Perching activity was recorded in house sparrows(Passer domesticus)exposed to natural light for one year. As expected, the sparrows’ activity duration shortened to 9.6 hours in December when the days were 9.35 hours long; and the sparrows’ activity duration lengthened to 15 hours in June when the days were 15.02 hours long. In addition to this large and expected change, however, there were small changes in activity onsets, ends, and durations which depended on whether the days were lengthening or shortening. Activity onsets anticipated sunrise by 0.2 hours more when days were lengthening. The ends of activity anticipated sunset 0.2 hours more when the days were shortening. The duration of activity time (a) was 0.2 hours longer than photoperiod when the days were lengthening, but it was 0.3 hours shorter than photoperiod when the days were shortening. We made other observations: Some birds displayed a bimodal activity distribution; the duration of the heavy morning bout of activity was a function of photoperiod. Birds with early onsets tended to end their activity late. Phase of the moon and cloudiness had no effect on differences between the activity onsets and ends and the times of sunrise and sunset.