Mixed associations between Hemlock decline and Louisiana Waterthrush habitat selection and fitness in Tennessee

Eastern Hemlock (Tsuga canadensis) is declining throughout the eastern United States due to the invasive Hemlock Woolly Adelgid (Adelges tsugae). In the southern Appalachians, hemlock is concentrated in moist ravines and its decline threatens riparian ecosystems. Directly related to birds, the majority of research on this invasion has examined changes in avian community diversity and few studies have evaluated a single species’ response to hemlock-decline induced habitat changes. The Louisiana Waterthrush (Parkesia motacilla; LOWA) is an obligate riparian species that could be sensitive to hemlock condition in the southern Appalachians. LOWA are known to adjust behaviorally to other anthropogenic-based environmental changes such as habitat fragmentation and stream acidification, but how they respond to hemlock decline is currently unclear. Our preliminary analysis suggests that within-territory habitat selection was not related to hemlock condition and it was not associated with LOWA foraging area selection. However, nest site selection was related to hemlock decline via an interaction with another habitat characteristic (percent ground cover of live tree boles). Nest survival was lower in areas where mixed hardwood species dominated the understory, suggesting that hemlock decline could indirectly impact LOWA fitness dependent on riparian habitat succession subsequent to local hemlock loss. In total, our results indicate that the consequences of hemlock decline for this charismatic riparian species in Great Smoky Mountains National Park are likely complicated and dynamic. Adult LOWA may be able to adjust their foraging behavior following hemlock decline-induced habitat changes; however, hemlock decline could have negative consequences on reproduction.