Introduction

Koepcke (1972), in a study of the nest sites of birds in Peruvian rainforest, describes nests in the canopy of large forest trees (lined forest-falcon, Micrastur gilvicollis), low down in thickets (hoatzin, Opisthocomus hoazin, and great antshrike, Taraba major), the ends of fine branches (sulphur-rumped flycatcher, Myiobius barbatus), and the ends of leaves (little hermit, Phaethornis longuemareus). Species belonging to four different families (Hirundinidae, Picidae, Psittacidae, Tyrannidae) were nesting in tree holes, each of characteristic location, and species of a further six families were nesting in burrows in the ground (Alcedinidae, Buccionidae, Furnariidae, Galbulidae, Hirundinidae, Momotidae), one species of quail (Odontophoridae) was nesting in cavities in the leaf litter, and a puffbird (Bucconidae) was nesting in an arboreal termite nest (Fig. 7.1). These species-typical nest sites raise questions concerning, firstly, the factors which influence nest site selection and, secondly, the adaptive significance of the properties of the chosen site. These are the questions examined in this chapter.

The use of an upwardly directed fish-eye lens showed that the nest of the warbling vireo (Vireo gilvus) in Arizona was sited so that two to four times more sky was visible through the canopy foliage in the eastern than in the western portion of the upper hemisphere. This had the effect of exposing the nest to 90% more direct sunlight in the morning than in the afternoon, apparently to reduce the thermal stress on the brood in the afternoon (Walsberg 1981).