We investigated the daily and seasonal activity patterns of the White-throated Swift and related these patterns to seasonal changes in day length and variation in environmental conditions. The time of morning exit from the roost fluctuated more with daily variation in the weather than by season, occurring later after sunrise when temperatures were cool, particularly during winter. Exit time was also delayed if temperatures rapidly exceeded the optimal range for aerial insect activity shortly after sunrise. Exits were further delayed by rain. The evening return of White-throated Swifts to their roost fluctuated more predictably with season, although entry times were also influenced by weather. Entry time was delayed when temperatures were cold and occurred earlier when they were warm or hot, or during rain. The pattern of group entry varied by season. In winter, evening roost entry was clumped, with large numbers of swifts entering together. In spring, entry was more scattered, with smaller groups entering over a longer period. The pattern of morning exit was clumped year-round, with most swifts exiting together as a group.