The evolution of nest site use and nest architecture in modern birds and their ancestors

Abstract

The evolution of nest site use and nest architecture in the non-avian ancestors of birds remains poorly understood because nest structures do not preserve well as fossils. Nevertheless, the evidence suggests that the earliest dinosaurs probably buried eggs below ground and covered them with soil so that heat from the substrate fuelled embryo development, while some later dinosaurs laid partially exposed clutches where adults incubated them and protected them from predators and parasites. The nests of euornithine birds-the precursors to modern birds-were probably partially open and the neornithine birds-or modern birds-were probably the first to build fully exposed nests. The shift towards smaller, open cup nests has been accompanied by shifts in reproductive traits, with female birds having one functioning ovary in contrast to the two ovaries of crocodilians and many non-avian dinosaurs. The evolutionary trend among extant birds and their ancestors has been toward the evolution of greater cognitive abilities to construct in a wider diversity of sites and providing more care for significantly fewer, increasingly altricial, offspring. The highly derived passerines reflect this pattern with many species building small, architecturally complex nests in open sites and investing significant care into altricial young. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Keywords: birds; crocodilians; dinosaurs; evolution; nest architecture; nest sites.

Figure 1.

The evolution of nest characteristics in birds and their non-avian ancestors.

Figure 2.

The fossilized remains of in situ eggs of Mesozoic birds (Neornithes) from the Late Cretaceous in Patagonia, Argentina. Reproduced with permission from Fernández et al. [55].

Figure 3.

The phylogenetic distribution of (a) nest structure, (b) nest site and (c) nest attachment among extant bird families. Filled coloured circles at the tips and nodes of the trees show nest character states in extant families and their ancestors, respectively; circles filled with multiple colours show families or ancestral taxa with multiple character states; and blue rings indicate the two major adaptive radiations in extant birds. Reproduced with permission from Fang et al. [1].

Figure 4.

Australian passerines with open and closed nests are distributed across ranges with similar (a) minimum temperatures and (b) maximum radiation levels, but species with open nests have (c) larger ranges and (d) broader niches than species with domed nests. Note that the black dots represent raw data values and the coloured dots represent average values per group. Reproduced with permission from Medina [87].