Abstract

It is already known that unshaded, south-facing walls are not suitable for the positioning of nestboxes for Common Swifts Apus apus owing to the extreme heat from the direct sun. However, data from the Netherlands, collected over three years between May and August, have shown that temperatures in unshaded, built-in nestboxes in east- and west-facing walls can also become dangerously high. The temperature in these boxes regularly increased to more than 5oC above the ambient temperature, reaching absolute temperatures of 40oC or more on the hottest days. Such temperatures are lethal to the eggs and young in the nest. The provision of full shading is therefore essential for built-in nestboxes in south-, east- and west-facing nestboxes. Without shading, positions between northwest and northeast are the best option.