Figure 1.

Female tree swallows with experimentally enlarged broods had greater increases in baseline cort (mean ± s.e., post-manipulation cort divided by pre-manipulation cort; dark-shaded bars on left) than females with reduced broods. Additionally, females with experimentally enlarged broods had higher fitness (mean ± s.e., number of offspring fledged; light-shaded bars on right) than females with reduced or control broods. Asterisks indicate statistically significant differences among groups. Sample sizes are provided within the bars.