By standing on the shoulders of giants, humans have built the sophisticated high-tech world we live in today. Tapping into the knowledge of previous generations—and those around us—was long thought to be a “humans-only” trait. But homing pigeons can also build collective knowledge banks, behavioral biologists have discovered, at least when it comes to finding their way back to the roost. Like humans, the birds work together and pass on information that lets them get better and better at solving problems.
“It is a really exciting development in this field,” says Christine Caldwell, a psychologist at the University of Stirling in the United Kingdom who was not involved with the work.
Researchers have admired pigeon intelligence for decades. Previous work has shown the birds are capable of everything from symbolic communication to rudimentary math. They also use a wide range of cues to find their way home, including smell, sight, sound, and magnetism. On its own, a pigeon released multiple times from the same place will even modify its navigation over time for a more optimal route home. The birds also learn specific routes from one another. Because flocks of pigeons tend to take more direct flights home than individuals, scientists have long thought some sort of “collective intelligence” is at work.
But can pigeons improve this homing ability over generations, building on the knowledge of birds that have come before? The phenomenon, known as cumulative cultural evolution, was considered “arguably unique to humans,” says Dora Biro, a behavioral biologist at the University of Oxford in the United Kingdom.
To find out if birds share this ability, Biro and Oxford biologist Takao Sasaki strapped GPS devices on homing pigeons and divided them into three groups: birds homing by themselves, birds flying with the same partner, and birds that switched up their partner every half dozen flights or so.
He and Biro based their design on the famous “spaghetti tower” test. In that experiment, one person was asked to build a tower as high as possible using raw spaghetti and clay while an observer looked on. Then, the builder left and the observer was asked to build a tower in front of a new observer. Researchers found that 10 “generations” of observers each built towers similar to the ones before them, but taller, demonstrating the basic idea of standing on the shoulders of giants.
Instead of building towers, the pigeons simply had to fly home, an instinctive behavior. Birds in all three groups improved in the first few flights home, but after that, only the group in which the most experienced bird was periodically switched out continued to get closer to the perfect route, the researchers report today in Nature Communications. The new bird in the pair was the equivalent of the observer in the spaghetti tower experiment and represented the “next generation” that learned from and built upon the experienced bird’s knowledge.
“I think the paper convincingly shows that animal groups can show both collective intelligence and cumulative culture,” says Harvard University animal behaviorist Albert Kao, who was not affiliated with the study. A naïve bird does not develop a completely new route, but instead changes an existing route that it acquires from a bird in the previous generation—and that’s a hallmark of cumulative culture, Biro adds.
Still, not everyone is convinced. “I like the paper. It is carefully—even beautifully—done, but I think this question of whether animals can and do have cumulative culture is still open,” says Claudio Tennie, a comparative psychologist at the University of Tübingen in Germany who was not involved with the work. He argues that the pigeons are not really learning a new behavior, and thus the birds demonstrate just a subtype of cumulative culture.
Maxime Derex, an evolutionary anthropologist at Arizona State University in Tempe, agrees. Cumulative culture is more complex in humans, he says. We’ve gone from the spoken to the written word and now to ever more sophisticated electronics to communicate, he notes, whereas all the birds show is that they can improve their route home.
Biro and Sasaki accept this difference between pigeons and humans. “But our study demonstrates that nonhuman animals can accumulate knowledge and improve performance over generations, satisfying the criteria for cumulative cultural evolution,” Sasaki says. “Thus, our results suggest that [this ability] may not require sophisticated cognition as previously thought.”