Bigger brains have led some species of parrot to live surprisingly long lives, new research shows
From: Max-Planck-Gesellschaft
March 29, 2022
Parrots are famous for
their remarkable cognitive abilities and exceptionally long lifespans. Now, a
study led by Max Planck researchers has shown that one of these traits has
likely been caused by the other. By examining 217 parrot species, the
researchers revealed that species such as the scarlet macaw and sulphur-crested
cockatoo have extremely long average lifespans, of up to 30 years, which are
usually seen only in large birds. Further, they demonstrated a possible cause
for these long lifespans: large relative brain size. The study is the first to
show a link between brain size and lifespan in parrots, suggesting that
increased cognitive ability may have helped parrots to navigate threats in
their environment and to enjoy longer lives.
Despite the fact that
parrots are well known for their long lives and complex cognition, with
lifespans and relative brain size on par with primates, it remains unknown
whether the two traits have influenced each other.
"The problem has
been sourcing good quality data," says Simeon Smeele, a doctoral student
at the Max Planck Institute of Animal Behavior (MPI-AB) and lead author on the
study, published in Proceedings of the Royal Society B.
Understanding what has driven parrot longevity is only possible by comparing
living parrots. "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," says Smeele.
To generate an adequate
sample size, scientists from the MPI-AB and the Max Planck Institute for
Evolutionary Anthropology (MPI-EvA) teamed up with Species360, which draws on
animal records from zoos and aquaria. Together, they compiled data from over
130,000 individual parrots sourced from over 1000 zoos. This database allowed
the team to gain the first reliable estimates of average life span of 217
parrot species -- representing over half of all known species.
The analysis revealed
an astonishing diversity in life expectancy, ranging from an average of two
years for the fig parrot up to an average of 30 years for the scarlet macaw.
Other long-lived species include the sulphur crested cockatoo from Australia,
which lives on average 25 years.
"Living an average
of 30 years is extremely rare in birds of this size," says Smeele who
worked closely with Lucy Aplin from MPI-AB and Mary Brooke McElreath from
MPI-EvA on the study. "Some individuals have a maximum lifespan of over 80
years, which is a respectable age even for humans. These values are really
spectacular if you consider that a human male weights about 100 times
more."
Next, the team employed
a large-scale comparative analysis to determine whether or not parrots'
renowned cognitive abilities had any influence on their longevity. They
examined two hypotheses: First, that having relatively larger brains enable
longer lifespans. In other words, smarter birds can better solve problems in
the wild, thus enjoying longer lives. Second, that relatively larger brains
take longer to grow, and therefore require longer lifespans. For each species,
they collected data on relative brain size, as well as average body weight and
developmental variables.
They then combined the
data and ran models for each hypothesis, looking at which model best explained
the data. Their results provide the first support that increased brain size has
enabled longer lifespans in parrots. Because brain size relative to body size
can be an indicator for intelligence, the findings suggest that the parrots
with relatively large brains had cognitive capabilities that allowed them to
solve problems in the wild that could otherwise kill them, and this
intelligence enabled them to live longer lives.
"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
favourite food, they could learn to find something new and thus survive."
The scientists are
surprised that factors such as diet, or the greater developmental time required
to develop larger brains, did not lead to longer average lifespans. "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," says Smeele.
In the future, the team
plan to explore if sociality and cultural learning in parrots might have also
contributed to long lifespans. Says Smeele: "Large-brained birds might
spend more time socially learning foraging techniques that have been around for
multiple generations. This increased learning period could potentially also
explain the longer life spans, as it takes more time but also makes the
foraging repertoire more adaptive."
"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."
https://www.sciencedaily.com/releases/2022/03/220329152826.htm
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