Group size predicts brain size in primates and some other mammal groups, but no such relationship has been found in birds. Instead, stable pair-bonding and bi-parental care have been identified as correlates of larger brains in birds. We investigated the relationship between brain size and social system within the family Picidae, using phylogenetically controlled regression analysis. We found no specific effect of duration or strength of pair-bonds, but brain sizes were systematically smaller in species living in long-lasting social groups of larger sizes. Group-living may only present a cognitive challenge in groups in which members have individually competitive relationships; we therefore propose that groups functioning for cooperative benefit may allow disinvestment in expensive brain tissue.
Electronic supplementary material is available online at http://dx.doi.org/10.6084/m9.figshare.c.3702202.
- Received January 5, 2017.
- Accepted February 15, 2017.
- © 2017 The Author(s)
Published by the Royal Society. All rights reserved.