Egg colouration in Australian songbirds

Egg colouration has been a fascination for naturalists for hundreds of years. The function of egg colouration falls into two broad, non-mutually exclusive roles: signalling and structural integrity. This thesis aims to better understand the drivers of diversity in egg colouration using a phylogenetically distinct lineage, the Australian songbirds, that represents the earliest parts of passerine radiation. This aim was addressed across songbird species by mapping the evolutionary transitions of egg colour relative to the nest type they were laid in, finding evidence of correlated evolution between egg colour and nesting strategy. Egg colour diversified significantly following the shift from dome-shaped nests to open-cupped nests ca. 40 Mya. A continent-wide ecogeographical analysis was conducted to elucidate the relationships between egg colour and the environment they were laid in and found that colour was related to ecological variables in a nest-dependent manner. Life-history traits such physiology and foraging ecology were also related to egg pigment use. Results indicated that foraging ecology and diets of dome and cup nesting species differed significantly, with the latter including energy-rich fruit and nectar and higher trophic prey. Pigments were more likely to be utilised by larger-bodied birds, suggesting that shifts in nesting strategy and expansion of diets may be linked to changes in morphology. Brain sizes were investigated in relation to nest types and foraging ecology, and while no differences were found between nest types, diet breadth and composition were strongly associated with relative brain sizes. Finally, I conducted a continent-wide ecological analysis on a family of songbirds, the babblers, which perplexingly lay pigmented eggs in dome-shaped nests.