Male birds that exhibit 'shy' social behaviour are much more likely to join flocks of birds with a similar personality than their 'bold' male counterparts, a new study has found. But shy birds also have fewer social partners than bold birds.
The research, carried out by scientists from Oxford University and the Australian National University, used a new way of analysing the social networks that link individual animals to each other - a kind of 'Facebook for birds' - to reveal how differences between individuals underpin the way that social interactions occur across populations.
The study of great tits (Parus major) in Wytham Woods, near Oxford (UK), also found that shy male and female birds don't interact with as many different individuals as bold males or females, and that shy males and females tend to have more stable relationships than bold ones - being seen with the same individuals more often over time.
A report of the research is published in the journal Ecology Letters this week.
'Our aim in this project has been to understand why individuals differ in their social behaviour, and ultimately what consequences this has. We're increasingly realising that processes in wild populations depend in many ways on how individuals interact with each other,' said Professor Ben Sheldon, Director of the Edward Grey Institute at Oxford University's Department of Zoology, an author of the report.
'There has been a lot of work describing the range of individual personalities in the great tit,' said Lucy Aplin, a DPhil student with Oxford University and the ANU Research School of Biology, first author of the report. 'Now we are linking it to the social networks and social organisation of the species, which hasn't been done before.'
The work is part of a long-term project led by Professor Sheldon that involves tracking thousands of wild birds in Wytham Woods fitted with tiny RFID tags that can be detected by sensors on 65 feeding stations. The researchers used records of the millions of feeder visits made by birds over an entire winter to reconstruct the social network - the pattern of with whom an individual interacts and how often - across an entire population.
Aplin was part of an international research team that rated great tits on a personality axis ranging from shy to bold. Researchers tested the personality of the birds by introducing them to new environments and seeing how they would react - typically 'shy' birds would explore the strange environment very slowly whereas 'bold' ones moved quickly to explore it. The tests were repeated over time and the responses of individuals proved to be, surprisingly, very consistent so that they could be attributed a personality somewhere along the shy/bold spectrum.
The team tracked how they interacted with other birds to determine how their personality influenced social behaviour. Bold birds went for quantity over quality in their relationships, having weaker associations with more birds and foraging with several different groups.
'Measuring the social networks we could see that bolder birds tended to hop between foraging flocks and have short term foraging associations, while shy birds tended to maintain a foraging association over a long time,' said Aplin. This difference in behaviours is likely to be due to the differing responses to risk - shy birds tend to engage in low risk/low reward behaviour, whereas their bolder counterparts engage in high risk/high reward behaviour. 'Shy birds are following a social strategy where they maintain a few strong and stable social associations to minimise risk. Hopping between many flocks may increase risks for bolder birds, but might maximise rewards through improving their social position and giving them better access to information, such as the location of food.'
The research team found that similar birds - 'birds of a feather' - do indeed flock together, finding shy males most often associated with similar personalities. 'We think shy male birds might group together to avoid the more aggressive bold birds,' said Aplin, who went on to explain that females associate freely with all personalities. 'Understanding how personality is related to social network structure, in turn helps us to understand how personality and sociality evolved. We are exploring how a range of alternative social strategies could coexist in the one population,' she added.
'By uncovering the way that different types of individuals interact non-randomly, we hope to understand how this controls the way that many processes work within populations. For instance, the way that information, and disease, spread in populations depends on the structure of the social network, and our work now tells us part of the reason for that structure,' said Professor Sheldon.