Introduction

Bird reproduction has some distinctive and unusual features compared with other vertebrates. All birds lay eggs; there is not a viviparous species among them (Blackburn & Evans 1986). The eggs are also remarkably large (10–20% of body mass compared with < 3% for modern repriles) (Wesolowski 1994). About 90% of bird species show biparental care, although this is rare in other vertebrates. Parental care in most bird species also includes the construction of a distinctive nest and the incubation of the eggs (Wesolowski 1994). How these associated features of bird reproduction came about and the role of the nest in that association are the subjects of this chapter.

The nests and brood care of dinosaurs

In 1923, members of the American Museum of Natural History expedition to Mongolia discovered for the first time whole clutches of eggs laid by dinosaurs (Andrews 1932). These eggs were from the Cretaceous but clutches from the Lower Jurassic and even Upper Triassic, in what appear to be prepared nest sites, have now been described (Moratalla & Powell 1990), demonstrating that land vertebrates were constructing some sort of nest as early as 200 million years ago. Dinosaur nests are now known from sites around the world, mostly dating from the Upper Cretaceous (about 80 million years ago), but the pattern of egg laying in dinosaurs is still only known for a handful of the roughly 285 genera (Moratalla & Powell 1990).