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Avian Use of Purple Loosestrife Dominated Habitat Relative to Other Vegetation Types in a Lake Huron Wetland Complex

Introduction

Purple loosestrife (Lythrum salicaria) is an exotic, broad-leaved, herbaceous perennial that is common in North American freshwater wetland habitats north of 35^o N latitude (Thompson 1989). Loosestrife is native to Eurasia where it occurs in freshwater marshes, open stream margins, and alluvial floodplains; it invades similar habitats in North America (Thompson 1989). Common plant associates of loosestrife in North American wetland habitats such as cattails (Typha spp.), reed canary grass (Phalaris arundinacea), sedges (Carex spp.), and rushes (Juncus spp.) closely resemble its associates in Eurasian wetlands (Thompson et al. 1987). Loosestrife out competes and partially or completely replaces native emergent vegetation (Thompson 1989). Loosestrife often pioneers in disturbed areas such as drainage ditches (Wilcox 1995) and displaces moist-soil species such as smartweeds (Polygonum spp.) and millets (Panicum spp.) on mudflats (Thompson et al. 1987). Species of wetland plants become distributed along a wetland gradient and are good indicators of long-term hydrology and other abiotic factors (Keddy and Reznicek 1985). Wetland vegetation types generally grade from forested wetland to shrub-scrub, to wet meadow, to strand (or mudflat), to emergent marsh, and finally, to open water (Cowardin et al 1979, Keddy and Reznicek 1985). Loosestrife occupies zones near the strand including emergent and wet meadow zones.

Avian use of loosestrife is not well studied (Thompson et al. 1987). Prince and Flegel (1995) found no records in the literature of loosestrife as avian food or nesting habitat in Lake Huron wetlands. In New York wetlands, Rawinski and Malecki (1984) observed that Marsh Wrens (Cistothorus palustris) preferred cattail for nesting, whereas Red-winged Blackbirds (Agelaius phoeniceus) preferred loosestrife for nesting. Rawinski and Malecki (1984) also noted that Black-crowned Night-herons (Nycticorax nycticorax) roosted in loosestrife and Pied-billed Grebes (Podilymbus podiceps) nested in one- and two-year-old emergent loosestrife stands. Kiviat (1996) found 15 American Goldfinch (Carduelis tristis) nests in loosestrife during a 23-year study of birds in the Hudson Valley. Swift and co-workers (1988) observed Least Bitterns (Ixobrychus exilis) and other birds in Hudson River wetlands that consisted of cattail, river bulrush (Scirpus fluviatilis), loosestrife, and common reed (Phragmites australis).

Minnesota established the first statewide loosestrife control program in 1987 with the goal of broadening public awareness, conducting inventories, developing control methods, and initiating control work (Skinner et al. 1994). Minnesota has spent $US 1.75 million since the beginning of the program (Skinner, pers. comm.). Other state and federal agencies also have spent considerable money and effort to control loosestrife, in part, because wildlife values of this plant are widely regarded to be limited. Methods of control have included chemicals, water manipulation, mowing, tillage, planting robust mudflat species such as Japanese millet (Thompson 1989), and, most recently, biological control using insects (Malecki et al. 1993).

Our objective was to compare avian use of vegetation zones dominated by loosestrife with other wetland zones where loosestrife was absent or not dominant. Comparison of avian breeding species richness, density, and diversity is a necessary first step to assess the value of loosestrife-dominated habitats to birds, and ultimately to evaluate costs and benefits of loosestrife control.

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