FIGURE 4.

Estimated ancestral eggshell C numbers for the 1350 avian species studied. The colour of each branch of the phylogenetic tree shows the transition in estimated C number values from the rootward node to the tipward node or the tip. The types of nest site, nest structure and nest attachment of each species are shown at tips of the phylogenetic tree. The two grey rings indicate the two major adaptive radiation events in modern bird evolution. The colours in the outermost circle indicate whether a species is a passerine or not