Migration is a physiologically-demanding activity, and the ability to locate high-quality stopover habitat for refueling has major fitness implications for migrating landbirds. However, stopover habitat is being altered by human land-use changes such as introductions of exotic shrubs, and knowledge is lacking on whether or how differences in stopover habitat could impact migrating landbirds health. We first tested whether indices of fall migrant use differed between exotic-dominated and native-dominated shrublands at a stopover site in mid-Michigan through banding and fecal analyses in 2012 and 2013, focusing on gray catbirds (Dumetella carolinensis) and Swainson’s thrushes (Catharus ustulatus) (Ch. 1). Capture rate was lower in exotic shrubland than in native shrubland, and habitat switchover rate from exotic to native shrubland was greater than vice versa. Fecal analyses revealed that catbirds and thrushes selected certain native fruits. We then tested whether health status of catbirds and thrushes differed by habitat using blood collected from a subset of captured birds (Ch. 2). Plasma indices of refueling performance (fat metabolites) did not differ by habitat in either species or year, but 3 catbirds using exotic shrub had lower measures of constitutive innate immunity (only in 2013) and antioxidant capacity than conspecifics in native shrubland. Fruit nutrient and fecal data suggested that these health differences may have resulted from differential fruit consumption. This study thus provides the first evidence that differential use of stopover habitat could impact health status of migrating birds and that evaluation of stopover habitat quality using an ecophysiology approach should include immune and antioxidant measures in addition to indices of refueling performance.
Read
