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16.11.2022: Do bigger heads necessarily mean bigger brains? The study of brain size (as a proxy for cognitive ability) is rather difficult in wild animals, and scientists have tried to find ways to measure brain size without harming the animals. Head size has been used in the past and seems to work for some species – but not for all. In a study on quails by Vetmeduni scientists and researchers from Poznań University of Life Sciences, Poland, researchers found that it was head height, rather than overall head volume was a better predictor of brain size, However, it turns out that every species is different and needs to be assessed separately.

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, the majority of these studies are based on comparisons between different species. A 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. To do so researchers require techniques that do not interrupt the natural life cycle of wild birds.

A first study of barn swallows proposed to use external head measurements, which require handling but not the sacrifice of the individual bird, as an accurate approximation for brain mass.

A team of researchers from the Konrad Lorenz Institute of Ethology (KLIVV) of the Vetmeduni, together with researchers from Poznań University, Poland employed this method for the first time in a small Galliform, the Common Quail. They 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.

Head height is crucial

Although the scientists found that these measurements were correlated, the correlation values were not very strong. This means that external head measurements really cannot be used reliably to predict an individual’s brain mass with high confidence. Instead, the best predictor of brain mass was not head volume per se, as was previously shown in barn swallows, but the height of the head alone.

“Our results show that the model that explained the highest proportion of variance in brain mass contained only one head measurement, the head height,” says Valeria Marasco, one of the two first authors of the study. “Nevertheless in our study species, the Common quail, this measure explained only a small proportion of the variance in brain mass of different birds. Studies on other species have found a much more significant effect of one or the other variable.”

It is likely, therefore, that other factors also explain the variation. “For example, average beak lengths in different species could influence head measurements,” says Joanna Białas, joint first author of the study. Interestingly, brain size was not at all related to body mass or length of the bird overall. Brain size has evolved from other aspects of an animal´s morphology.

The researchers 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. More studies across diverse bird species are also needed to elucidate potential relationships between relative brain size, body parameters, and sex.

The article “Are external head measurements a reliable predictor of brain size in the Common Quail (Coturnix coturnix)?” by Joanna T. Białas, Valeria Marasco, Leonida Fusani, Gianni Pola, and Marcin Tobółka was published in the Canadian Journal of Zoology.

Scientific article