Credit: Tbird Ulm (CC BY-SA 3.0)
Credit: Tbird Ulm (CC BY-SA 3.0)

Scientists Instil New Cultural Traditions in Wild Tits

In the early 20th century, milkmen would deliver milk to British doorsteps, in bottles that were sealed with foil caps. Then, in the 1920s, homeowners started noticing holes in the foil. The culprits were blue tits. They had learned to peck open the bottle caps to drink the layer of cream beneath. The behaviour quickly spread. By the 1950s, it seemed that every blue tit in Britain knew the technique.

This story is now a classic tale among students of animal behaviour. It beautifully showed how a new cultural innovation—the infiltration of milk bottles—could spread among wild animals. But the tradition was well-spread before scientists noticed, which meant that they could only observe what was going on.

Lucy Aplin from the University of Oxford wanted to go one better. She wanted to do an experiment where she deliberately seeded different populations of tits with new behaviours and checked how these baby cultures spread, matured, and clashed over time.

She began in the most obvious place: Wytham Woods near Oxford. The great tits that live there have been carefully monitored since the 1940s, and they are among the best studied birds in the world. Every single individual has now been tagged with a unique microchip tag, and several antennae automatically log their movements as they fly past. These birds are subject to a degree of scrutiny that would make Orwell blush.

Into this surveillance society, Aplin introduced two new behaviours. She captured two pairs of birds from five different populations and trained them to extract food from a puzzle box, by sliding either a blue door or a red one. She then released these birds, along with untrained pairs from three other populations, back into the woods, which by then had been littered with the same puzzle boxes. These boxes could read the birds’ tags and automatically record which individuals drew near, whether they collected food, and which door-sliding technique they used. The data poured in. All Aplin had to do was wait.

After 20 days, she found that in the three populations without any trained birds, between 9 and 53 percent of the tits succeeded in opening the puzzle boxes. They had to work out how to do on their own. But among the five groups with trained demonstrators, 68 to 83 percent of the birds solved the puzzles. They were clearly learning from each other. The team proved this by recording the birds’ arrival at feeders, and working out who flocked with whom. In other words, they mapped the birds’ social network—the original Twitter. And they found that if a tit knew how to solve the puzzle, its associates were 12 times more likely to learn the technique than birds with ignorant friends.

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Proportion of birds from different populations that solved the puzzle. Red and blue lines are groups that learned to use the red and blue doors respectively. Green lines are groups without training. Credt: Aplin et al, 2014. Nature.

Aplin also found that the successful groups split into two different schools, based on what their demonstrators did. If the pioneering pair studied the red-door technique, their neighbours also used the red door. If the pioneers learned the way of the blue-door, so did their neighbours.

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Proportion of solutions that used the blue door (option A) or the red one (option B). Credit: Aplin et al, 2014. Nature.

These traditions are totally arbitrary. The blue and red doors are equally valid solutions and equally easy. But with each passing day, the birds in each population became increasingly likely to use the most popular option. They were conformists. They went with the crowd. Indeed, during the experiment, 14 birds moved to a population with a different colour preference, and 10 of them swapped to match their neighbours’ biases.

“We thought that these traditions would erode over time, but actually we saw the birds being more and more biased towards one side,” says Aplin. “I was surprised to see how persistent [the biases] were.”

That became very clear when the team revisited the birds a year later. In the intervening months, the puzzle boxes had been taken down and around 60 percent of the tits had died. The woods were full of youngsters, most of whom had never seen the puzzles before. Still, the old ways remained. The box-opening techniques spread even faster than they did in the previous year, and the red and blue-door schools stuck to their respective biases.

Several scientists have shown that cultural traditions exist among different groups of wild animals. Blue tits learn to open milk bottles; bottlenose dolphins learn to forage with sponges; humpback whales learn to catch fish with bubbles; chimps in different regions use tools in different ways.

Some groups have even done experiments with captive animals, like chimps and capuchin monkeys, to show that tutors can instil new traditions in their peers. But such experiments—the ultimate proof of cultural transmission—are much harder to do in the wild. The first of these was only published last year: Erica de Waal and Andrew Whiten from the University of St Andrews showed that wild vervet monkeys can learn arbitrary new traditions, like preferring blue corn kernels over pink ones, or vice versa. They too showed conformist tendencies: monkey see, monkey do.

Aplin’s study shows that great tits behave in the same way. “It’s a really important and very timely contribution to our understanding of cultural transmission in animals. It is done with admirable rigour, and uses a reassuring large sample of birds,” says Whiten. These kinds of studies are “steadily building a new picture of the importance of what I’ve called nature’s second inheritance system, in which behaviours are inherited not by the primary system of genetics, but instead hop from brain to brain, via learning from others.”

“We were surprised to see this behaviour, which was traditionally thought of as a complex primate one, in a bird,” says Aplin. “It suggests that animal cultures are more widespread than we might have thought.”

Joe Henrich from the University of British Columbia, who studies cultural evolution, is less surprised. We knew that great tits are good social learners, he says, and mathematical studies predicted that such species should show conformist tendencies. This new study confirms those predictions.

Aplin agrees that conformism makes sense for many animals, great tits included. “If you’re a bird coming into a new area, habitats are variable, and you don’t have a lot of info, it would be adaptive to copy what lots of locals are doing,” she says.

Reference: Aplin, Farline, Morand-Ferron, Cockburn, Thornton & Sheldon. 2014. Experimentally induced innovations lead to persistent culture via conformity in wild birds. Nature http://dx.doi.org/10.1038/nature13998