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’.

The evolutionary ecology of nests: a cross-taxon approach

“…The evolution of nest architecture and nest sites in birds and their non-avian ancestors is reviewed by Mainwaring et al . [ 50 ] and they highlight a trend of nests being located in increasingly exposed locations. There has also been a pattern towards nests becoming less substantial yet increasingly elaborate, particularly in passerine birds, which has been accompanied by parents laying fewer eggs and providing an increasing amount of time per offspring over evolutionary timescales [ 50 ].…”

Plumage and eggshell colouration covary with the level of sex-specific parental contributions to nest building in birds

“…Higher quality oviparous individuals may also be expected to invest more heavily in laying colourful eggs (Moreno and Osorno 2003 ) together with costs associated with other aspects of parental care, including nest building (Mainwaring and Hartley 2013 ; Cuthill et al 2017 ). Calcareous reptilian eggs were thought to be white, but as dinosaurs, and birds, evolved to breed in more exposed locations, they laid more pigmented eggs for camouflage, mimicry, or individual recognition (Kilner 2006 ; Wiemann et al 2018 ; Mainwaring et al 2023 ). In extant birds, meanwhile, white eggs are typically laid by species breeding in relatively safe locations (e.g.…”

“…cavities), whilst species occupying more vulnerable nest sites (e.g. open nests) often lay visually cryptic, brown eggs that are maculated (Kilner 2006 ; Mainwaring et al 2015 , 2023 ).…”