at Wisconsin consuming ~ 30% invertebrates. Previous spring diet studies of
scaup indicated a heavier reliance on invertebrates than I observed (Gammonley and
Heitmeyer 1990, Anteau and Afton 2006, Badzinski and Petrie 2006a). I suggest these
differences may be related to habitats in which the scaup were collected (i.e., differences
in availability) and differences in latitude of collected ducks (i.e., I collected scaup at
more southerly latitudes than previous spring studies). Anteau and Afton (2008) only
collected scaup in semi-permanent and permanent wetlands, whereas scaup in this study
were collected from all wetland types in which they were regularly observed foraging in
(i.e., often seasonal emergent wetlands). More recently, spring diet studies of scaup at
southerly latitudes produced similar results, indicating there may be more reliance on
plant foods than historically perceived (Smith 2007, Strand et al. 2008).
No diet data existed on spring-migrating ring-necked ducks but Hohman’s (1985)
results from pre-laying females in Minnesota may provide an indication of what to expect. He found pre-laying females consumed 36% animal matter (Hohman 1985).
This estimate was higher than my estimate of ring-necked duck invertebrate consumption
73 at all staging sites in the UMR/GLR except for Saginaw Bay, where they consumed 60% invertebrates. Given that none of the ring-necked ducks collected at Saginaw Bay had begun RFD and that their diet was similar to female ring-necked ducks that had initiated
egg-laying in Minnesota (Hohman 1985), I speculate invertebrate consumption at
Saginaw Bay was a function of availability.
Temporal and Latitudinal Variation in Spring Diet Within a Species
Some waterfowl rely on endogenous lipid to produce a clutch of eggs, thus as
spring progressed, I expected to see an increase in consumption of invertebrates to
supplement stored lipids. I detected this pattern in blue-winged teal, and to a lesser
extent in mallards and ring-necked ducks, and found some evidence that this increase in
invertebrate consumption was influenced by (1) latitude (i.e., diet shift as they moved
further north during the spring) and (2) date (i.e., diet shift as spring progressed).
Because blue-winged teal have a late and protracted spring migration when compared with other species in this study, I was able to describe this temporal pattern while
controlling for latitude of collection site; whereas these 2 factors (i.e. latitude and time)
were confounded with the other species in this study. For example, my data included teal
that were collected in late April at both southern and northern study sites, whereas
mallards had departed southern study sites by late April, thus were collected only at
northern study sites in late April. No significant differences in invertebrate consumption
existed among study-sites for blue-winged teal after controlling for date (Figure 1.4).
However, there was a significant increase in invertebrate consumption with time,
indicating that diet of blue-winged teal during spring migration is likely more influenced
by date rather than latitude. It is possible that this is a consequence of a nutritional
74 demand for more protein as breeding neared or that there were simply more invertebrates
available as spring progressed; the latter of which is likely not the case (e.g., see Chapter
2).
There was a temporal trend among transects, with mallards and ring-necked ducks increasing invertebrate consumption throughout the spring; however, this trend was not apparent when controlling for study site in which they were collected (e.g., a non- significant effect of date when evaluating diets at the level of study site). This temporal trend was observed in ring-necked ducks collected in the eastern transect and in mallards collected in both the western and eastern transects. These results indicate that mallards and ring-necked ducks appear to be transitioning to diets consisting of more invertebrates as spring progressed.
Diet varied little by latitude among dabbling ducks in my study. Specifically, my data indicated no significant differences in diet composition between study sites for mallards (Figure 1.6) and gadwall (Figure 1.8) when controlling for collection date.
Blue-winged teal collected at Saginaw Bay consumed less seeds than blue-winged teal collected in Wisconsin, but invertebrate consumption did not differ among study sites
(Figure 1.4). These results suggested that latitude did not strongly influence the diet of the dabbling ducks collected in my study.
In contrast to dabbling ducks, some study-site variation existed among diving ducks in my study. These differences, however, occurred with no latitudinal pattern and therefore may exist solely because of differences in availability at these sites. Scaup consumed significantly more invertebrates and fewer seeds at Saginaw Bay than scaup at
Lake Erie, Illinois River, and Wisconsin (Figure 1.10). Ring-necked ducks at Saginaw
75 Bay consumed significantly more invertebrates and fewer seeds than ring-necked ducks
at all other sites. I found availability of both invertebrates and seeds to be scarce to
diving ducks at Saginaw Bay, whereas seeds were more available to diving ducks at Lake
Erie and the Illinois River (see Chapter 2, Table 2.1). This may explain why fewer seeds were consumed by scaup and ring-necked ducks at Saginaw Bay. Additionally, ring-
necked ducks consumed significantly more invertebrates and less seeds at the Scioto
River than the Wisconsin site (Figure 1.12).
Previous work shows photoperiod is one of the most important factors influencing migration patterns (Beason 1978). Because latitude of migration appears to have little impact on diet during spring, yet I found date to influence diet of several species, I speculate that photoperiod (e.g., indirectly date) plays a larger role in diet habits.
Longitudinal Variation in Spring Diet Within a Species
Analyses indicated longitudinal differences in diet for all species in my study except mallards (Figure 1.7). The similarity in the diet of female mallards among transects (i.e., high use of carbohydrate and low use of high-protein foods) likely reflects their preference for high-carbohydrate foods for migration and their efficiency at acquiring their preferred food. Female blue-winged teal (Figure 1.5), scaup (Figure
1.11), and ring-necked ducks (Figure 1.13) consumed a higher percentage of seeds and fewer invertebrates in the western transect than the eastern transect. Invertebrate consumption did not differ among transects for gadwall, but more seeds and less vegetation was consumed by female gadwalls collected in the western transect than those
collected in the eastern transect (Figure 1.9).
76 Possible explanations for the differences in diet among transects in blue-winged
teal, scaup, and ring-necked ducks include (1) ducks collected on the eastern transect may
nest in a different region than ducks collected on the western transect, resulting in different foraging strategies dependant on the distance they are from their breeding areas and the quality of wetlands at respective breeding areas; (2) differences in wintering
populations, resulting in body conditions that were dependant on the quality of wetlands
in respective wintering areas, and; (3) resource availability (see Chapter 2).
Most blue-winged teal winter in Central and South America and it is possible that
teal collected in the western transect wintered along the Gulf Coast of North America and
Central America, whereas teal collected on the eastern transect wintered in South
America (Bellrose 1980). Badzinski and Petrie (2006b) found scaup that wintered in the
Atlantic flyway used parts of the lower Great Lakes during spring migration. Scaup
collected in the western transect, therefore, likely wintered in Central America or along
the Gulf Coast of Louisiana and Mississippi, whereas scaup collected on the eastern transect likely wintered in Florida or along the Atlantic Coast (Bellrose 1980). Ring-
necked ducks staging along the western and eastern transects in the UMR/GLR during spring probably wintered in similar areas as scaup (Bellrose 1980). Lastly, according to the migration corridors provided by Bellrose (1980), it appears that the gadwall encountered in the eastern transect spent winters on the east coast of North America, whereas the gadwall encountered in the western transect likely wintered in Louisiana and
Mississippi. Diet of scaup and ring-necked ducks that winter in the Atlantic and
Mississippi Flyways may differ, possibly explaining some of the discrepancy I observed in diet during spring among the western and eastern transects and possibly supporting the
77 notion that I collected different wintering populations of birds in different transects. In
support of this idea, I found the variation in diet was slightly higher in ring-necked ducks
and scaup collected in the eastern transect than those in the western transect (avg. SE in
western transect = 0.075 and avg. SE in eastern transect = 0.086). Scaup staging in
coastal South Carolina (i.e., Atlantic Flyway) during winter consumed < 1% animal
matter (Kerwin and Webb 1972), whereas scaup staging in coastal Louisiana (i.e.,
Mississippi flyway) during winter consumed 63% animal matter (Rogers and Korschgen
1966). Conversely, ring-necked ducks staging in Louisiana during winter consumed <
1% animal matter (Peters and Afton 1993), whereas ring-necked ducks staging in South
Carolina during winter consumed 58% animal matter (Hoppe et al. 1986). Diet data for gadwall during the winter was only available for the Mississippi Flyway (Paulus 1982,
McKnight and Hepp 1998) as no diet data exists for gadwall wintering along the Atlantic
Flyway. The lack of gadwall diet studies on the wintering grounds in the Atlantic Flyway
makes it difficult to hypothesize if I may have encountered different wintering
populations of gadwall during the spring in the UMR/GLR based on their diets alone.
Likewise, winter diet data for blue-winged teal is sparse and has only been collected in
Central America (Thompson et al. 1992).
Lastly, if distance to breeding area or wetland productivity at respective breeding
areas differed among transects, I may have detected a difference in diet because ducks
that were closer to breeding areas may have consumed more invertebrates to increase protein reserves. It has been suggested that ducks nesting in different areas may differ in
their reliance on endogenous reserves as a consequence of wetland productivity at
breeding areas (Young 1993). For example, migratory mallards breed in both aspen
78 parkland and prairie habitats and the invertebrate food base in prairie wetlands are more likely to exhibit annual variation than aspen parkland wetlands. Existing literature, however, does not allow me to make any predictions regarding where the ducks I am encountering in each transect may breed. In any case, my data indicates that latitude has no affect on diet of spring migrating ducks, so it is likely that distance to breeding areas has little influence on diet.
Although neither of the previously hypothesized explanations can be excluded, I believe the most likely explanation for longitudinal differences in diet was simply a result of differences in availability, as availability varied among the western and eastern transects in 2006 (J. Straub, The Ohio State University, thesis in progress, R. Schultheis,
Southern Illinois University, dissertation in progress). Seed abundance was considerably higher than invertebrate abundance at western transect study sites, whereas seed and invertebrate abundances were more similar at eastern transect study sites.
79 CHAPTER 2: FOOD SELECTION BY MIGRATING WATERFOWL DURING SPRING IN THE UPPER MISSISSIPPI RIVER AND GREAT LAKES REGION
INTRODUCTION
In the previous chapter, I identified several factors that may influence diet of
spring migrating ducks, including interspecific, temporal, latitudinal (i.e., relative
distance from breeding sites) and longitudinal (i.e., variation caused by encountering
different wintering populations) variation, and variation in availability of food types.
This information may be used to manage wetlands to produce highly-consumed food
types, but it provides little insight regarding nutritional or physiological needs of ducks
during spring. By assessing consumption relative to food availability, hence selection for
a food type; biologists can gain insight on nutritional demands of ducks.
