The influence of weather on the body mass of migrating swallowsHirundo rusticsin South Wales

Abstract

Swallows were tape lured into mist netting when coming to roost in a Phragmites swamp at a coastal site in south west Wales between July and October 1988. In total, 1214 Swallows were caught on 40 nights, and 716 were weighed and measured. A low retrap rate indicated that the day‐to‐day turnover of birds at the site was probably large. Daily changes in total catch, estimated flock size and Swallow body mass were assessed in relation to daylight weather conditions (wind speed and direction, rainfall amount and duration, temperature, sunshine) measured at a nearby meteorological station. Covariance between different weather features was small, so that their correlations with Swallow biology could be assessed separately. Estimated flock size and catch declined significantly with increasing rainfall, but more so with increasing wind speed. Wind direction had no discernible effect. Mean body mass varied by up to 14% of the overall mean (19.5 g, range of means 18.1 to 22.3 g). Although age and body size had sig...