More than 160 hours observations on the territorial behaviour of the broad-billed rollers were made in the West Tianmu Mountain, Zhejiang Province, from April to August, 1981.Activity Frequency (A. F. = mean times of flying, a pair perhour) was suggested as an index to quantitate the varying amount of flying activities of the birds. (1) The A. F. variation during the whole breeding cycle was characterized by a "U" shaped curve. (2) When territories were first established, the A. F. value got to its top of t...