Food Selection
A number of previous studies established that ducks are capable of selecting specific food types (Pederson and Pederson 1983, Manley et al. 1992, Thompson et al.
1992, McKnight and Hepp 1998, Anderson et al. 2000, Smith 2007). During fall and winter, most ducks consume foods high in carbohydrates; however, the degree to which this selection occurs varies among species and molt intensity (Anderson et al. 2000).
Although high-carbohydrate seeds and grains comprise a large portion of winter diets of
dabbling ducks, and diving ducks consume varying amounts of animal matter during winter, few studies have evaluated diet in relation to availability during winter simultaneously (Pederson and Pederson 1983, Thompson et al. 1992, McKnight and
Hepp 1998, Anderson et al. 2000). Alternatively, during breeding, dabbling and diving
80 ducks forage almost exclusively on invertebrates (Swanson et al. 1974, Swanson et al.
1985, Ankney and Alisauskas 1991). Assuming breeding season diet is partially based
on a physiological demand for protein, it is unclear when demands shift from high-energy
foods during winter to high-protein foods during breeding. A number of factors may
influence the timing of this transition in food types consumed (e.g., food availability,
digestive physiology, amount of time spent at breeding areas before initiating rapid
follicle development (RFD), use of endogenous/exogenous nutrients in clutch formation, proximity to breeding areas, etc.).
Birds that have been habituated to one food type (e.g., high-carbohydrate foods during winter) cannot immediately transition to an alternative digestive physiology that permits them to efficiently use other food types (e.g., high-protein foods during spring and summer); therefore, it is plausible that ducks may increase invertebrate consumption during spring in order to increase efficiency of high-protein diets at breeding areas (Afik and Karasov 1995). This digestive efficiency concept could be especially important to waterfowl that spend little time on their breeding areas before initiating nests (Toft et al.
1982).
Generally, diving ducks spend more time on breeding areas before initiating RFD than dabbling ducks (Alisauskas and Ankney 1992). This is important because waterfowl that immediately initiate RFD upon arrival (e.g., mallards and blue-winged teal) at breeding areas probably depend heavily on existing lipid reserves or somatic protein.
Likewise, a species that spends 3 − 4 weeks at a breeding area before RFD (e.g., gadwall, lesser scaup, ring-necked duck) likely uses that time to acquire nutrients needed for RFD and subsequent incubation.
81 Because some species of waterfowl store nutrients before reaching breeding areas, conditions experienced prior to breeding must be considered when evaluating reproductive success (Raveling 1979). Poor-quality spring habitat and forage may negatively impact productivity of waterfowl (Afton and Ankney 1991, Dubovsky and
Kaminski 1994, Barboza and Jorde 2002). Dubovsky and Kaminski (1994) found poor winter habitat conditions may have delayed nesting in mallards, presumably due to a lower rate of nutrient acquisition. Inadequate reserves acquired during spring-staging may decrease nest success through delayed nesting (Harris 1969, McNeil and Leger
1987, Rohwer 1992, Koons and Rotella 2003), lead to a reduction in clutch size, or cause some hens to defer reproduction altogether (Newton 2006). The degree to which ducks depend on endogenous protein and lipid for breeding differs; some ducks relying more on lipid stores (wood ducks - Drobney 1980, mallards - Krapu 1981, ring-necked ducks -
Hohman 1986), and others more on somatic protein (American wigeon and gadwall -
Alisauskas and Ankney 1992). Understanding food selection during spring can provide insight on how lipid reserves and somatic protein are acquired before breeding. For example, reserves obtained during spring are central to reproduction in Arctic nesting geese (Ankney and MacInnes 1978, Raveling 1979). Despite evidence that late-winter and spring conditions have carryover affects on reproductive efforts of ducks (Kaminski and Gluesing 1987, Dubovsky and Kaminski 1994), little information is available regarding food selection of spring migrating ducks in mid-latitude portions of the
Mississippi Flyway.
Lastly, proximity to nesting areas during spring migration may influence diet.
Food consumption of ducks at northern latitudes during spring may reflect dietary needs
82 for reproduction, whereas diet at southern latitudes during spring may reflect habitat
conditions at respective wintering areas. Correspondingly, it is important to consider that
“breeding areas” of blue-winged teal, gadwalls, and some mallards (e.g., Missouri Coteau
area of the Prairie Pothole Region) are likely closer to the UMR/GLR than are “breeding
areas” of lesser scaup and ring-necked ducks (e.g., Alaska and boreal forest region of
Canada).
I selected the suite of species for this study because they represented a variety of foraging behaviors observed in spring-migrating ducks (i.e., dabbling and diving ducks).
By examining diverse species, I expected to be able to detect differences in diet selection during spring based on different life-history strategies and traits. By determining if and where (i.e., at what latitude) diet transitions from one food type to another occur during spring, I will be able to recommend habitat management practices that maximize the productivity of foods and meet nutritional requirements of a wide variety of ducks.
STUDY OBJECTIVES
The goal of my study was to determine what 2 classes of foods, seeds or invertebrates, were selected by mallards, blue-winged teal, lesser scaup, and ringed-neck ducks during spring migration through the UMR/GLR. I was unable to evaluate food selection in gadwall because the largest component of their diet was vegetation, and I did not evaluate availability of vegetation. My specific objective was to determine if these species transitioned from selecting high-carbohydrate foods to high-protein foods prior to or during spring migration, and if the timing of this potential transition varied in a predictable manner as a function of life-history characteristics.
83 Based on life-history characteristics, I predicted that blue-winged teal and mallards would increase consumption of invertebrates as spring progressed, allowing them to efficiently transition to a high-protein diet and initiate RFD soon after arrival on breeding areas. Because gadwalls are herbivorous, protein-limited (i.e., depend on somatic protein for clutch formation; Ankney and Alisauskas 1991), and spend 3 − 4 weeks at breeding areas prior to nest initiation, I predicted they would increase invertebrate consumption as they migrated north during spring. Because of their herbivorous nature and dependence on green vegetation, however, I expected to see only small increases in invertebrate consumption with latitude. Scaup have been documented to consume > 50% animal matter at both wintering and breeding sites, therefore, I expected to see a heavy dependence on invertebrates by spring migrating scaup relative to other species in the UMR/GLR. I expected seeds to be an important component of scaup diets, however, because: (1) scaup consume a considerably large proportion of invertebrates throughout the annual cycle (Rogers and Korschgen 1966) and (2) scaup spend considerable time at breeding areas before initiating RFD and the habitats scaup depend on during breeding are highly productive for invertebrates, and (3) breeding female scaup do not further accumulate lipid reserves while on breeding areas (Afton and
Ankney 1991). Similarly, I expected the diet of ring-necked ducks to consist largely of seeds, given that their time on breeding areas before initiating RFD is allocated to protein acquisition (Hohman 1985).
84 METHODS
Food Availability
I collected data used in these analyses in 2006 at the same study sites described in
the previous chapter. I collected food availability samples during 3 time-periods of spring (early, middle, late) to quantify variation in forage abundance throughout migration. Timing of sampling varied among study sites to account for climatic differences and migratory stages of waterfowl (e.g., the difference in the timing of peak waterfowl abundance between northern and southern sites). For example, the early food sampling period began in early to mid-February at southern sites and mid-March at northern sites. As deemed by the latitude of the study area, early food samples were taken as soon as ice conditions permitted to determine food availability during early stages of migration. Mid-spring food samples were collected during the peak of waterfowl migration, whereas late food samples were taken after the majority of birds had passed through. Samples were collected using stratified random sampling from wetland types to estimate forage availability at each study site and to provide an index of food availability in different wetland types (i.e., palustrine forested, palustrine emergent, and lacustrine open-water/riverine wetlands). I determined sample locations by overlaying a grid of 400m x 400m (16 hectares) cells and excluding cells with < 2 ha of wetland habitat as identified by the national wetlands inventory (NWI) (Cowardin et al.
1979) or < 8 ha of soil that held moisture, as identified by soil moisture index data
(Ducks Unlimited 2005). I categorized remaining cells as forested wetland, non-forested wetland, riverine/lacustrine, or agricultural according to dominant vegetation and wetland types present. I selected agricultural habitats based on soil moisture index data as areas
85 that had wet or very wet soils. Within each selected cell, I identified and sampled each
wetland type. For example, if cell 231 at the Cache River study area was identified as
forested wetland based on NWI data, but the cell contained palustrine forested and
palustrine emergent wetland, I identified and sampled each wetland type.
I sampled 60 wetland cells at each of the 6 study sites, 20 of which were
agricultural wetlands and the rest were sampled in proportion to abundance of wetland
type. For example, forested wetland represented approximately 80% of wetland area in
the Cache River study area; therefore, 32 of the 60 cells selected for sampling were
dominated by forested wetland. I did not select blocks proportionally in flooded
agricultural habitat due to the high abundance of ephemeral pools in agricultural fields
that may have resulted in over-sampling if considered proportionally. Additionally,
reliable data were not available to estimate the total proportion of flooded agricultural
crops in an area. Because waterfowl use of agricultural land may be substantial
(LaGrange and Dinsmore 1989, Krapu et al. 2004), I allocated 20 cells as flooded
agriculture regardless of the estimated proportion of flooded agriculture at a study site.
Within a wetland basin, I collected food samples along randomly selected transects. Once in the center of a wetland basin, I used the time (in seconds) on a handheld PDA to determine the direction in which the transect occurred (00
corresponding to straight north, 15 to straight east, 30 to straight south, 45 to straight west, and so on). Then, I took 2 samples along the transect; a deep sample taken at the first location encountered along the transect that was approximately 45 cm deep and a shallow sample taken at a randomly selected depth provided by the PDA between 45 cm
86 and 1 cm. Deep food samples were used to estimate food availability to diving ducks whereas shallow food samples were used for dabbling ducks.
A wetland sample consisted of a d-frame sweep net sample taken along the length of a drop box for 3 sweeps, (33 cm diameter, 500 µm mesh) and a core sample (7 cm diameter, ~5 cm deep) taken from within the drop box (100 cm x 50 cm x 75 cm, 500 µm mesh side panels). The drop box was used to ensure consistency in sampling area of each sample. I rinsed samples through a 500 µm mesh sieve bucket to remove clay material and unwanted debris, placed core and sweep samples in separate bags, and preserved the sample in 10% buffered formalin solution.
