IN THE days when milk was delivered each morning to the doorstep of almost every house in Britain, enterprising great tits sometimes learned to peck through the foil bottle-tops to get at the goodies beneath. These avian pioneers were quickly imitated by others, with the result that cream-pillaging populations emerged in several parts of the country. Cream-pillaging was one of the first recognised examples of animal culture: the transmission of behaviour from one individual to another, so that it persists down the generations. But, oddly, it was never followed up experimentally in the wild, to understand the nuances of the process.
That has just changed, with the publication in Nature of an experiment which Lucy Aplin of Oxford University conducted in nearby Wytham Wood—probably the most intensively studied habitat on the planet. Most of the great tits in this wood are known individuals, and are fitted with transponders so that they can be followed around. Dr Aplin was thus able to track in some detail how behaviour spreads, and also how tits, like people, often seem pressed into social conformity.
Wytham has several subpopulations of great tits, each living in its own neck of the wood. Dr Aplin captured two males from each of eight of these areas, to act as her initial experimental subjects. Instead of milk bottles, she and her colleagues used specially devised boxes that, if manipulated correctly, deliver a tasty mealworm to a tit. Each box has a sliding door at the front, painted blue on the left and red on the right. Opening it either way will yield a worm, but the captured tits did not know this. Those from two of the subpopulations were taught, by letting them watch how a savvy demonstrator bird did it, that sliding the door leftward was a rewarding behaviour. Those from three other subpopulations were taught to slide it rightward. Those from the remaining three parts of the wood were taught nothing, and acted as controls. The team then scattered the wood with boxes, 250 metres apart, and released the captured birds whence they had come.
In the areas where the released birds knew how to open the boxes, the others quickly learned to do so. After the boxes had been out for 20 days over the course of a month, three-quarters of the resident tits had opened a box at least once, almost always using the method introduced by the re-released males. In one of the three control areas, half managed it, by copying birds who had worked the mechanism out by trial and error. But in the other two controls, only a pitiful 9% and 31% of the tits opened a box even once.
These results suggest that, for great tits, traditions are easy to create. To find out how persistent such traditions are, Dr Aplin and her colleagues came back nine months later (a period in which, on average half the resident tits had died and been replaced by other individuals) and put some of the boxes out again. They found three things. First, enough tits in each area remembered the old days well enough to raid the boxes, thus enabling others to learn how to do so. Second, the tradition of whether to open to the left or to the right was preserved. Third, tits that had moved (as some did) from an area with a different tradition changed their behaviour to conform with local practice.
Why that should be, Dr Aplin does not know. But it suggests that, like human beings, great tits are conformists at heart.
This article appeared in the Science & technology section of the print edition under the headline "Left or right wing?"
