Contests between males for burrows are common and may involve prolonged fights. The researchers wanted to explore whether the habitat (shaded or unshaded) in which territories were located affected how vigorously males defended their burrows. To do so they released an additional male with no burrow into a group of surface- active males in each habitat, watched until he initiated a fight over a burrow, and recorded time from first contact until he either took over the resident male's burrow or retreated. The researchers used a t-test to investigate whether fight duration was significantly different in the two habitats. They observed 20 fights in each of the two habitats and calculated the mean fight duration for each habitat. In shaded habitats the mean fight duration was 18.8 4.2 s compared with 6.9 1.5 s in the unshaded habitat. Using a t-test, they obtained a t value of 11.9. The critical value was 2.03 at a 0.05 level of significance (for a test with 38 degrees of freedom). What was the conclusion of this test