The effects of Typha x glauca invasion on wetland birds in the Great Lakes region

Project Overview
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Project Abstract: 
Wetlands provide critical habitat for many bird species of special conservation concern. Persistence of high-quality wetland habitat is necessary to maintain populations of declining wetland obligates such as American and Least Bitterns, Common Gallinule, King Rail, and Black Tern. Waterfowl (ducks, geese, and swans) rely on wetlands as migratory stopovers and brood-rearing sites. Although waterfowl numbers are generally stable, they contribute heavily to the billion-dollar migratory bird hunting industry, making them high-priority targets for conservation efforts. In Illinois, extensive draining of wetlands for agriculture has resulted in wetland obligates accounting for about 55% of all state-endangered and state-threatened bird species. Invasion by hybrid cattail (Typha × glauca, hereafter “Typha”) degrades wetland habitat quality in the Great Lakes region. Typha has become widespread due to nutrient loading from agricultural and industrial activity, as well as anthropogenic and natural hydrological disturbances. Under these conditions, dense Typha monocultures displace diverse native plant assemblages and inhibit plant germination. Typha invasion likely has an overall negative impact on wetland bird communities because it alters and homogenizes habitat structure and reduces food availability. Typha is taller and sturdier than the sedges, bulrushes, and herbs it displaces, so Typha invasion likely reduces penetrability and visibility for larger birds such as waterfowl and most herons. Mosaics of Typha interspersed with open water in a ~1:1 ratio can support waterfowl, some herons (e.g. Least Bittern), some rails (e.g. Common Gallinule), and Black Terns, but muskrat herbivory is usually required to create areas of open water within Typha stands. Furthermore, Typha-dominated wetland probably offers far fewer food resources to birds. Aquatic invertebrates have been shown to be less abundant within Typha stands than within native vegetation. Also, Typha displaces seed- and tuber-bearing plants that are important bird food sources. Birds generally avoid eating Typha seeds, and very few species eat Typha rhizomes. The objectives of Typha removal are generally to reduce Typha density and to stimulate native plant regrowth. Both objectives should hypothetically benefit birds by increasing habitat quality and food availability. Land managers may remove Typha by herbiciding, burning, or harvesting. In this study, I will assess the value of herbicide, which is a commonly-used Typha removal method, and harvesting, which is less commonly used but has the advantage of physically removing biomass, encouraging native plant germination. It is critical to determine the effects of Typha invasion on wetland bird communities, as well as the effectiveness of management efforts to reduce these effects. My research will assess the effects of Typha invasion on the availability of seeds eaten by birds, as well as the effects of Typha on bird habitat use. I plan to answer the following questions: 1) How do Typha invasion and Typha removal affect the biomass of seeds available to wetland birds? 2) How do Typha invasion and Typha removal affect wetland bird community composition? My work in Michigan will address question 2, as will the following research plan.
Project Details
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Investigator Info
Years research project active: 
2018