Introduction

The ground nesting blackstart (Cercomela melanura) is one of a number of species of mostly desert birds of several families that build a rampart of small stones at the entrance of the sheltered nest. Leader and Yom-Tov (1998), on the basis of artificial nest predation experiments, conclude this is to give incubating females early warning of the approach of nest predators and so save themselves. Stones are not a common nest building material, but they have the properties required for this defensive role.

Chapter 4 makes a case for the use of specific materials for constructional reasons, in particular allowing the behavioural repertoire to be kept simple, even stereotyped. However, uniformity in the choice of materials may also improve structural integrity. Uniformity of composition or standard building units should tend to eliminate points of weakness in the structure. This argument applies only to those parts of the nest that have an important structural role, but nests are differentiated structures; stones appear to be specifically chosen by the blackstart for a defensive role in the nest. So, there is also an argument for nest material specialisation on the grounds that the material chosen is the best available one for the job, structural or otherwise.

Nests perform a variety of functions under the general heading of protecting the eggs and young, different parts having different roles.