eWestern Birds

The Quarterly Journal of Western Field Ornithologists

Vol. 34, No. 4
December 2003
Western Field Ornithologists

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Activity Patterns of White-throated Swifts in California
Thomas P. Ryan and Charles T. Collins

ABSTRACT: 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 delayed if temperatures rapidly exceeded the optimal range for aerial insect activity shortly after sunrise. Exit times were also 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 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.

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