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The night-time activity of grey-faced petrels (Pterodroma macroptera gouldi) was measured at a colony on Tiritiri Matangi Island between 27 April and 10 December 1998. Considerable seasonal variation was observed (0 to >120 birds/night). A decline in numbers of birds at the colony in early June was likely resulted from the departure of both breeding (pre-laying stage) and non-breeding birds. Another decline at the end of September was most likely a consequence of the departure of non-breeding birds only. In general, as the season progressed there were fewer petrels per night, and they arrived later. The number of birds returning to the colony increased with increasing wind speeds and birds arrived earlier when winds were stronger. High wind speeds facilitate movement between breeding and foraging grounds for this pelagic species. A sampling period of 1 h from the arrival of the 1st bird provides sufficient information to discern definite patterns in numbers throughout the year.