The diurnal activity of male and female Snow Buntings visiting their nests was studied during a period of 24 hours on 7-8 July 1982 at Disko Island (West Greenland). At the time of the observations there was continuous daylight. Females were found to visit the nest and, hence, feed the young more frequently than males and were particularly active when males spent much time singing (morning and late afternoon), A drop in activity occurred after midnight and this drop was much longer in females, which stayed at the nest for four hours, than males, which stayed on the tundra. It is argued that the activity was low when the temperatures were minimal, coinciding with the period of minimal insect activity and maximal predator presence. Social stimuli were probably responsible for the differences in activity between the sexes.