Meeting Abstract
Physiological markers related to health are important tools in evaluating stopover habitat quality for migrating birds. Stopover habitat is being altered by land-use change such as introductions of exotic shrubs. These shrubs bear fruits that differ in nutrient composition from their native counterparts, but knowledge is lacking on how that difference impacts the health status of birds. We hypothesized that fall migrating landbirds using exotic-dominated habitat in central Michigan, USA experience poorer health, with lower fat gain, constitutive immunity, and antioxidant capacity relative to those in the native-dominated habitat. We assayed blood from two migrating species (gray catbird Dumetella carolinensis and Swainson’s thrush Catharus ustulatus) captured in native or exotic shrubland in the fall of 2012 and 2013 for triglycerides (fat gain index), total and differential leukocyte counts, activities of natural antibodies and complement, and antioxidant capacity. We found no differences by habitat in any of the measures in Swainson’s thrushes. In gray catbirds, triglycerides, total leukocyte counts, and granulocyte: lymphocyte ratio did not differ by habitat, but individuals in the exotic shrubs showed lower natural antibody activities compared to conspecifics in the native shrubs in 2013. Furthermore, antioxidant capacity of gray catbirds in the exotic shrubs was lower relative to those in the native shrubs in both 2012 and 2013. Our results indicate that while use of exotic shrubs does not impact fat gain, reduced health relative to using native shrubs could occur in some species. Studies evaluating habitat quality using physiology should measure markers of immunity and oxidative status in addition to indices of fat gain.