Laboratory Analysis
I washed food availability samples through 1mm, 750 µm and 500 µm sieves to facilitate processing of sample contents by size. All seeds and invertebrates were recovered from samples in the laboratory at Southern Illinois University Carbondale
(SIUC). Animal food items were identified at SIUC (Schultheis, Southern Illinois
University, dissertation in progress; Merrit and Cummins 1996), whereas seed identification was conducted at the Ohio State University (Straub, The Ohio State
University, thesis in progress). Foods recovered from availability samples were identified similarly to esophageal contents, but I did not record plant material (i.e., algae,
Lemna sp., etc.). I dried food items for ≥ 48 hours at 60oC and then weighed them on a top-loading balance.
87 Statistical Analysis
There was evidence that both invertebrate and seed availability did not significantly increase or decrease throughout spring (Straub 2008, Schultheis, dissertation in progress), therefore I calculated means and standard errors of invertebrates and seeds in both diet and availability samples (PROC UNIVARIATE; SAS Institute, Inc., Cary,
NC) and compared them using a Z-test in program CONTRAST to investigate if the proportion of food items in duck diets differed from the proportion of food items available at the study site in which the ducks were collected (i.e., selecting for a food type) (Hines and Sauer 1989). I assumed that a diet that was significantly different (P <
0.05) than availability indicated selection of that food item. Additionally, I assumed a diet was moderately significant if 0.05 < P < 0.10. I did not evaluate selection by a species if < 5 ducks of a particular species were collected at a study site. I considered all seeds and invertebrates recorded from shallow and deep samples as available to foraging dabbling and diving ducks, respectively.
I estimated forage availability for diving ducks by including deep availability samples taken in lacustrine open-water and palustrine emergent habitats, but did not include samples from palustrine forested habitats because I considered it unavailable to diving ducks (i.e., diving ducks were never observed using this habitat and I considered it to be inaccessible to diving ducks). Likewise, I estimated forage availability for dabbling ducks by including all shallow availability samples that were collected. Ducks collected in agricultural habitats were not included in these analyses because food sampling methods in these habitats were not replicable among sites in 2006. Additionally, to eliminate possible bias in diet estimates, I removed 5 mallards collected in emergent
88 wetlands because corn was the predominant food item in esophageal contents. With
regard to gadwall diet and selection analyses, I was unable to assess selection because
vegetative items composed the largest proportion of their diet and vegetative items were not sorted from availability samples (i.e., I could not determine availability, hence selection, of vegetative food items).
RESULTS
Availability
Generally, there were more seeds available at each study site than invertebrates
(Table 2.1). Availability estimates were not calculated for diving ducks at Wisconsin because < 5 ring-necked ducks and lesser scaup were collected in 2006. Mean seed availability was highest for dabbling ducks at the Wisconsin site (309.8 ± 51.4 kg/ha) and diving ducks at the Illinois River site (131.1 ± 38.7 kg/ha). Mean invertebrate availability was highest for dabbling ducks at the Saginaw Bay site (116.4 ± 37.6 kg/ha) and diving ducks at the Cache River site (68.7 ± 20.8 kg/ha).
Blue-winged Teal Food Selection
I included data from 94 blue-winged teal collected in spring 2006 in selection
analyses. Of these, 22 were collected at the Cache River, 21 at the Illinois River, 19 at
Wisconsin, 20 at Lake Erie, and 12 at Saginaw Bay. Only 2 teal were collected at the
Scioto River, therefore I did not include these in analyses. Using the mean available
forage and associated standard error from shallow food samples in program CONTRAST,
I found blue-winged teal consumed a significantly higher percentage of invertebrates than
89 Table 2.1. Mean food availability (kg/ha) and standard error (SE) of seeds and invertebrates found in shallow (for dabbling ducks) and deep (for diving ducks) habitats during spring 2006. ______Species Type Site Mean SE ______
Dabbling Ducks Seeds Cache River 163.1 44.7 Invertebrates Cache River 49.7 14.3
Dabbling Ducks Seeds Illinois River 97.2 19.8 Invertebrates Illinois River 33.9 6.8
Dabbling Ducks Seeds Wisconsin 309.8 51.4 Invertebrates Wisconsin 50.6 16.3
Dabbling Ducks Seeds Scioto River 115.4 33.9 Invertebrates Scioto River 12.1 3.4
Dabbling Ducks Seeds Lake Erie 177.3 42.9 Invertebrates Lake Erie 31.4 9.5
Dabbling Ducks Seeds Saginaw Bay 145.5 32.5 Invertebrates Saginaw Bay 116.4 37.6
Diving Ducks Seeds Cache River 124.6 37.3 Invertebrates Cache River 68.7 20.8
Diving Ducks Seeds Illinois River 131.1 38.7 Invertebrates Illinois River 22.3 9.3
Diving Ducks Seeds Wisconsin N/A N/A Invertebrates Wisconsin N/A N/A
Diving Ducks Seeds Scioto River 70.0 32.3 Invertebrates Scioto River 58.2 35.1
Diving Ducks Seeds Lake Erie 120.6 44.3 Invertebrates Lake Erie 12.2 4.0
Diving Ducks Seeds Saginaw Bay 25.9 12.9 Invertebrates Saginaw Bay 20.5 8.3 ______
90 were available at Wisconsin (P < 0.001) and Lake Erie (P < 0.001) (Table 2.2). Blue- winged teal consumed food in proportion to availability at the Cache River, Illinois
River, and Saginaw Bay (P > 0.05).
Mallard Food Selection
I included data from 84 mallards collected in spring 2006 in selection analyses.
Of these, 13 were collected at the Cache River, 11 at the Illinois River, 8 at Wisconsin,
11 at the Scioto River, 24 at Lake Erie, and 17 at Saginaw Bay. Using the mean available forage and associated standard error from shallow food samples in program CONTRAST,
I found mallards consumed food in proportion to availability at all study sites (P > 0.05)
(Table 2.2).
Lesser Scaup Food Selection
I included data from 46 scaup collected in spring 2006 in selection analyses. Of these, 10 were collected at the Illinois River, 20 at Lake Erie, and 16 at Saginaw Bay.
Only 2 scaup were collected at Wisconsin and 1 at the Scioto River, therefore I did not include these in analyses. Using the mean available forage and associated standard error from deep food samples in program CONTRAST, I found scaup consumed a significantly higher percentage of invertebrates than were available at Lake Erie (P <
0.001) (Table 2.2). Scaup consumed food in proportion to availability at Illinois River and Saginaw Bay (P > 0.05).
91 Table 2.2. Results of selection analyses for ducks collected at study sites in the Upper MS River and Great Lakes Region (CA = Cache River, IR = Illinois River, WI = Wisconsin, SR = Scioto River, LE = Lake Erie, and SB = Saginaw Bay) during spring 2006. An “I” indicates selection of invertebrates, “=” indicates consumption in proportion to availability, and “S” indicates selection of seeds. ______CA IR WI SR LE SB ______
Blue-winged teal = = I I =
Mallard ======
Ring-necked duck S = = = =
Lesser scaup = I = ______
92 Ring-necked Duck Food Selection
I included data from 83 ring-necked ducks collected in spring 2006 in selection
analyses. Of these, 13 were collected at the Cache River, 11 at the Illinois River, 7 at the
Scioto River, 37 at Lake Erie, and 15 at Saginaw Bay. Only 3 ring-necked ducks were
collected at Wisconsin, therefore I did not include these in analyses. Using the mean
available forage and associated standard error from deep food samples in program
CONTRAST, I found ring-necked ducks consumed a significantly fewer invertebrates
than were available at the Cache River (P = 0.007) (Table 2.2). Ring-necked ducks consumed food in proportion to availability at the Illinois River, Scioto River, Lake Erie, and Saginaw Bay sites (P > 0.05).
DISCUSSION
Food Selection
For species I observed consuming higher percentages of a food type than was available to them, I interpreted this as selection. Likewise, I considered ducks to be consuming food in proportion to availability if diet was not significantly different than availability (e.g., P > 0.10). I observed all species except mallards, exhibit selection for
either invertebrates or seeds (Table 2.2). The mallard was the only species with large
enough sample sizes (e.g., ≥ 5) to evaluate selection at all study sites; therefore, my
inferences regarding diet trends for some species in spring 2006 were limited. In the
previous chapter, I considered southern sites to be the Cache River and Scioto River, the
mid-latitude sites to be the Illinois River and Lake Erie, and the northern sites to be
Wisconsin and Saginaw Bay, based on their location within their respective transect (e.g.,
93 western or eastern transect). For purposes of detecting a diet trend according to the
latitude in which they were collected, I considered transects jointly and hereafter refer to
the Cache River as the southern site (37 o18’ N), Scioto (39o 40’ N) and Illinois River (40o
12’ N) and Lake Erie (41o 27’ N) as mid-latitude sites, and Saginaw Bay (43o 45’ N) and
Wisconsin (43o 48’ N) as northern sites. It is important to consider, however, that this is
only for conceptual purposes, as both the Saginaw Bay and Wisconsin site would be
“southern sites” to ducks breeding in Alaska.
Blue-winged teal.- Previous spring studies of blue-winged teal indicated selection of invertebrates (Swanson et al. 1974, Manley et al. 1992). Another diet study of blue- winged teal also demonstrated a heavy reliance on invertebrates during spring, but availability data was not collected (Taylor 1978). Interestingly, breeding blue-winged
teal rely heavily on somatic lipid, whereas somatic protein remains relatively constant
through clutch formation, suggesting exogenous resources are used to meet protein
demands (Rohwer, unpublished data). Considering this, and the fact that teal initiate nesting shortly after arrival at breeding areas (Toft et al. 1982), I expected lipid acquisition (i.e., consumption of high-lipid seeds) to be relatively important to spring migrating blue-winged teal.
Contrary to my expectation, blue-winged teal appeared to rely more on invertebrates than seeds during spring as teal exhibited selection for invertebrates at both
Wisconsin and Lake Erie study sites (Table 2.2). My results are similar to previous spring studies of blue-winged teal, indicating selection of invertebrates (Swanson et al.
1974, Manley et al. 1992).
94 Mallard. - Mallard diet studies during spring provided mixed results, with one reporting selection for Chironomidae larvae (Pederson and Pederson 1983) and others documenting a heavy reliance on seeds and agricultural grains (Jorde 1981, Heitmeyer 1985, LaGrange
1985). Only one of these studies, however, collected data on food availability to assess diet selection (Pederson and Pederson 1983). Breeding mallards rely heavily on somatic lipids acquired prior to arrival on breeding grounds (Krapu 1981) and initiate nesting shortly after arriving at breeding area (Toft et al. 1982); therefore I expected mallards staging in the UMR/GLR to consume large amounts of seeds. Because digestive physiology of ducks, however, restricts them from making abrupt changes in diet composition (i.e., from seeds to invertebrates), I expected to see a heavier reliance on animal foods as they approached reproduction in late spring (Barlein 2003).
