Incidence of Invasive Privet (Ligustrum spp.) on Swainson’s Warbler Breeding Territories in the Gulf Coastal States

Gary R. Graves*

*Department of Vertebrate Zoology, MRC-116, National Museum of Natural History, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, and Center for Macroecology, Evolution, and Climate, Globe Institute, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.

Southeastern Naturalist,Volume 19, Issue 4 (2020): 627–636

Abstract
Limnothlypis swainsonii (Swainson’s Warbler) readily colonizes novel habitat formations that meet basic requirements for understory stem density and visual screening. Little is known about the warbler’s behavioral response to naturalized populations of introduced plants. I surveyed the incidence of introduced invasive Ligustrum spp. (privet) and native Arundinaria spp. (cane) on breeding territories (n = 590) of Swainson’s Warbler in the southeastern United States. Privet occurred frequently on territories in Mississippi (65.0%), Alabama (55.7%), Louisiana (52.8%), and Texas (39.5%). Territories with privet (49.6% of total) were observed in 90 counties and parishes. The survey revealed numerous instances of warbler territories located in near-monocultures of Ligustrum sinense (Chinese Privet). Territories with cane (33.1% of total) were observed in 72 counties and parishes. In a broader context, the survey data suggest that Swainson’s Warbler populations have rapidly adapted to invasive privets, which are physiognomically similar to several native thicket-forming shrubs.

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