Brain Architecture and Social Complexity in Modern and Ancient Birds

Mark J. Burish, Hao Yuan Kueh, Samuel S.H. Wang

Research output: Contribution to journalArticlepeer-review

104 Scopus citations


Vertebrate brains vary tremendously in size, but differences in form are more subtle. To bring out functional contrasts that are independent of absolute size, we have normalized brain component sizes to whole brain volume. The set of such volume fractions is the cerebrotype of a species. Using this approach in mammals we previously identified specific associations between cerebrotype and behavioral specializations. Among primates, cerebrotypes are linked principally to enlargement of the cerebral cortex and are associated with increases in the complexity of social structure. Here we extend this analysis to include a second major vertebrate group, the birds. In birds the telencephalic volume fraction is strongly correlated with social complexity. This correlation accounts for almost half of the observed variation in telencephalic size, more than any other behavioral specialization examined, including the ability to learn song. A prominent exception to this pattern is owls, which are not social but still have very large forebrains. Interpolating the overall correlation for Archaeopteryx, an ancient bird, suggests that its social complexity was likely to have been on a par with modern domesticated chickens. Telencephalic volume fraction outperforms residuals-based measures of brain size at separating birds by social structure. Telencephalic volume fraction may be an anatomical substrate for social complexity, and perhaps cognitive ability, that can be generalized across a range of vertebrate brains, including dinosaurs.

Original languageEnglish (US)
Pages (from-to)107-124
Number of pages18
JournalBrain, Behavior and Evolution
Issue number2
StatePublished - 2004

All Science Journal Classification (ASJC) codes

  • Developmental Neuroscience
  • Behavioral Neuroscience


  • Archaeopteryx
  • Birds
  • Brain architecture
  • Cognitive
  • Machiavellian intelligence
  • Multivariate
  • Social


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