Introduction

In many bird species, young beg for care from their parents. A parent arriving at the nest with food is met by begging nestlings, which are waving their wings, calling and stretching to expose brightly coloured gapes, all within the confines of a nest that may contain several other begging nestlings. This mode of parent–offspring communication has become a model for the study of the evolution of biological signalling.

Hungrier nestlings beg more intensely, so the parent can use the display to decide which nestling to feed and to decide how soon it should return to the nest with food (reviewed by Budden & Wright, 2001). The fact that the parent can extract information on nestling hunger from such a confusing burst of signalling raises numerous questions. How does each nestling ensure that its own signal of need is received above the din of its nestmates' displays? How do parents differentiate among these displays to choose which nestling to feed? How much do the displays, as opposed to the physical jostling toward the parent that also goes on in the nest, determine which nestlings are fed?

To answer such questions we need to understand how the begging behaviours of whole broods function together. Concepts derived from the new field of communication networks seem well suited to this task but have not yet been explicitly applied to begging. As currently defined (McGregor & Dabelsteen, 1996; McGregor & Peake, 2000), a communication network forms whenever several individuals communicate within transmission range of each other's signals.