Age differences in the timing and biometrics of migrating Marsh Warblers in Kenya

Abstract

Kelsey, M. G., Backhurst, G. C. & Pearson, D. J. 1989. Age differences in the timing and biometrics of migrating Marsh Warblers in Kenya. Ring. & Migr. 10: 41–47. Marsh Warblers Acrocephalus palustris migrate southwards across East Africa during November and December on a narrow migration front. Night-time trapping of migrants attracted to powerful game-viewing lamps at Ngulia Safari Lodge in Tsavo West National Park in southeast Kenya provides a unique opportunity to study numbers of active migrants in Africa. Marsh Warblers are one of the most numerous species caught. Biometric data spanning twelve years were analysed. The passage of Marsh Warblers became increasingly dominated by first-autumn birds as the season progressed. Differences in weight between individuals appeared to be largely accounted for by differences in fat reserves rather than by wing-length (as a measure of body size). Wing-lengths decreased through the season whereas body weight and fat reserves showed no seasonal change. There was n...