A mosaic pattern characterizes the evolution of the avian brain.

Diversity in vertebrate brain size and composition is thought to arise from either developmental constraints that cause coordinated changes between brain regions or a mosaic model, whereby changes in individual brain regions are independent of changes in other brain regions. These two mechanisms were tested in birds using multiple regression analyses. Across 13 orders, significant correlations were present between some brain regions, but not all. Most of the correlated changes reflect the connectivity between different brain components, such that regions with the most interconnections are correlated with one another but not other brain regions. Whether mosaic changes are characteristic of brain regions or systems in birds, however, to our knowledge, remains to be investigated.