New research is uncovering the link between parrots’ long lives, and their big brains.
A study led by researchers at the Max Planck Institute of Animal Behavior (MPI-AB) reports that parrots’ exceptional lifespans and their remarkable cognitive abilities are traits that reinforce — or even cause — one another. These birds have surprisingly long lives for their size, in some species rivaling those of humans. That being said, their small statures would point to much shorter lives of only a few years. The longer-than-expected life expectancy has now been shown to be linked to their higher-than-expected cognitive ability, as the latter helps parrots make better use of their environments and better negotiate threats.
“The problem has been sourcing good quality data,” says Simeon Smeele, a doctoral student at the MPI-AB and lead author on the study. “Comparative life-history studies require large sample sizes to provide certainty, because many processes are a play at once and this creates a lot of variation”.
The study worked with 133,818 individual parrots across 244 species. This database, constructed in collaboration with Species360 which draws on animal records from zoos and aquaria, allowed the team to establish the first reliable estimates of the average lifespan of over half of all known parrot species. This step revealed that there is incredible diversity in the life expectancy of different parrots: some species, like the fig parrot, live between one and two years on average. Others, like the sulfur-crested cockatoo or the scarlet macaw, live an average of 25 and 30 years, respectively. Some individuals lived a maximum of 80 years, astonishingly long for a bird of their stature.
“These values are really spectacular if you consider that a human male weighs about 100 times more,” Smeele adds.
For the next step, the team used a large-scale comparative analysis algorithm to process this dataset, and determine whether each species’ cognitive abilities had an influence on their longevity. They worked with two hypotheses: first, that having larger, more capable brains allowed the birds to better handle whatever challenges they met, reducing mortality, and thus attaining longer lifespans (‘cognitive buffer hypothesis’). The second one (a mixture between the ‘expensive brain hypothesis’ and ‘delayed benefits hypothesis’) is that larger brains take more time and energy to develop, and therefore require more parental investment which slows down the overall pace of the birds’ development. As a consequence, however, the birds have more time to learn certain behaviors from their parents which help improve their life expectancy.
For this step, the team collected data on the average body weight of individual species, their relative brain to body size, and a host of developmental variables. These pieces of data were combined and used to feed computer models tailored for each hypothesis, with the team looking at which model’s output best explained the input data. The results suggest that parrots with relatively large brains compared to their overall body size (a reliable indicator of higher intelligence) were better able to solve problems in the wild that could have otherwise killed them, enabling them to live longer lives. On the other hand, factors such as diet or greater developmental costs for larger brains did not impact the average lifespan of the bird.
“This supports the idea that in general larger brains make species more flexible and allow them to live longer,” says Smeele. “For example, if they run out of their favorite food, they could learn to find something new and thus survive.”
“We would have expected the developmental path to play a more important role because in primates it is this developmental cost that explains the link between brain size and longevity”.
In the future, the team plans to investigate whether sociality and culturally learned skills can also contribute to the parrots’ long lifespans.
“One thing that makes us humans special is the vast body of socially learned skills. We are really excited to see if long-lived parrots also have a ‘childhood’ in which they have to learn everything from finding and opening nuts to avoid upsetting the dominant male. Ultimately, we would like to understand which evolutionary drivers create a species with a life history very similar to our ancestors,” Smeele concludes.
The paper “Coevolution of relative brain size and life expectancy in parrots” has been published in the journal Proceedings of the Royal Society B: Biological Sciences.