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. (b) What was the null hypothesis for this test