Organisms have secondary sexual traits that can be beneficial, although it could also have negative effects in organism’s immune system, as the immunocompetence-handicap hypothesis proposed. In redwing blackbirds, the amount of testosterone in male birds has been shown to increase their fitness to attract female blackbirds; however, do higher testosterone level compromises their immune-competence? I hypothesized that testosterone level has no effect on blackbirds’ immune system. This was tested by comparing the before and after antibody levels of thirteen male blackbirds that were embedded with small permeable testosterone-filled tube. The differences in the antibody levels between before and after testosterone level, were found to be normally
