FIGURE 1 The sampling of avian morphological traits over time. The number of species (above x axis) and the number of specimens (below x axis) measured for landmark studies along with their year of publication is indicated by the vertical bars. Each bar indicates the maximum number of species and specimens measured for any trait. The number of traits in each study is represented by circle sizes (continuous from 1 to 15, with examples shown in the legend). Studies openly providing raw trait data are indicated in black. AVONET contains the raw specimen-level data for Pigot et al. (2020), along with substantial expansion in coverage of both species and specimens-per-species. To provide historical context, coloured time periods correspond roughly to interest in 'ecomorphology' (blue) and 'functional traits' (red). Citations for studies not used in the main text are provided in the Supplementary Material