Although I was unable to detect selection of food items, seeds seemed to be most important to spring migrating mallards in the UMR/GLR in 2006, as mallards consumed
> 78% seeds at all study sites in 2006 (e.g., a diet would have to be exclusively seeds to indicate any kind of seed selection because invertebrate availability was so low at these sites) (Table 2.3). A recent food selection study conducted at one site during spring in the UMR/GLR found similar results with mallards selecting moist-soil seeds (Smith
2007).
I was unable to detect a diet transition, as I observed mallards consuming food in proportion to availability at all sites (i.e., latitudes) (Table 2.2). I did, however, observe the highest proportions of invertebrates in the diet of mallards collected at Saginaw Bay and Wisconsin (i.e., northern sites) (Table 2.3). Young (1993) suggested that somatic protein is not used by mallards during egg laying; rather, protein was obtained from
95 Table 2.3. Mean percentage of food items and standard error (SE) in diet of dabbling ducks at study sites in the Upper MS River and Great Lakes Region during spring 2006. ______Food Type Site Mean % SE ______
Mallard Seeds Cache River 91 7 Invertebrates Cache River 9 7
Mallard Seeds Illinois River 80 11 Invertebrates Illinois River 20 11
Mallard Seeds Scioto River 90 9 Invertebrates Scioto River 10 9
Mallard Seeds Lake Erie 86 6 Invertebrates Lake Erie 14 6
Mallard Seeds Wisconsin 78 15 Invertebrates Wisconsin 22 15
Mallard Seeds Saginaw Bay 78 7 Invertebrates Saginaw Bay 22 7
Blue-winged teal Seeds Cache River 67 8 Invertebrates Cache River 33 8
Blue-winged teal Seeds Illinois River 72 8 Invertebrates Illinois River 28 8
Blue-winged teal Seeds Lake Erie 46 9 Invertebrates Lake Erie 54 9
Blue-winged teal Seeds Wisconsin 33 10 Invertebrates Wisconsin 67 10
Blue-winged teal Seeds Saginaw Bay 30 12 Invertebrates Saginaw Bay 70 12 ______
96 exogenous sources. This, along with the fact I found mallards consuming large amounts of seeds, emphasizes the importance of spring-staging areas for lipid acquisition.
Lesser scaup. - It has been suggested that decreased body condition of breeding scaup, resulting from poor spring-habitat conditions, may be partly responsible for declines in scaup breeding populations (Anteau and Afton 2006, Anteau and Afton 2008). Current spring-staging populations of scaup encounter habitats that do not provide historically preferred foods and may therefore be unable to acquire nutrients that were available previously (Anteau and Afton 2006). I found scaup in the UMR/GLR either consumed more invertebrates than were available or in proportion to availability (Table 2.2). These invertebrates, however, were not the “historically preferred” invertebrates (e.g., amphipods) consumed by scaup during spring, but primarily Gastropoda and
Chironomidae larvae (see previous chapter). Despite the selection of invertebrates I observed in staging scaup, their diets consisted of higher proportions of seeds (Table 2.4) than reported in another recent scaup spring-diet study (Anteau and Afton 2008). Other previous studies indicated scaup fed primarily on invertebrates during spring (Rogers and
Korschgen 1966, Gammonley and Heitmeyer 1990, Afton et al. 1991, Anteau and Afton
2006, Badzinski and Petrie 2006a, Anteau and Afton 2008); however, 2 recent studies reported scaup spring-diet consisted primarily of moist-soil plant seeds (Smith 2007,
Strand et al. 2007), and 1 suggested scaup selected this food type (Smith 2007). I believe the contradictory result of food selection by spring-migrating scaup in recent studies is likely a result of geographic location. For example, the most southern sites of Anteau and Afton (2006) were at an equivalent latitude to my northern sites. Additionally,
97 Table 2.4. Mean percentage of food items and standard error (SE) in diet of diving ducks at study sites in the Upper MS River and Great Lakes Region during spring 2006. ______Food Type Site Mean % SE ______
Lesser Scaup Seeds Illinois River 77.0 13.0 Invertebrates Illinois River 23.0 13.0
Lesser Scaup Seeds Lake Erie 42.0 8.0 Invertebrates Lake Erie 58.0 8.0
Lesser Scaup Seeds Saginaw Bay 26.0 10.0 Invertebrates Saginaw Bay 74.0 10.0
Ring-necked Duck Seeds Cache River 99.5 0.4 Invertebrates Cache River 0.5 0.4
Ring-necked Duck Seeds Illinois River 91.0 9.0 Invertebrates Illinois River 9.0 9.0
Ring-necked Duck Seeds Scioto River 88.0 7.0 Invertebrates Scioto River 12.0 7.0
Ring-necked Duck Seeds Lake Erie 88.0 5.0 Invertebrates Lake Erie 12.0 5.0
Ring-necked Duck Seeds Saginaw Bay 36.0 13.0 Invertebrates Saginaw Bay 64.0 13.0 ______
98 Anteau and Afton (2006) examined scaup diets at breeding sites (Anteau and Afton
2006), whereas no scaup bred at any sites in my study (i.e., macroscopic examination of
internal reproductive organs did not indicate follicle development in any of the collected
scaup).
I did not collect scaup at the southern study site in 2006 and was unable to
determine scaup diet at southern latitudes; however, I did detect selection of invertebrates
at a mid-latitude site (e.g., Lake Erie). Interestingly, scaup consumed foods in proportion
to availability at the Illinois River site, yet selected for invertebrates at Lake Erie, even
though invertebrate and seed availability was similar at these sites (Table 2.1). Also
unique to the Illinois River site, I regularly observed large concentrations of scaup
foraging in unharvested cornfields soon after inundation. Considering scaup spend 3 − 4
weeks on breeding areas to acquire and maintain fat reserves before initiating RFD, and
their diets during this time consist of high-protein foods that are inefficient for building
somatic lipid (Afton and Hier 1991), the pattern I observed in scaup diet staging on the
Illinois River is what I expected to observe in spring migrating scaup (i.e., consuming
high-carbohydrate seeds to lessen their dependence on high-carbohydrate foods at
breeding areas).
Ring-necked duck. - To my knowledge, this study was the only food-selection study of
spring-migrating ring-necked ducks conducted. Previously, feeding ecology of spring-
migrating ring-necked ducks could only be inferred from pre-laying female ring-necked
ducks presumably at their breeding area in Minnesota (Hohman 1985). I found ring-
necked ducks staging in the UMR/GLR in spring 2006 consumed substantially less
99 animal matter than pre-laying female ring-necked ducks in Minnesota (Hohman 1985) at
all sites except Saginaw Bay, and either selected for seeds or consumed foods in
proportion to availability.
My data indicated spring-migrating female ring-necked ducks were heavily
dependant on seeds but may have transitioned to a diet consisting mostly of invertebrates
at northern latitudes (e.g., Saginaw Bay). Because of small sample sizes at the Wisconsin
site in 2006, however, I was unable to test these results at an additional northern latitude
site. Female ring-necked ducks typically acquire lipid reserves that are used to meet
reproductive requirements before reaching nesting areas (Hohman 1986). Therefore, it is
not surprising that I found ring-necked ducks selecting seeds at the Cache River site
during spring, as these high-carbohydrate foods are likely used to accumulate or restore
somatic lipid. Because the proportions of invertebrates and seeds available for ring-
necked ducks collected at Saginaw Bay was similar to Scioto River (approximately 50% seeds and 50% invertebrates available; see Table 2.1), yet ring-necked ducks at the Scioto
River consumed approximately twice the amount of seeds as ring-necked ducks at
Saginaw Bay, I suggest that ring-necked ducks at Saginaw Bay were in a different physiological state. It is possible that ring-necked ducks staging at Saginaw Bay during spring were in close proximity to breeding areas, perhaps explaining why I observed an increase in invertebrate consumption at this site.
100 CHAPTER 3: IMPLICATIONS FOR WETLAND MANAGEMENT FOR SPRING-MIGRATING WATERFOWL IN THE UMR/GLR
Management Implications
Unlike the diet of ducks during breeding, when all ducks depend heavily on invertebrates or during fall migration and winter when seeds and agricultural grains compose the majority of the diet of ducks, spring diet is much more variable and differs considerably among species. At least some species appear to transition to invertebrates later in spring migration, leading to intraspecific variation of diet. The variability I discovered in spring diets emphasizes the importance of providing a variety of habitats
(e.g., food types) during spring. Even though ducks are likely capable of searching for, and selecting specific food types from within their environment (see chapter 2), the variability I discovered in diet among sites and transects indicates that the ability of ducks to modify food intake is limited. Thus, food availability still plays a large role in diet, hence nutrient acquisition.
Management of wetland habitats specifically to benefit spring-migrating waterfowl is uncommon. Current wetland management practices typically intend to maximize seed (i.e., moist-soil and agricultural) abundance for fall-migrating and wintering waterfowl. Although this approach likely benefits fall-migrating and wintering waterfowl, it may not yield quality foraging habitat in spring (Greer et al. 2006). My research indicated that wetlands managed for moist-soil plant species provide important foraging habitats for some spring-migrating waterfowl (e.g., mallards, ring-necked ducks), and attract others that consume invertebrates and seeds (e.g., blue-winged teal, gadwall, lesser scaup). Thus, I recommend managers provide shallow and deep water habitats during spring with abundant moist-soil seeds and invertebrates.
