Swainson's Warbler Breeding Distribution and Habitat Characteristics in Bottomland Hardwood Forests of the Lower Piedmont in North Carolina: Importance of Chinese Privet

Abstract

The Piedmont physiographic province in southeastern North America generally comprises a large gap between low montane and Coastal Plain breeding populations of Limnothlypis swainsonii (Swainson's Warbler). I conducted land-based surveys of singing males during spring 2017–2018 in late-successional bottomland hardwood forests along and adjacent to accessible areas of the Great Pee Dee River in the Lower Piedmont of Anson and Richmond counties, NC. I located 38–41 territorial males each year and in 2018 measured 12 territories where birds were present both years. Arundinaria spp. (cane) culm counts among the 4 shrub subplots across all plots were low (median = 694/ha), and cane was absent from half of the 12 plots. In contrast, the dense understory within bottomland hardwood forests occupied by Swainson's Warblers was generally dominated by Ligustrum sinense (Chinese Privet). Chinese Privet was present in all plots and had high understory-stem counts (median = 32,539/ha), 55% of the total of the median of all small woody stems and cane culm counts (59,325/ha). Despite the replacement of native shrubs and cane by the riparian invasive Chinese Privet, this latter median count exceeds the recommended minimum count of understory-stems and culms (∼40,000/ha) for Swainson's Warbler breeding territories. This is the first study to document anywhere within Swainson's Warbler breeding range that Chinese Privet constitutes the most important habitat characteristic in bottomland hardwood forests. This study is also the first anywhere within the Piedmont to document that Swainson's Warbler is locally fairly common at the edge of their range along the Great Pee Dee River of North Carolina.