It’s not just big brains that can give birds a survival advantage in harsh urban environments. Some small-brained birds, like the ubiquitous pigeons, keep their lineage going by breeding more, European researchers have discovered.
The finding, published in the journal Frontiers in Ecology and the Environment, solves the mystery of conflicting evidence for the popular theory that birds need big brains to give them greater behavioural flexibility in coping with cities.
“We thought that maybe there was no single way to be an urban dweller,” says lead author Ferran Sayol, from the University of Gothenburg in Sweden, “and that’s what we found.”
Many birds have been driven to extinction by the world’s growing urbanisation, while others adapt and even thrive; understanding why could help improve dwindling biodiversity in cities and give insights into our feathery neighbours.
“Urbanisation represents one of the most extreme environmental threats to biodiversity and, for the majority of organisms, entails severe fitness costs, with declines in population abundances or local extinctions,” Sayol and colleagues write.
“However, for species capable of exploiting these novel environments, cities provide a potential cornucopia of opportunities, allowing increases in abundance far beyond those found in natural habitats.”
Those birds that sit on telegraph wires watching people scurrying about and grace cities with their song are exceptional, though, and could have a disproportionate influence on the health and wellbeing of city-dwelling people.
To learn their survival tactics, the researchers scoured databases and museum collections for information across 27 cities around the world on the brain (relative to body) size of 627 birds and their maximum lifespans, global distribution, migration patterns and breeding frequency.
Results confirmed that brain size played a role in urban success stories, but it depended on their reproductive strategy.
Birds that produce few broods throughout their lifetime are only successful in cities if they have a large brain. They include the American kestrel (Falco sparverius) and some tits, such as the Black-capped chickadee (Poecile atricapillus).
At the other extreme, species that have smaller brains but make lots of babies, including pigeons, mourning doves (Columbidae) and swifts (Apodidae), also do surprisingly well in cities, suggesting they prioritise their species’ future reproductive success over their current survival.
“Although relatively uncommon in nature, these trait combinations seem to be favoured in urban environments,” the authors write, “leading to a striking restructuring of avian assemblages” in cities.
The insight could help guide conservation in urban landscapes, Sayol says, particularly for birds with average brain size who are least likely to tolerate urban environments.
“For instance, if we want to increase biodiversity in urban areas, a solution could be to try to make it more green or create corridors to the neighbouring forest so then more low-breeding/small-brained species could be able to live in our cities.”