101 Managing Wetlands for Invertebrates During Spring Migration
Differing water regimes will affect macroinvertebrate taxa available to foraging waterfowl. For example, Neckles et al. (2006) found that semipermanent flooding
(standing water present through the growing season) in marshes in Manitoba, Canada reduced total invertebrate densities. The taxa that were negatively impacted by semipermanent flooding are very important to foraging waterfowl (e.g., Cladocera,
Ostracoda, and Culicidae). Neckles et al. (2006) suggested that semi-permanent flooding may eliminate cues necessary for oviposition and hatch among dominant taxa. Under seasonally flooded wetlands (standing water present only through mid-summer), however, macroinvertebrate densities were not reduced, regardless of the availability of detritus. A flooding regime that would likely benefit spring-migrating and wintering waterfowl is deep-flooding impoundments that were kept flooded shallowly during winter, as these newly flooded deep wetlands will expand into previously dry habitat as water levels rise, resulting in deep habitat for diving ducks and shallow habitat for dabbling ducks (Fredrickson and Reid 1988). Conversely, wetlands that undergo spring water drawdown, likely concentrate invertebrates as they follow receding water levels and consequently improve foraging conditions for invertebrates. Gray et al. (1999) found moist-soil wetlands that were mowed during winter, rather than disked or tilled, supported diverse invertebrate communities, likely because of detritus that served as substrate for invertebrate production (Kaminski and Prince 1981). Therefore, late-winter flooding of moist-soil wetlands with mowed areas would likely benefit spring-migrating waterfowl by maximizing invertebrate abundance. Invertebrate abundance is also higher on wetlands lacking predators, such as fathead minnows and other fish (Cox et al. 1998,
102 Hornung and Foote 2006); therefore wetlands managed for waterfowl should experience complete annual drawdown and be protected from flood events that can establish such fish populations. Preventing flood events will also likely increase water clarity, hence
improving foraging conditions for ducks.
We found invertebrate production was highest in shallow palustrine forested
wetlands during spring (Schultheis, dissertation in progress). Although this habitat type
(e.g., forested wetlands) is likely inaccessible to diving ducks, it supported a diversity of
foods beneficial to spring-migrating dabbling ducks, particularly blue-winged teal that
rely heavily on invertebrate foods. Thus, forested wetland habitat should be maintained
throughout spring, particularly wetlands predominated with button-bush (Cephalanthus
sp.) and willow trees (Salix sp.) because of their high flood tolerance. Water levels in
green-tree reservoirs (GTR) (e.g., bottomland hardwood forests intentionally flooded to
produce habitat for waterfowl), in particular, should be held as long as possible to provide
rich invertebrate sources to late-migrating dabbling ducks. Because the integrity of
GTR’s depends on the survival of early successional mast-producing oak trees and these
trees are susceptible to disease when inundated during the growing season, late-winter
flooding with a pre-growing season drawdown may be beneficial to both the GTR and
spring-migrating waterfowl.
Managing Wetlands for Seeds During Spring Migration
To optimize seed abundance for spring-migrating ducks, I suggest late-winter
flooding of moist-soil wetlands at varying depths, as this wetland management practice
provides abundant seeds (Greer et al. 2006). Seed loss from depredation and
103 decomposition from inundation is minimized by a delayed flooding regime. By delaying flooding of GTR’s, not only is seed availability maximized, but survival of important mast-producing hardwood species is encouraged.
Challenges to Providing Habitat for Spring-Migrating Waterfowl
As I previously stated, I believe the greatest opportunity to manage wetland
habitats for spring-migrating waterfowl is on state and federal refuges. These, however,
are often managed to accommodate public waterfowl hunters, and delayed flooding of
these areas may meet heavy criticism from the hunting constituency. To avoid this,
wetlands could be kept at low pool during winter, still providing habitat for hunters, with
water coverage allowed to increase (newly flooding the perimeter) throughout spring.
Minimally, this strategy should be used on non-huntable wetlands that are true ‘refuges’
during winter.
Another challenge to maximizing forage availability for spring-migrating waterfowl, particularly in the Midwest, is convincing private landowners and area managers to provide wetland habitat other than flooded agricultural fields (i.e., moist-soil wetlands). While these habitats may be heavily utilized by spring-migrating waterfowl
(LaGrange and Dinsmore 1989), these food-types are lacking in important amino acids
(Buckley 1989). Additionally, water must be removed from these wetlands in early spring to prepare for planting next years crop, rendering these wetlands useless to many mid- and late-migratory species during spring. In contrast, wetlands managed for native, moist-soil plants can remain flooded without negatively impacting conditions for the subsequent year.
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113
APPENDICES
1 APPENDIX A Table A1. Aggregate percent biomass of food items in blue-winged teal collected at the Cache River study site in spring 2006 (n = 22) and 2007 (n = 27). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 2.9 3.4
Total Animal Matter 31.8 38.7
Gastropoda 4.3 17.2
Physidae 4.0 2.2
Planorbidae 0.3 15.0
Bivalvia 0.0 2.7
Spaheriidae 0.0 2.7
Chironomidae 9.8 5.2
Non-Chironomidae Dipterans 0.2 3.3
Ceratopogonidae tr. 3.2
Macrocrustacea 6.9 1.1
Amphipoda 2.6 0.1
Isopoda 4.3 1.0
Microcrustacea 4.7 tr.
Cladocera 3.1 tr.
Copepoda 0.1 tr.
Ostracoda 1.5 0.0
Annelida 4.6 0.1
Non-Dipteran Insects 1.5 8.6
Baetidae 0.0 3.7
Caenidae 0.0 2.5
Total Seed 64.9 57.8
Alisma sp. 0.0 1.9
114 Table A1 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Amaranthus sp. 4.9 2.5
Asclepias sp. 0.0 1.2
Bidens sp. 5.2 0.0
Cyperus sp. 0.8 4.5
Digitaria sp. 4.9 tr.
Echinochloa sp. 5.1 2.6
Eleocharis sp. 0.7 3.1
Eragrostis sp. 1.2 0.1
Leersia sp. 3.5 2.7
Lonicera sp. 0.0 2.1
Ludwigia sp. 0.0 17.7
Panicum sp. 10.8 3.3
Polygonum sp. 11.1 6.7
Rhynchospora sp. 2.8 0.0
Scirpus sp. 7.4 4.2
Unknown Seeds 8.0 3.1 ______
115 Table A2. Aggregate percent biomass of food items in blue-winged teal collected at the Illinois River study site in spring 2006 (n = 21) and 2007 (n = 28). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 1.1 0.2
Total Animal Matter 28.3 48.5
Gastropoda 3.2 13.3
Lymnaeidae tr. 6.7
Physidae 3.2 6.2
Planorbidae 0.0 0.3
Chironomidae 9.7 4.8
Non-Chironomidae Dipterans 0.3 2.0
Culicidae 0.3 1.7
Macrocrustacea 4.7 3.9
Amphipoda 0.9 3.1
Isopoda 3.8 0.7
Microcrustacea 1.9 7.0
Cladocera 1.9 1.3
Copepoda tr. 4.7
Annelida 0.0 6.9
Non-Dipteran Insects 7.4 8.6
Collembola 4.5 tr.
Coenagrionidae 0.0 3.5
Dytiscidae 2.8 tr.
Elmidae 0.0 1.7
Miscellaneous / Unknown 1.0 1.7
Total Seed 70.6 51.2
Amaranthus sp. 2.8 1.7
116 Table A2 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Bidens sp. 2.7 1.5
Carex sp. 0.0 6.0
Cephalanthus sp. 0.3 4.1
Cyperaceae sp. 4.8 0.0
Cyperus sp. 22.9 1.7
Digitaria sp. 0.0 4.0
Echinochloa sp. 4.3 2.0
Eleocharis sp. tr. 1.7
Eragrostis sp. 5.1 1.0
Impatiens sp. 2.0 0.0
Leersia sp. 9.9 0.8
Ludwigia sp. 0.0 2.2
Panicum sp. 0.3 3.0
Polygonum sp. 5.7 15.4
Unknown Seeds 8.8 3.0 ______
117 Table A3. Aggregate percent biomass of food items in blue-winged teal collected at the Wisconsin study site in spring 2006 (n = 15) and 2007 (n = 17). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 0.1
Total Animal Matter 31.0 51.1
Gastropoda 11.9 38.0
Lymnaeidae 5.4 33.1
Physidae tr. 1.5
Planorbidae 6.3 3.2
Chironomidae 6.7 0.5
Non-Chironomidae Dipterans 0.1 8.6
Stratiomyidae 0.1 8.3
Tipulidae 0.0 0.2
Macrocrustacea 6.7 1.4
Amphipoda tr. 0.3
Isopoda 6.7 1.0
Microcrustacea tr. tr.
Non-Dipteran Insects 0.8 0.8
Miscellaneous / Unknown 4.7 tr.
Total Seed 69.0 48.7
Alisma sp. 0.3 4.2
Amaranthus sp. 9.4 0.5
Bidens sp. 8.9 9.6
Carex sp. 0.0 4.2
Cyperus sp. 14.8 6.2
Echinochloa sp. 0.0 5.8
Leersia sp. 12.7 1.6
118 Table A3 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Polygonum sp. 17.0 1.0
Potamogeton sp. 0.0 2.5
Scirpus sp. 0.0 7.2
Solanum sp. 0.0 4.6
Unknown Seeds 6.2 0.0 ______
119 Table A4. Aggregate percent biomass of food items in blue-winged teal collected at the Scioto River study site in spring 2006 (n = 2) and 2007 (n = 10). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 6.2
Total Animal Matter 52.1 26.2
Gastropoda 44.6 2.0
Lymnaeidae 38.8 0.6
Physidae 5.9 0.5
Planorbidae 0.0 0.9
Bivalvia 0.9 0.0
Spaheriidae 0.9 0.0
Chironomidae tr. 8.5
Non-Chironomidae Dipterans 0.0 0.2
Macrocrustacea 0.0 0.1
Isopoda 0.0 0.1
Microcrustacea 0.0 10.9
Cladocera 0.0 10.9
Annelida 2.7 4.0
Non-Dipteran Insects 3.9 0.1
Hydrophilidae 3.8 0.0
Total Seed 47.9 67.5
Amaranthus sp. 0.4 tr.
Bidens sp. 47.5 0.0
Carex sp. 0.0 1.6
Echinochloa sp. 0.0 4.1
Eleocharis sp. 0.0 9.5
Leersia sp. 0.0 9.8
120 Table A4 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Panicum sp. 0.0 3.6
Polygonum sp. 0.0 16.7
Potamogeton sp. 0.0 18.2
Unknown Seeds 0.0 2.5 ______
121 Table A5. Aggregate percent biomass of food items in blue-winged teal collected at the Lake Erie study site in spring 2006 (n = 20) and 2007 (n = 6). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 22.6 31.8
Total Animal Matter 41.1 14.2
Gastropoda 35.4 12.3
Lymnaeidae 5.4 tr.
Physidae 16.4 0.9
Planorbidae 13.6 11.3
Chironomidae 1.6 0.1
Non-Chironomidae Dipterans tr. 0.4
Macrocrustacea 0.9 1.0
Amphipoda 0.3 1.0
Isopoda 0.6 0.0
Microcrustacea tr. 0.2
Annelida 1.4 0.0
Non-Dipteran Insects 1.6 tr.
