Falls of autumn migrants : 7-9.9.76

Abstract

The number of Hirundinidae observed was clearly lower during the period in question. These birds form large feeding flocks over Buskett during the day and numbers refer to counts or estimates of these flocks. The birds feed on suspended insects carried aloft by thermals over Buskett. It is therefore reasonable to suppose that numbers at Buskett are subject to variation with weather conditions due to interference with normal migration. The low temperatures and few hours of sunlight recorded on the days in question suggest that thermal activity on these days was reduced. The observed low numbers could thus be due to either bad migration conditions or bad feeding conditions over Buskett or both.