Removal of an invasive wetland grass (Phragmites australis) increases the quantity of emerging invertebrates and avian aerial foraging activity

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Courtney Robichaud, Rebecca Rooney

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Invasive Phragmites australis subsp. australis (European Common Reed) is now found throughout North America. Phragmites australis displaces resident vegetation and replaces it with tall, dense stands that negatively alter wetlands. To contend with invasion, the Ontario government began a project to control P. australis and restore native vegetation diversity in Long Point, ON, a peninsula located on the north shore of Lake Erie, by aerially applying glyphosate-based herbicide. Since Long Point is ecologically significant and a regional biodiversity hotspot, we wanted to assess how restoration influenced its ecological function and habitat value for species at risk. In particular, we quantified the amount and quality of emerging invertebrates (secondary production) and the foraging activity of aerial insectivore birds (i.e. swallows), including Barn Swallows (Hirundo rustica), which are classified as threatened in Ontario. We paired point-count surveys with emergence traps in 2017 and 2018 in herbicide-treated marsh habitat, invaded (P. australis) habitat, and resident (i.e. meadow marsh, cattail marsh) habitat. Preliminary data indicates that twice as many invertebrates are emerging from herbicide-treated habitat compared to other habitat types. Further, total aerial insectivore abundance was 54.5% higher in herbicide-treated habitat and 35.5% higher in resident habitat compared to invaded habitat. Barn Swallow specifically preferred herbicide-treated habitat, as abundance was 123% higher compared to invaded habitat. We conclude that efforts to eradicate invasive P. australis and restore wetland vegetation provide improved foraging habitat for at-risk aerial insectivore birds, most likely by increasing the quantity of invertebrate prey.

Resource Type:
Conference Presentation, SER2021

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