Aeshnidae 0.2 0.0
Coenagrionidae 0.6 tr.
Dytiscidae 0.4 0.0
Total Seed 36.3 53.9
Cyperus sp. 0.0 11.5
Eleocharis sp. 10.1 0.0
Leersia sp. 5.3 0.0
Polygonum sp. 10.6 30.1
Scirpus sp. 6.3 9.9 ______
122 Table A6. Aggregate percent biomass of food items in blue-winged teal collected at the Saginaw Bay study site in spring 2006 (n = 11) and 2007 (n = 19). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 1.3 5.5
Total Animal Matter 65.6 55.1
Gastropoda 37.8 33.6
Lymnaeidae 7.0 12.2
Physidae 3.0 5.7
Planorbidae 27.8 15.6
Bivalvia 3.6 2.8
Sphaeriidae 3.6 2.8
Chironomidae 13.8 6.9
Non-Chironomidae Dipterans tr. 0.0
Macrocrustacea 7.8 5.1
Amphipoda 5.0 2.1
Isopoda 2.8 2.9
Non-Dipteran Insects 2.6 6.5
Caenidae 0.4 tr.
Coenagrionidae 1.2 1.0
Dytiscidae 0.0 3.7
Hydrophilidae 0.0 1.2
Phyrganeidae 0.6 0.3
Total Seed 33.1 39.2
Amaranthus sp. 11.5 tr.
Carex sp. 0.0 3.3
Cladium sp. 0.0 3.8
Cyperus sp. 0.0 5.3
123 Table A6 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Eleocharis sp. tr. 4.6
Najas sp. 0.0 1.1
Polygonum sp. 3.0 8.4
Potamogeton sp. 0.0 4.4
Scirpus sp. 8.2 4.8
Unknown Seeds 9.0 0.7 ______
124 Table A7. Aggregate percent biomass of food items in gadwall collected at the Cache River study site in spring 2006 (n = 8) and 2007 (n = 15). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 73.4 46.8
Algae 49.5 28.7
Lemna 6.6 0.0
Wolffia 17.3 0.0
Other Vegetation tr. 18.1
Total Animal Matter 5.0 18.5
Chironomidae 0.7 11.5
Non-Chironomidae Dipterans 0.2 tr.
Microcrustacea tr. 0.1
Non-Dipteran Insects 3.9 tr.
Collembola 3.8 0.0
Miscellaneous / Unknown tr. 6.6
Terrestrial Invertebrates 0.0 6.6
Total Seed 21.6 34.5
Carex sp. 4.3 0.1
Cyperus sp. 2.7 3.6
Digitaria sp. 0.0 1.5
Echinochloa sp. tr. 6.6
Eragrostis sp. 2.2 6.6
Ludwigia sp. 0.0 7.2
Panicum sp. 0.0 3.3
Polygonum sp. 4.3 4.0
Trifolium sp. 6.8 0.0 ______
125 Table A8. Aggregate percent biomass of food items in gadwall collected at the Illinois River study site in spring 2006 (n = 14) and 2007 (n = 8). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 3.0 74.4
Algae 2.2 42.4
Lemna 0.0 9.0
Other Vegetation 0.7 22.9
Total Animal Matter 6.5 21.5
Chironomidae 6.1 10.6
Microcrustacea 0.3 tr.
Annelida tr. 8.6
Oligochaeta 0.0 8.6
Non-Dipteran Insects 0.0 2.1
Coenagrionidae 0.0 0.5
Libellulidae 0.0 0.7
Corixidae 0.0 0.4
Total Seed 90.6 4.0
Amaranthus sp. 2.1 tr.
Carex sp. 13.9 0.0
Cephalanthus sp. 1.8 0.0
Cyperus sp. 40.6 tr.
Echinochloa sp. 3.8 0.1
Leersia sp. 0.0 1.5
Najas sp. 3.6 0.2
Panicum sp. 1.0 0.0
Polygonum sp. 6.3 1.5
Potamogeton sp. 3.3 0.1
126 Table A8 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Unknown Seeds 13.7 0.0 ______
127 Table A9. Aggregate percent biomass of food items in gadwall collected at the Wisconsin study site in spring 2007 (n = 16). If food items were <0.1% they were not listed. ______2007 Food Item Agg. % ______
Total Vegetation 66.1
Algae 11.7
Lemna 48.0
Other Vegetation 6.4
Total Animal Matter 2.1
Chironomidae 0.2
Non-Chironomidae Dipterans 1.4
Ceratopogonidae 0.2
Stratiomyidae 0.2
Tipulidae 0.8
Non-Dipteran Insects 0.3
Pyralidae 0.1
Total Seed 31.7
Cyperus sp. 2.6
Echinochloa sp. 2.8
Panicum sp. 7.9
Polygonum sp. 9.7
Scirpus sp. 5.9 ______
128 Table A10. Aggregate percent biomass of food items in gadwall collected at the Scioto River study site in spring 2007 (n = 1). If food items were <0.1% they were not listed. ______2007 Food Item Agg. % ______
Total Vegetation 97.6
Algae 97.6
Total Animal Matter 2.4
Chironomidae 2.4
Total Seed 0.0 ______
129 Table A11. Aggregate percent biomass of food items in gadwall collected at the Lake Erie study site in spring 2006 (n = 18) and 2007 (n = 17). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 62.9 51.4
Algae 32.6 25.5
Ceratophyllum 4.9 0.0
Chara sporangia 0.0 2.4
Myriophyllum 0.0 5.8
Lemna 24.6 5.4
Wolffia 0.6 3.2
Other Vegetation tr. 8.8
Total Animal Matter 3.9 9.8
Gastropoda 0.3 tr.
Chironomidae 0.5 1.0
Non-Chironomidae Dipterans 0.2 0.1
Macrocrustacea 0.7 1.3
Amphipoda 0.7 1.3
Microcrustacea 0.3 tr.
Annelida 0.4 tr.
Oligochaeta 0.4 tr.
Nematoda 0.8 6.4
Non-Dipteran Insects 0.6 tr.
Total Seed 33.2 38.7
Cyperus sp. 7.1 3.5
Myriophyllum sp. 2.9 0.0
Polygonum sp. 9.6 19.8
Potamogeton sp. 0.0 1.4
130 Table A11 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Scirpus sp. 6.8 11.2
Unknown Seeds 5.0 0.0 ______
131 Table A12. Aggregate percent biomass of food items in gadwall collected at the Saginaw Bay study site in spring 2006 (n = 2) and 2007 (n = 17). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 45.9 56.5
Algae 0.0 11.2
Lemna 45.9 5.8
Wolffia 0.0 1.0
Other Vegetation 0.0 38.3
Total Animal Matter 10.9 9.5
Chironomidae 9.2 7.2
Non-Chironomidae Dipterans 0.8 0.5
Empididae 0.5 0.0
Tabanidae 0.0 0.5
Tipulidae 0.3 0.0
Macrocrustacea 0.0 1.6
Amphipoda 0.0 1.6
Non-Dipteran Insects 0.9 tr.
Total Seed 43.2 33.9
Carex sp. 2.4 0.0
Eleocharis sp. 0.0 11.7
Najas sp. 30.3 0.0
Polygonum sp. 10.6 3.1
Scirpus sp. 0.0 11.8
Unknown Seeds 0.0 6.3 ______
132 Table A13. Aggregate percent biomass of food items in mallards collected at the Cache River study site in spring 2006 (n = 15) and 2007 (n = 18). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation tr. 0.0
Total Animal Matter 8.8 9.2
Gastropoda 0.4 0.1
Bivalvia 0.0 tr.
Chironomidae 0.3 2.5
Non-Chironomidae Dipterans 0.0 tr.
Macrocrustacea 0.2 0.4
Microcrustacea 0.0 tr.
Annelida 0.0 tr.
Nematoda 6.7 0.0
Non-Dipteran Insects 1.3 6.1
Naucoridae 1.3 0.0
Pyralidae 0.0 5.6
Total Seed 91.2 90.8
Carex sp. 4.5 2.5
Cephalanthus sp. 7.5 0.5
Cornus sp. 1.9 0.0
Cyperus sp. 1.7 0.7
Echinochloa sp. 2.5 8.0
Eleocharis sp. 0.5 2.1
Eragrostis sp. 0.0 1.8
Helenium sp. 8.2 0.0
Leersia sp. 14.3 1.9
Lupinus sp. 5.5 0.0
133 Table A13 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Myriophyllum sp. 1.6 0.0
Panicum sp. 7.4 tr.
Polygonum sp. 12.7 26.8
Potamogeton sp. 6.2 tr.
Rumex sp. 1.4 5.0
Scirpus sp. 7.8 tr.
Toxicodendron sp. 1.1 3.9
Unknown Seeds 5.4 2.6
Tubers 0.0 33.6 ______
134 Table A14. Aggregate percent biomass of food items in mallards collected at the Illinois River study site in spring 2006 (n = 15) and 2007 (n = 13). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation tr. 9.7
Lemna tr. 0.1
Other Vegetation 0.0 9.6
Total Animal Matter 20.1 27.5
Gastropoda 0.0 4.9
Physidae 0.0 4.6
Planorbidae 0.0 0.2
Chironomidae 6.0 13.9
Non-Chironomidae Dipterans tr. tr.
Macrocrustacea 0.0 0.1
Microcrustacea tr. 0.0
Annelida 0.0 7.5
Hirudinea 0.0 1.0
Oligochaeta 0.0 6.5
Nematoda 0.7 0.0
Non-Dipteran Insects 6.7 1.1
Baetidae 0.0 0.6
Coenagrionidae 0.0 0.3
Dytiscidae 0.0 0.2
Carabidae 6.7 0.0
Miscellaneous / Unknown 6.7 tr.
Total Agricultural Seed (Corn) 13.3 6.5
Total Non-Agricultural Seed 66.6 56.3
Amaranthus sp. 6.7 tr.
135 Table A14 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Bidens sp. 1.8 0.0
Cephalanthus sp. 0.0 0.7
Cyperus sp. 4.5 tr.
