Factors Influencing Measures of Immune Function in the Gray Catbird (Dumetella carolinensis) During Spring and Fall Migration

Gender, age, and migratory timing are factors that influence the lives of seasonal birds. These characteristics affect an individual’s access to resources, ability to forge, and overall stress. Acknowledging that these biological and ecological variations exist, we examined how such differences may influence certain measures of immune function in the Gray Catbird (Dumetella carolinensis) during spring and fall migration. To do this, we combined a long-term catbird study with data collected from catbirds during the fall of 2014. Then, using the latest avian molecular sexing technique, we successfully assigned gender to 30 catbirds participating in fall migration while estimating total white blood cell (WBC) counts and Haemoproteus intensity. After all the birds in this study were determined to be male, we looked for influences of age and date on these same blood parameters. We found that during spring and fall migration, younger birds had greater Haemoproteus counts and that date was negatively associated with parasite load during the spring, but positively associated with parasite load during the fall. We also found that during spring migration older birds possessed more WBCs relative to younger birds. Although we were unable to study gender, our results support the hypothesis that age and date of migration influence immune function