Attendance patterns of adult Common Guillemots Uria aalge and Kittiwakes Rissa tridactyla at breeding colonies during continuous daylight were studied in arctic Norway. While there were clear diurnal variations in the attendance of Common Guillemots that were similar to those found in colonies further south, those of the Kittiwakes were more diffuse. Seasonal variations were otherwise similar to those of birds breeding further south. Variations in attendance pattern were least during incubation and early chick-rearing for both species, corroborating published recommendations of carrying out census or monitoring counts during these periods.