What to measure to predict brain size in birds?

At least in part, the brain's capacity to process cognitive processes depends on the mass of neural tissue involved – the more tissue – the more information can be processed. In fact, studies often find a positive relationship between brain size and cognitive performance. However, majority of these studies are based on comparisons between different species. Growing number of scientists is now trying to understand how more subtle differences between individuals of the same species are related to their cognitive skills, which is often a big challenge when studying animals in nature.

A first study in the barn swallow proposed to use external head measurements, that requires handling but not the sacrifice of the study subject, as an accurate approximation for brain mass. In our research, we employed this method for the first time in a small Galliform, the Common Quail. We measured both the external head dimensions of the birds as well as the weight of their brains, and tested how well these two measurements were related to each other. Despite we did find that these measurements were correlated, the correlation values we found were not strong enough to allow using external head measurements to predict an individual's brain mass with high confidence. Moreover, the best predictor of brain mass was not head volume, as previously demonstrated in barn swallows, but the height of the head alone. We therefore recommend validating the original method of external head measurements in each avian species before making assumptions on how these measurements might be related to brain size and cognitive performance.

You can read the article here.

Joanna T. Bialas, Valeria Marasco, Leonida Fusani, Gianni Pola, and Marcin Tobolka. Are external head measurements a reliable predictor of brain size in the Common Quail (Coturnix coturnix)?. Canadian Journal of Zoology. e-First https://doi.org/10.1139/cjz-2022-0091