Island birds would likely beat their mainland relatives in a battle of wits
Life on a tropical island may seem tranquil. But for some birds, the treacherous storms and isolation force them to evolve bigger brains and crafty behaviour.
Tourists flock to tropical islands for sandy beaches, calm waves and fun in the sun. On occasion though, oceanic islands get hit with devastating hurricanes, tsunamis and other storms that can wipe out vegetation.
Erratic island test tube
For island birds, the unpredictable environment often forces them to adapt or die — a natural laboratory for biologists studying evolution.
Islands are like test tubes for evolution, said Prof. Andrew Iwaniuk, who holds the Canada Research Chair in comparative neuroanatomy in the department of neuroscience at the University of Lethbridge.
"You can kind of think of this as the bird equivalent of the reality show Survivor. They're all trapped there. They all have to eke out an existence and aren't able to leave," Iwaniuk said.
Now, Iwaniuk and researchers from Spain and Sweden have confirmed a connection between brain size in birds living on islands compared with their mainland counterparts: island birds are often brainer.
A key question they explored was does moving to an island cause an increase in brain size or are larger brained birds better able to survive on islands in the first place?
To find out, Iwaniuk toured through different museums across the globe measuring the inside of skulls to estimate the brain size of nearly 2,000 bird species.
"We've found that it's actually the birds are moving to these islands and once on the islands they evolve these relatively larger brains."
Now, there are trade-offs to evolving a bigger brain. And the first bird feature to go is often a defining one — flight.
Birds that fly to islands tend to weaken or ditch the ability to fly over evolutionary time because their habitat tends to be sparse in predators like weasels or even hawks. (Large predators often don't have enough land or prey on islands to survive, biologists say.)
Iwaniuk pointed to two traits that favoured island birds:
- Innovation such as tool use.
The Barbados bullfinch shows resourcefulness in spades. As Prof. Louis Lefebre at McGill University in Montreal showed, wild Barbados bullfinch learned to steal sugar packets from cafes and open them up to access a food resource that other birds can't.
You can kind of think of this as the bird equivalent of the reality show Survivor. They're all trapped there. They all have to eke out an existence and aren't able to leave.- Andrew Iwaniuk
For innovation, the New Caledonian crow is a master at making and using tools that it carries around the island to access food. Iwaniuk said researchers have found the crow clips leaves off a type of palm tree and then cuts notches in it to stick in holes to drag out insects. (Chimpanzees show a similar use of tools.)
"Relatively larger brains are largely driven by the expansion of a region that we refer to as the pallium. The pallium is part of the avian brain that you can think of being equivalent to the cortex in the human brain. So this is really the thinking and decision-making part of the nervous system," Iwaniuk said.
Put eggs in one basket
Birds that have evolved on islands also "do things on island time," he said. They tend to have smaller clutches and larger eggs as they invest more resources in individual offspring.
"It actually takes longer for them to fledge or leave the nest. They're dependent on their parents for a longer period of time. And we know that that is in itself already associated with having a relatively large brain."
Often, larger brained birds such as parrots and corvids like jays, magpies and ravens, got even brainier once they were on islands, the researchers found.
But there were also exceptions. The brain size of ducks and other wildfowl were largely the same whether they lived on islands in the ocean or on the mainland.
In their study, the scientists also looked at factors such as the breadth of what the birds ate and how much their habitat varied from year to year.
Some chirps in this soundscape were provided under Creative Commons by Xeno-canto, a citizen-science project collecting and annotating birdsongs and calls.