Full results of the relationships between distribution-based and CBC-based estimates of community composition.

For each of the four traits considered (mean mass, generation length, migratory behaviour and diet) and for all traits together, we calculated community-weighted mean trait values (CWM), functional richness (FRICH) and functional divergence (FDIV). The overall fit of the relationship between distribution-based estimates and observed community composition at the Christmas Bird Count sites was measured using a correlation test (R2 and P-values reported). Departures from a fitted relationship of y = x (i.e. a slope of 1) were assessed using a t-test (slope, t and P-values reported). For each metric the results of the strongest correlation and the smallest departure from one are shown in bold. †s indicate comparisons that were significant for these non-spatial models but that were non-significant for the spatial autoregressive models (for full spatial model results see Appendix S1).