Big brains or big guts: Choose one

Posted on September 4, 2019

A global study compared 2,062 birds found that in highly variable environments, birds tend to have either larger or smaller brains relative to their body size. It was found that birds with relatively smaller brains tended to use ecological strategies that are not available to big-brained counterparts. Instead of relying on gray matter to survive, these birds tend to have larger bodies, eat relatively available food and make many babies.

It was further found that resident species with intermediate brain sizes are almost completely absent from high altitude (colder and more climatically variable) environments. The species that don’t go all in on either of the extreme strategies are forced to migrate to more benign climates during the winter.
Researchers further found that having large brain is typically associated with strong energetic demands and a slower life history. Free from these constraints, species with small brains can exhibit traits and lifestyles that are never seen in larger-brained ones.

As the brain is such a costly organ to develop and maintain, biologists have long been interested in understanding how large brain size – in all species could have evolved. One hypothesis is based around the idea that one of the main advantages of possessing a big brain is that it allows for higher degrees of behavioural flexibilities. Flexibilities comes with the ability to respond to different conditions – such as wide swings in temperature, or changes in food availability.

Fristoe and Botero’s new study is different as it looks at the full distribution of brain sizes across environments, allowing them to test if the different sizes are over or under-represented. Excluding contributions from migrants, the birds that live in polar or temperate environments only during more favourable times of the year – researchers found that in high altitudes, bird brain size appears to be bimodal. This morphological pattern means that bird brains are significantly larger or smaller, compared to body size.

Researchers found that small-brained species in these environments employ strategies that are unachievable with a large brain. They can persist by foraging on readily available but difficult to digest resources like dormant plant buds, the needles of conifers or even twigs. These species also have high reproductive rates, allowing their populations to recover from high mortality during challenging conditions.

Overall, brains are not evolving in isolation – they are part of a broader suite of adaptations that help organisms be successful in their lives. Given that our own specifies uses our brain to cope with these changes, it is not surprising that we exhibit a bias towards thinking about environmental variability as a force that drives the expansion of brain size.


Source material from Science Daily


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