How did Kettlewell directly study the moths?

Kettlewell conducted his studies by releasing both light and dark-colored moths in different environments, primarily in the English countryside. He observed the survival rates of these moths against natural predators, particularly birds, in varying backgrounds, such as light-colored lichen on trees versus darker soot-covered surfaces. By marking the moths and recapturing them, he was able to gather data on which color variant was better camouflaged and thus had a higher survival rate, providing evidence for natural selection in action.