ORIGINAL ARTICLE Effects of Japanese Knotweed on avian diversity and function in riparian habitats L. Tucker Serniak 1,2 • Clay E. Corbin 1 • Amber L. Pitt 3 • Steven T. Rier 1 Received: 12 November 2015 / Revised: 6 May 2016 / Accepted: 29 August 2016 Ó Dt. Ornithologen-Gesellschaft e.V. 2016 Abstract The impacts of the invasive plant Japanese Knotweed (Fallopia japonica) on native plant and inver- tebrate communities in its introduced range have been relatively well studied, and studies have revealed pre- dominantly negative impacts. However, little research has focused on the impact of knotweed on higher trophic levels. This study investigated how riparian bird commu- nities respond to different levels of knotweed invasion. Birds were counted in 21 fixed-width transects located along ten streams in Pennsylvania, a prime avian breeding area, winter roosting site, and migratory staging area located along the Atlantic Migratory Flyway. Species richness and overall abundances did not significantly differ between levels of knotweed coverage. However, three species exhibited significant positive correlations with knotweed cover, and one species exhibited a significant negative correlation. Species and foraging guild composi- tion differed between survey locations with and without knotweed. Species frequently found around human habi- tation and in degraded habitats were associated with knotweed, while more sensitive species were associated with native vegetation. Locations with knotweed were also associated with fewer foraging guilds and lacked an asso- ciation with shoreline gleaners, water ambushers, and ground foragers, indicating a potential loss of ecological function. Given the widespread distribution of Japanese Knotweed, management actions to reduce or eliminate knotweed from riparian corridors are necessary in order to preserve avian diversity and function. Keywords Biological invasions Á Fallopia japonica Á Functional diversity Á Japanese Knotweed Á Species diversity Zusammenfassung Die Folgen von Japanischem Kno ¨terich fu ¨r die orni- thologische Vielfalt und die Funktion von Flussuferha- bitaten Die Auswirkungen von Japanischem Kno ¨terich (Fallopia japonica) auf die heimischen Pflanzen- und Wirbellosen- gemeinschaften in Gebieten, in denen diese invasive Pflanzenart eingeschleppt wurde, sind relativ gut unter- sucht, und Studien belegen u ¨berwiegend negative Effekte. Allerdings haben sich bislang nur wenige Forscher mit Auswirkungen von Kno ¨terich auf ho ¨here Trophiestufen bescha ¨ftigt. In dieser Studie untersuchten wir, wie Vogel- gemeinschaften der Flussufer auf unterschiedlich starkes Vordringen von Kno ¨terich reagieren. Es wurden Vogelza ¨hlungen in 21 Transekten fester Breite entlang von zehn Flu ¨ssen in Pennsylvania durchgefu ¨hrt, einem wichti- gen Brut- und U ¨ berwinterungsgebiet sowie Versamm- lungsplatz fu ¨r Zugvo ¨gel entlang des Atlantischen Zugkorridors. Artenvielfalt und Gesamtha ¨ufigkeiten unterschieden sich nicht signifikant zwischen verschiede- nen Graden der Kno ¨terichbedeckung. Allerdings wiesen Communicated by C. G. Guglielmo. & L. Tucker Serniak tuckerli@oregonstate.edu 1 Department of Biological and Allied Health Sciences, Bloomsburg University of Pennsylvania, 400 East Second Street, Bloomsburg, PA 17815, USA 2 Present Address: Environmental Sciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331, USA 3 Environmental Science Program and Department of Biology, Trinity College, 300 Summit Street, Hartford, CT 06106, USA 123 J Ornithol DOI 10.1007/s10336-016-1387-6