Contribution of wetland and crop plant foods to meet energy needs of spring-migrating waterfowl in the upper Mississippi River and Great Lakes region
Jacob N. Straub, MS
Advisor: Robert Gates
Thesis: Energetic carrying capacity of habitats used by spring-migrating waterfowl in the Upper Mississippi River and Great Lakes Region
The Upper Mississippi River and Great Lakes region (UMRGLR), including Wisconsin, Illinois, Indiana, Ohio, and Michigan, are part of an important migration corridor for >12 million waterfowl annually. Waterfowl rely on wetland and cropland habitats in the region to secure nutrients needed to complete life-history events. Wetland loss in some of these states exceeds 95% of historic levels, raising concern that food resources may be insufficient to support spring-migrating waterfowl.
The goal of this project was to improve understanding of food resource density and energy availability in wetlands and adjacent cropland habitats used by spring-migrating waterfowl in the UMRGLR. I collected plant and invertebrate food samples during two periods in spring 2006 in three wetland habitat classes (palustrine emergent, palustrine forested, lacustrine/riverine) and croplands (corn and soybean) at six study areas in the UMRGLR. I used two methods to convert food abundance to energetic carrying capacity (ECC) estimates (duck use days/ha [dud/ha]). The first method assumes constant food, habitat, and daily energy requirements (ECCu), while the second uses foraging guild- (i.e., small dabbling, grazing dabbling, omnivorous dabbling, and diving duck) specific food habits and energy requirements (ECCw). Total estimated food biomass in wetlands consisted almost entirely (>98%) of seeds, tubers, and invertebrates from benthic (substrate) samples. I failed to detect a statistically significant difference between ECCu and ECCw in 15 of 21 paired-t-test comparisons. The largest difference occurred in lacustrine/riverine wetlands in east-central Wisconsin where ECCu (59 dud/ha) was 88% below ECCw (482 dud/ha). ECCw varied among study sites (F5,504 = 14.46, P<0.001), and habitat types (F2,504 = 47.67, P<0.001) but did not differ by sampling period (F1,504 = 0.46, P = 0.500). ECCw was consistently greatest in palustrine emergent habitats (range across sites = 613 – 1,287 dud/ha), and least in lacustrine habitats (range across sites = 22 – 342 dud/ha). Cropland ECC was more variable than in wetland habitats (ranges across sites = 146- 3,303 dud/ha). Croplands had sufficient food energy to support large numbers of waterfowl but few species are capable of foraging in this habitat. Invertebrates did not contribute substantially to total food biomass or ECC for most sites and habitat types. My estimates of ECC were below what the UMRGLR Joint Venture assumes habitats provide. The greatest difference was in lacustrine habits where site-specific habitat estimates were 82-99% lower than the Joint Venture estimate. Thus, waterfowl that use lacustrine / deep water habitats may be energy-limited during spring migration in the UMRGLR.
My study examined the extent to which habitats used by spring-migrating waterfowl in the UMRGLR can provide food energy abundance. Conservation planners need reliable food abundance estimates for croplands, marshes, natural lakes, rivers, impoundments, and riparian forests that individually and collectively contribute to the total habitat resource that supports spring-migrating in the UMRGLR. My results provide a basis for understanding variation in food resource abundance along latitudinal and longitudinal gradients in the region and can strengthen the biological foundation of strategic planning of habitat conservation to achieve population goals of the North American Waterfowl Management Plan.