alongside his official tasks, mills took an interest in ornithology, gathering information for the bombay natural history society, and in ethnography. he published a number of monographs on naga peoples in the 1920s, and in 1930 was named honorary director of ethnography for assam. the same year he married pamela moira vesey-fitzgerald. in 1943 he was appointed adviser to the governor of assam for tribal areas and states.