Long-term effects of a Phragmites australis invasion on birds in a Lake Erie coastal marsh

On the North shore of Lake Erie, Long Point provides habitat to many thousands of breeding and migrating birds, including marsh-nesting species that are in decline across the Great Lakes. Invasive Phragmites australis threatens the ecological integrity of these marshes. Early concerns prompted a study into the effects of invasion on bird use in 2001-2002 that concluded P. australis was not a major bird conservation issue. We evaluate breeding season bird occupancy in these wetlands after over a decade of P. australis expansion, comparing bird diversity and abundance in P. australis with diversity and abundance in the vegetation communities that P. australis is displacing: cattail, meadow, and open-water marsh. We also examine community composition and functional traits to better capture the effects of P. australis invasion. In 2015, total bird abundance was lower in P. australis than cattail marsh (ANOVA p < 0.001), with little difference in bird species richness among vegetation types (ANOVA p = 0.272). Bird community composition was distinct among the vegetation types (MRPP p < 0.001), such that P. australis supported a subset of bird species found within cattail and meadow marsh habitat, rather than novel species. Phragmites australis habitat excludes many marsh-nesting species and provides habitat for shrub-nesting, ground and foliage gleaners instead. Marsh-nesters of conservation concern are restricted to remaining cattail, meadow marsh, and open-water habitat. The full effects of P. australis invasion may exhibit a lag time, and community composition and functional traits should be considered when evaluating the effects of biological invasions.