Echinochloa sp. 8.9 0.3
Eragrostis sp. 6.7 0.0
Leersia sp. 3.0 12.3
Myriophyllum sp. 0.0 1.0
Polygonum sp. 28.1 20.4
Potamogeton sp. 6.7 0.0
Vitis sp. 0.0 1.0
Unknown Seeds 0.0 4.1
Tubers 0.0 15.4 ______
136 Table A15. Aggregate percent biomass of food items in mallards collected at the Wisconsin study site in spring 2006 (n = 9) and 2007 (n = 14). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation tr. 5.6
Lemna tr. 2.2
Other Vegetation 0.0 3.4
Total Animal Matter 22.2 24.3
Gastropoda tr. tr.
Chironomidae 6.3 5.0
Non-Chironomidae Dipterans 11.0 0.3
Stratiomyidae 11.0 0.3
Macrocrustacea 4.7 10.1
Amphipoda 4.7 0.0
Isopoda 0.0 10.1
Annelida tr. 1.1
Non-Dipteran Insects tr. 7.0
Notonectidae 0.0 0.1
Leptoceridae 0.0 6.9
Miscellaneous / Unknown 0.0 0.6
Total Agricultural Seed (Corn) 10.9 0.0
Total Non-Agricultural Seed 66.8 70.0
Alisma sp. 0.0 3.0
Amaranthus sp. tr. 1.3
Bidens sp. 0.7 0.1
Carex sp. 0.0 1.0
Echinochloa sp. 0.2 tr.
Leersia sp. 26.5 7.8
137 Table A15 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Panicum sp. 0.1 0.7
Phalaris sp. 0.0 1.1
Polygonum sp. 17.4 20.0
Potamogeton sp. 0.0 2.3
Scirpus sp. 21.5 14.9
Sparganium sp. 0.0 6.9
Vitis sp. 0.0 1.4
Unknown Seeds 0.0 2.9
Tubers 0.0 5.7 ______
138 Table A16. Aggregate percent biomass of food items in mallards collected at the Scioto River study site in spring 2006 (n = 10) and 2007 (n = 20). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 8.7 3.5
Total Animal Matter 10.9 6.0
Gastropoda tr. tr.
Chironomidae 2.4 0.0
Non-Chironomidae Dipterans tr. tr.
Macrocrustacea 8.3 tr.
Amphipoda 8.3 0.0
Isopoda tr. tr.
Microcrustacea tr. 0.0
Annelida tr. 5.6
Non-Dipteran Insects tr. 0.1
Total Agricultural Seed (corn) 0.0 42.7
Total Non-Agricultural Seed 80.4 47.7
Bidens sp. 5.8 tr.
Convolvulus sp. 0.0 1.9
Echinochloa sp. 34.7 1.9
Fabaceae sp. 0.0 1.4
Leersia sp. 34.3 9.6
Polygonum sp. 2.9 8.6
Rumex sp. tr. 1.6
Setaria sp. tr. 16.3
Unknown Seeds 0.9 tr.
Tubers 0.0 4.8 ______
139 Table A17. Aggregate percent biomass of food items in mallards collected at the Lake Erie study site in spring 2006 (n = 19) and 2007 (n = 8). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 12.4 tr.
Lemna 11.4 tr.
Other Vegetation 1.0 0.0
Total Animal Matter 7.4 12.2
Gastropoda 2.8 7.7
Lymnaeidae 0.0 0.2
Physidae 2.4 5.8
Planorbidae 0.4 1.7
Chironomidae tr. tr.
Non-Chironomidae Dipterans tr. 0.0
Macrocrustacea 2.5 3.1
Amphipoda 0.9 3.1
Isopoda 1.6 0.0
Microcrustacea tr. 0.0
Annelida tr. 0.0
Non-Dipteran Insects 1.8 1.4
Caenidae 0.0 0.1
Aeshnidae tr. 0.7
Coenagrionidae 1.3 0.5
Elmidae 0.1 0.0
Hydrophilidae 0.2 0.0
Total Agricultural Seed (corn) 10.2 0.0
Total Non-Agricultural Seed 69.9 87.7
Abutilion sp. 6.6 0.0
140 Table A17 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Alisma sp. tr. 10.8
Cornus sp. 2.1 0.0
Cyperus sp. 4.8 0.7
Digitaria sp. tr. 9.0
Echinochloa sp. 9.6 12.1
Leersia sp. 11.7 16.6
Panicum sp. 2.6 6.7
Poaceae sp. tr. 6.7
Polygonum sp. 14.7 14.9
Potamogeton sp. 4.5 0.5
Scirpus sp. 0.5 8.0
Unknown Seeds 6.4 0.0
Tubers 3.4 0.0 ______
141 Table A18. Aggregate percent biomass of food items in mallards collected at the Saginaw Bay study site in spring 2006 (n = 20) and 2007 (n = 22). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 6.2 4.3
Ceratophyllum 1.2 0.0
Lemna tr. tr.
Other Vegetation 4.9 4.3
Total Animal Matter 20.4 27.0
Gastropoda 1.0 0.4
Lymnaeidae 0.1 tr.
Physidae 0.5 0.0
Planorbidae 0.4 0.4
Chironomidae 2.2 6.6
Non-Chironomidae Dipterans 0.3 0.1
Diptera puparium 0.3 0.0
Macrocrustacea 10.1 10.4
Amphipoda 2.2 4.6
Isopoda 7.9 5.8
Microcrustacea 0.2 tr.
Ostracoda 0.2 0.0
Annelida tr. 4.6
Non-Dipteran Insects 6.5 4.7
Caenidae 0.4 0.0
Coenagrionidae 0.1 0.2
Libellulidae 1.0 tr.
Gyrinidae 0.6 0.0
Hydrophilidae tr. 3.5
142 Table A18 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Limnephilidae 0.0 0.8
Phryganeidae 3.9 tr.
Total Agricultural Seed (corn) 9.9 0.0
Total Non-Agricultural Seed 63.4 68.6
Amaranthus sp. 1.3 3.2
Carex sp. 0.0 3.4
Chenopodium sp. 0.0 1.8
Cyperus sp. 0.3 0.0
Echinochloa sp. 0.1 0.1
Leersia sp. 0.0 1.0
Najas sp. 3.8 2.8
Nymphaea sp. 0.3 0.0
Polygonum sp. 6.3 4.7
Potamogeton sp. 5.5 3.4
Sagittaria sp. 3.4 0.3
Scirpus sp. 32.9 18.6
Setaria sp. 0.0 1.8
Trifolium sp. 0.0 1.7
Vallisneria sp. 0.1 tr.
Unknown Seeds 5.4 3.5
Tubers 3.6 21.3 ______
143 Table A19. Aggregate percent biomass of food items in lesser scaup collected at the Cache River study site in spring 2006 (n = 0) and 2007 (n = 2). If food items were <0.1% they were listed as trace (tr.). ______2007 Food Item Agg. % ______
Total Vegetation 0.0
Total Animal Matter 70.9
Gastropoda 6.7
Planorbidae 6.7
Bivalvia 43.1
Sphaeriidae 43.1
Macrocrustacea 21.0
Amphipoda 6.1
Isopoda 14.8
Microcrustacea tr.
Total Seed 29.1
Amaranthus sp. 0.2
Digitaria sp. 4.5
Echinochloa sp. 10.6
Leersia sp. 0.8
Ludwigia sp. 0.1
Panicum sp. 4.4
Polygonum sp. 8.2 ______
144 Table A20. Aggregate percent biomass of food items in lesser scaup collected at the Illinois River study site in spring 2006 (n = 10) and 2007 (n = 25). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 3.7
Total Animal Matter 23.1 36.9
Gastropoda 9.6 12.1
Lymnaeidae 1.4 2.6
Physidae 8.2 0.3
Planorbidae 0.0 9.2
Bivalvia 0.0 8.0
Sphaeriidae 0.0 8.0
Chironomidae 1.2 3.0
Non-Chironomidae Dipterans 0.0 tr.
Macrocrustacea 1.8 9.2
Isopoda 1.8 9.1
Microcrustacea tr. 2.5
Cladocera tr. 2.2
Annelida 10.0 1.5
Non-Dipteran Insects 0.0 0.3
Miscellaneous / Unknown 0.3 tr.
Total Agricultural Seed (corn) 0.0 15.0
Total Non-Agricultural Seed 76.9 44.3
Amaranthus sp. 13.0 0.1
Ceratophyllum sp. 0.0 2.9
Cyperus sp. 29.3 1.6
Echinochloa sp. 3.6 4.1
Leersia sp. 6.9 13.1
145 Table A20 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Myriophyllum sp. 8.3 0.0
Poaceae sp. 5.0 0.0
Polygonum sp. 6.7 14.8
Potamogeton sp. 0.0 3.9
Unknown Seeds 3.6 tr.
Tubers 0.0 1.2 ______
146 Table A21. Aggregate percent biomass of food items in lesser scaup collected at the Wisconsin study site in spring 2006 (n = 2) and 2007 (n = 5). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 0.0
Total Animal Matter 36.0 19.8
Gastropoda 0.0 1.0
Chironomidae 0.0 18.8
Non-Chironomidae Dipterans 36.0 0.0
Ceratopogonidae 1.8 0.0
Psychodidae 34.2 0.0
Total Seed 64.0 80.1
Ceratophyllum sp. 0.0 1.3
Polygonum sp. 14.0 0.0
Potamogeton sp. 0.0 78.7
Scirpus sp. 50.0 tr. ______
147 Table A22. Aggregate percent biomass of food items in lesser scaup collected at the Scioto River study site in spring 2006 (n = 1) and 2007 (n = 16). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 18.8
Lemna 0.0 13.9
Other Vegetation 0.0 4.7
Total Animal Matter 100.0 56.0
Gastropoda 0.0 1.8
Physidae 0.0 1.8
Chironomidae 0.0 41.2
Non-Chironomidae Dipterans 0.0 2.7
Chaoboridae 0.0 2.7
Microcrustacea 0.0 tr.
Annelida 100.0 2.5
Non-Dipteran Insects 0.0 7.5
Libellulidae 0.0 2.7
Hydrophilidae 0.0 4.7
Total Seed 0.0 25.2
Echinochloa sp. 0.0 6.3
Ipomoea sp. 0.0 3.0
Polygonum sp. 0.0 2.1
Potamogeton sp. 0.0 6.3
Scirpus sp. 0.0 5.7
Unknown Seeds 0.0 1.5 ______
148 Table A23. Aggregate percent biomass of food items in lesser scaup collected at the Lake Erie study site in spring 2006 (n = 20) and 2007 (n = 9). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 13.0 0.0
Algae 2.3 0.0
Other Vegetation 10.1 0.0
Total Animal Matter 48.9 50.3
Fish (Gizzard Shad) 0.0 11.0
Gastropoda 27.9 tr.
