1. Ovotransferrin is an acute-phase protein with iron-binding and immunomodulatory functions. In poultry, ovotransferrin levels increase in response to inflammation or infection, but little is known about responses in wild bird species.
2. We present a simple assay for the determination of ovotransferrin-like activity in the plasma of wild birds. The assay uses very small sample volumes, works with previously frozen plasma, is inexpensive to run, and requires only standard laboratory equipment and a spectrophotometer. Importantly, the assay does not require species-specific antibodies, making it applicable to a wide variety of species and particularly useful in comparative studies of immune function.
3. We detected significant variation in ovotransferrin concentrations among 22 bird species. Ovotransferrin concentrations were significantly repeatable among individuals, and concentrations increased significantly in response to a lipopolysaccharide challenge.
4. Within but not among species, concentrations of ovotransferrin were significantly and positively correlated with concentrations of haptoglobin, another acute-phase protein that also binds iron. Differences in concentrations of acute-phase proteins might reflect broader differences in immune strategies and responses to infection. Measuring ovotransferrin in addition to haptoglobin therefore provides fresh insights into differences in immunological defences among populations and species.
5. This assay will serve as a useful addition to the existing arsenal of field-friendly assays that have been developed for addressing questions in ecological immunology.