IN 2015 a paper published in the Proceedings of the National Academy of Sciences reported on the personality types of people living in various London boroughs. Extroverts, the researchers who wrote it had discovered, favoured Richmond, Wandsworth and Lambeth. Those who were most open to experience clustered in Hackney and Islington. People in Barnet and Lewisham scored lower than average on emotional stability.
What this study did not address was whether someone’s home range reflects their personality traits or imposes them. In other words, is what is going on “nature” or “nurture”? However, in a piece of research just published in the Proceedings of the Royal Society, Benedikt Holtmann of Otago University, in New Zealand, and his colleagues have plugged that gap-at least, they have plugged it for dunnocks.
Personality is not a prerogative of people. Most vertebrates in which the matter has been studied show personality types of some sort. The presumption is that, in a diverse world, different personalities will best fit different social and environmental niches-exactly what seems to be happening in London.
The dunnock, known to some as the hedge sparrow, is a European bird. It has, though, been introduced to New Zealand and has thrived there. It is a well-studied species, and among the facts that have emerged about it is that individual birds do, indeed, have distinct personalities. In particular, some are measurably bolder and more tolerant of potential threats, such as nearby human beings, than others.
The team’s research area was the Botanic Garden in Dunedin, the city where the university is based. This is open to the public, but some areas are more frequented by visitors than others. Dunnocks have small territories, so it was possible to measure the amount of human disturbance in a given territory with reasonable precision. And, by ringing each of the dunnocks in the garden with colour-coded bands it was possible to identify individuals by sight. Altogether, the researchers looked at 99 of them.
They worked out a bird’s level of threat tolerance by the simple expedient of having one of their number (as far as possible the same person each time) walk towards it, and then measuring how close that individual could get before the bird flew away. They did this several times for each bird every breeding season, and repeated the process over the course of three seasons.
A particular bird’s flight distance (ie, how closely it could be approached before it departed) was, they found, constant within a breeding season. From season to season most birds got a little bolder-presumably as they learnt more about the world and what they could safely get away with. But this increase in boldness with age was small compared with the different starting points of bold and timid birds when they first arrived in a territory. It did not, therefore, much affect the fact that, on average, birds’ flight distances were inversely correlated with the level of human disturbance in their territories. This was a consequence of disturbed territories being settled by bold birds, and undisturbed territories by shy ones.
In the case of dunnocks, then, nature wins over nurture. Dr Holtmann was able to show that personalities match circumstances, rather than being created by them. Dunnocks can recognise which places suit them best, and choose to settle in them shortly after they fledge. Most likely, that is happening in London boroughs, too.