Cooperatively breeding vertebrates are common in unpredictable environments where the costs and benefits of providing offspring care fluctuate temporally. To balance these fitness outcomes, individuals of cooperatively breeding species often exhibit behavioral plasticity according to environmental conditions. Although individual variation in cooperative behaviors is well-studied, less is known about variation in plasticity of social behavior. Here, we examine the fitness benefits, plasticity, and repeatability of nest guarding behavior in cooperatively breeding superb starlings (Lamprotornis superbus). After demonstrating that the cumulative nest guarding performed at a nest by all breeders and helpers combined is a significant predictor of reproductive success, we model breeder and helper behavioral reaction norms to test the hypothesis that individuals invest more in guarding in favorable seasons with high rainfall. Variation in nest guarding behavior across seasons differed for individuals of different reproductive status: breeders showed plastic nest guarding behavior in response to rainfall, whereas helpers did not. Similarly, we found that individual breeders show repeatability and consistency in their nest guarding behavior while individual helpers did not. Thus, individuals with the potential to gain direct fitness benefits exhibit greater plasticity and individual-level repeatability in cooperative behavior.