How Is Being Brainy Correlated To Longevity In Parrots?

Parrots apparently evolved larger brain sizes so they could solve problems that might otherwise have killed them, and their braininess ended up promoting their long-term survival

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Palm cockatoo (Probosciger aterrimus) at Jurong BirdPark, Singapore. This species has the largest brain in relation to body mass of any parrot alive today. (Credit: Doug Janson / CC BY-SA 3.0)

Why are parrots so long-lived? It’s an obvious question that is not well understood by the scientific community despite the fact that parrots have lived in close association with people for thousands of years.

We do know that larger animals generally live longer than smaller ones, but other factors, such as diet, latitude and sociality also affect longevity (Figure 1). But even the largest parrots are much smaller than people, yet macaws and cockatoos live as long as most people. According to new research, it turns out that longevity and brain size are closely linked: brainy birds tend to evolve long lifespans. But why?

There are three main hypotheses that may explain this relationship between a large brain and a long life. They are:

1. the Cognitive Buffer Hypothesis proposes that the greater intelligence that is typically associated with a larger brain serves to reduce the likelihood of premature death (ref). Thus, brainy individuals were more likely to survive to adulthood and to breed, thereby passing on their genes for a large brain.
2. the Expensive Brain Hypothesis suggests that an increased lifespan is an indirect result of a prolonged juvenile stage, allowing for a greater investment in building expensive brain tissues, accompanied by increased parental investment in offspring (ref).
3. the Delayed Benefits Hypothesis argues that a higher quality, skill-based diet lowers adult mortality rates and thus supports a longer juvenile period that facilitates learning from adults how to obtain a high quality diet. This extended development period allows for greater investment in brain growth and this further supports and promotes learning (ref).

F I G U R E 1. graph of the potential causal pathways that could drive parrot life expectancy. Colours represent different covariate groups. Solid lines represent assumed causal effects in all models (see above). Dashed lines represent additional causal relationships in models 2 and 3. (doi:10.1098/rspb.2021.2397)

These hypotheses are complicated and are not mutually exclusive, so more than one could be true for parrots. To test these…