Brain mass as a function of migratory distance, with extrinsic and intrinsic factors susceptible to influence the relationship incorporated as covariates.

The model is based on 74 species for which information on all variables was available. The coefficients are the slopes (continuous variables) or mean differences (binary variables) of the relationship between log-brain mass (response variable) and all the variables (predictors) estimated with the method of the phylogenetic generalized least squares and the phylogeny branch lengths set to one [57].