Lymnaeidae tr. 0.0
Physidae 25.2 tr.
Planorbidae 2.5 0.0
Bivalvia 0.0 8.4
Sphaeriidae 0.0 8.4
Chironomidae 9.9 21.5
Non-Chironomidae Dipterans tr. 7.4
Ceratopogonidae tr. 7.4
Macrocrustacea 1.5 0.0
Microcrustacea tr. tr.
Annelida 1.2 1.6
Non-Dipteran Insects 5.8 0.0
Collembola 1.4 0.0
Coenagrionidae 1.1 0.0
Libellulidae 2.8 0.0
Miscellaneous / Unknown 2.9 0.1
Total Seed 38.1 49.6
Abutilion sp. 2.2 0.0
149 Table A23 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Carex sp. tr. 2.5
Cyperus sp. 0.3 4.3
Ceratophyllum sp. 2.6 0.0
Echinochloa sp. 3.0 0.0
Leersia sp. tr. 1.0
Polygonaceae sp. 2.1 0.0
Polygonum sp. 5.0 24.1
Potamogeton sp. 7.7 2.2
Scirpus sp. 3.7 14.7
Unknown Seeds 11.4 0.0 ______
150 Table A24. Aggregate percent biomass of food items in lesser scaup collected at the Saginaw Bay study site in spring 2006 (n = 16) and 2007 (n = 29). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 5.6 0.1
Lemna 5.6 0.1
Total Animal Matter 68.5 89.3
Fish 0.0 7.6
Bluegill 0.0 0.7
Eurasian Round Goby 0.0 6.9
Gastropoda 6.6 15.6
Lymnaeidae 0.4 6.9
Physidae 4.0 1.6
Planorbidae 2.2 7.0
Chironomidae 57.1 44.9
Non-Chironomidae Dipterans 0.5 0.2
Chaoboridae 0.5 0.0
Macrocrustacea 0.6 6.8
Amphipoda 0.6 4.0
Isopoda 0.0 2.7
Microcrustacea tr. 3.0
Cladocera tr. 2.9
Annelida 1.0 0.0
Non-Dipteran Insects 2.5 3.5
Caenidae 1.9 tr.
Coenagrionidae 0.4 0.4
Hydrobiidae 0.0 2.7
Miscellaneous / Unknown tr. 7.5
151 Table A24 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Bryozoan 0.0 7.5
Total Seed 25.9 10.5
Ceratophyllum sp. 4.8 1.0
Chenopodium sp. 0.1 2.0
Cyperus sp. 1.8 0.3
Impatiens sp. 4.3 0.0
Polygonum sp. 0.5 1.7
Potamogeton sp. 7.9 2.6
Scirpus sp. tr. 1.5
Unknown Seeds 6.2 tr. ______
152 Table A25. Aggregate percent biomass of food items in ring-necked ducks collected at the Cache River study site in spring 2006 (n = 13) and 2007 (n = 24). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.7 7.7
Chara sporangia 0.0 3.7
Other Vegetation 0.7 3.9
Total Animal Matter 0.5 6.0
Gastropoda 0.0 4.3
Physidae 0.0 0.2
Planorbidae 0.0 4.1
Bivalvia 0.0 0.3
Chironomidae tr. 0.4
Non-Chironomidae Dipterans 0.0 0.2
Macrocrustacea 0.0 tr.
Annelida 0.0 tr.
Non-Dipteran Insects 0.4 0.7
Libellulidae 0.4 0.2
Corixidae 0.0 0.3
Total Agricultural Seed (corn) 6.9 3.9
Total Non-Agricultural Seed 92.0 82.4
Ceratophyllum sp. 0.0 5.0
Echinochloa sp. 41.3 26.0
Ludwigia sp. 0.0 8.1
Panicum sp. 38.3 3.7
Polygonum sp. 7.7 10.3
Potamogeton sp. 0.2 11.9
Scirpus sp. 0.0 2.1
153 Table A25 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Setaria sp. 2.4 0.0
Unknown Seeds 1.6 0.0
Tubers 0.0 13.9 ______
154 Table A26. Aggregate percent biomass of food items in ring-necked ducks collected at the Illinois River study site in spring 2006 (n = 11) and 2007 (n = 10). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 0.6
Total Animal Matter 9.4 9.7
Gastropoda 0.0 5.2
Physidae 0.0 5.2
Chironomidae 0.0 tr.
Macrocrustacea 9.4 tr.
Isopoda 9.4 tr.
Annelida tr. 0.0
Non-Dipteran Insects 0.0 4.3
Hydrophilidae 0.0 4.3
Total Agricultural Seed (corn) 0.0 9.4
Total Non-Agricultural Seed 90.6 80.4
Amaranthus sp. 28.3 tr.
Bidens sp. 0.0 1.0
Ceratophyllum sp. 0.0 1.1
Cyperus sp. 30.4 0.4
Echinochloa sp. 2.7 4.9
Leersia sp. 0.0 26.9
Panicum sp. 0.0 2.0
Polygonum sp. 20.3 38.6
Unknown Seeds 1.0 4.5
Tubers 7.3 0.0 ______
155 Table A27. Aggregate percent biomass of food items in ring-necked ducks collected at the Wisconsin study site in spring 2006 (n = 3) and 2007 (n = 12). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 0.0 1.4
Total Animal Matter 0.2 0.4
Chironomidae 0.0 0.4
Annelida 0.2 0.0
Total Seed 99.8 98.2
Bidens sp. 3.7 1.0
Ceratophyllum sp. 33.3 0.0
Cyperus sp. 6.3 0.0
Eleocharis sp. 8.4 0.4
Phalaris sp. 0.0 5.1
Polygonum sp. 23.3 9.9
Potamogeton sp. 24.8 66.8
Scirpus sp. 0.0 13.0
Tubers 0.0 1.1 ______
156 Table A28. Aggregate percent biomass of food items in ring-necked ducks collected at the Scioto River study site in spring 2006 (n = 7) and 2007 (n = 26). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 4.2 12.1
Chara sporangia 3.6 11.8
Other Vegetation 0.6 0.0
Total Animal Matter 12.4 27.9
Gastropoda 8.0 0.1
Physidae 7.0 tr.
Planorbidae 1.0 tr.
Chironomidae tr. 22.3
Non-Chironomidae Dipterans 0.2 0.1
Annelida tr. 4.7
Non-Dipteran Insects 4.1 0.7
Libellulidae 4.0 0.0
Total Seed 83.4 60.0
Amaranthus sp. 1.6 3.6
Cyperus sp. tr. 8.1
Echinochloa sp. 0.0 6.2
Leersia sp. 0.0 3.2
Najas sp. 41.5 0.0
Poaceae sp. 0.0 3.8
Polygonum sp. 14.4 16.2
Potamogeton sp. 11.9 15.3
Trifolium sp. 14.0 0.0
Tubers 0.0 1.0 ______
157 Table A29. Aggregate percent biomass of food items in ring-necked ducks collected at the Lake Erie study site in spring 2006 (n = 36) and 2007 (n = 25). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 9.9 9.2
Ceratophyllum 4.1 0.0
Lemna tr. 0.4
Chara sporangia 2.7 tr.
Other vegetation 3.0 8.7
Total Animal Matter 6.1 14.7
Fish 0.0 3.9
Gizzard Shad 0.0 3.9
Gastropoda 1.4 0.6
Lymnaeidae tr. 0.0
Physidae 0.7 0.6
Planorbidae 0.6 0.0
Chironomidae 1.8 5.3
Non-Chironomidae Dipterans tr. 0.0
Macrocrustacea 0.0 tr.
Annelida tr. 2.1
Non-Dipteran Insects 2.9 2.8
Coenagrionidae tr. 1.5
Phryganeidae 2.3 1.2
Total Agricultural Seed (corn) 2.7 0.0
Total Non-Agricultural Seed 81.3 76.0
Ceratophyllum sp. 0.2 1.3
Cyperus sp. 2.7 6.2
Echinochloa sp. 22.1 9.1
158 Table A29 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Leersia sp. 13.3 10.6
Myriophyllum sp. 1.3 0.0
Panicum sp. 6.1 2.5
Polygonum sp. 21.0 27.0
Potamogeton sp. 4.6 8.0
Scirpus sp. 5.5 7.5
Unknown Seeds 2.5 2.4 ______
159 Table A30. Aggregate percent biomass of food items in ring-necked ducks collected at the Saginaw Bay study site in spring 2006 (n = 15) and 2007 (n = 22). If food items were <0.1% they were listed as trace (tr.). ______2006 2007 Food Item Agg. % Agg. % ______
Total Vegetation 27.8 9.6
Lemna 1.2 tr.
Wolffia 0.0 4.2
Other Vegetation 26.6 5.3
Total Animal Matter 42.1 58.4
Gastropoda 5.5 4.1
Lymnaeidae tr. 0.2
Physidae 4.7 1.6
Planorbidae 0.5 2.2
Bivalvia 0.0 6.9
Dreissenidae 0.0 6.9
Chironomidae 35.7 18.5
Non-Chironomidae Dipterans tr. 0.0
Macrocrustacea 0.4 1.6
Amphipoda 0.4 1.5
Microcrustacea tr. 0.0
Annelida tr. 0.5
Non-Dipteran Insects 0.4 6.3
Ephemeridae 0.0 0.7
Coenagrionidae tr. 5.3
Miscellaneous / Unknown 0.0 20.6
Bryozoan 0.0 16.0
Total Seed 30.1 32.0
Amaranthus sp. 12.1 tr.
160 Table A30 continued. ______2006 2007 Food Item Agg. % Agg. % ______
Ceratophyllum sp. 8.0 4.5
Myriophyllum sp. 4.8 3.8
Najas sp. tr. 6.8
Potamogeton sp. 4.6 0.3
Scirpus sp. 0.0 6.9
Unknown Seeds 0.0 0.2
Tubers 0.0 8.9 ______
161 VITA
Graduate School Southern Illinois University
Arthur N. Hitchcock, Jr. Date of Birth: May 20, 1981
1987 Lincolnshire Blvd., Ridgeland, MS 39157
Mississippi State University Bachelor of Science, Wildlife and Fisheries Science, May 2005
Southern Illinois University Carbondale Master of Science, Zoology, December 2008
Thesis Title: Diets of Spring-Migrating Waterfowl in the Upper Mississippi River and Great Lakes Region
Major Professor: Michael W. Eichholz
162