Pigeons in flight – lessons to be learned

Listen in on any discussion about taking a route from A to B and you’ll often hear the phrase ‘as the crow flies’. It’s meant to indicate taking the most direct route. But is that the way a crow would actually fly? It is a question that has begun to be explored, although, thus far, with pigeons rather than crows.

Dr Dora Biro, Royal Society University Research Fellow and Ernest Cook Junior Research Fellow at Somerville College, is focusing on the mechanisms and consequences of social living and social organisation in animals. One of the ways she’s doing that is by examining group decision-making and social learning in the context of navigation by homing pigeons. ‘My particular interests focus on how individuals with conflicting knowledge or preferences resolve their differences, and what information is exchanged between group members during socially mediated learning – these are fundamental questions of group living.’

Pigeons have been chosen as the focus of one element of the study because of their breeding, which has built into them an instinct to find their way ‘home’. ‘This’, says Dr Biro, ‘means a clarity of purpose in their flight – they are bred to have a particularly strong homing motivation. We can look at their behaviour, observe the mechanisms involved and rule out other motivations such as a need to stop for food, because we know that getting home is what they are trying to do.’

The work has had several phases and involves the use of high-resolution GPS tracking systems to plot in detail the routes the birds take. Commercial GPS devices are stripped down to the bare minimum necessary for them to work in order to reduce the weight the bird has to carry, and are fitted to the pigeons as tiny 17g backpacks. After a journey the backpack can then be removed and the information on it downloaded to allow researchers to plot the actual route taken. This is a significant advance on the way early work in this field was undertaken. Then, researchers had only binoculars to track the bird. They could follow the birds for as long as they remained in range, and had no information on the route they took thereafter.

Phase one was to release a group of birds one by one on what are for them relatively short journeys of, say, 25km. Dr Biro often uses a route from north Oxfordshire back to the study’s base at the University farm on the Wytham Estate. ‘The results were not what you might expect. We found that instead of taking the most direct route, many pigeons appear to follow lines in the landscape such as roads and rivers, hedgerows and railway tracks.’ But why? ‘There may be a number of factors’. says Dr Biro. ‘First, it is cognitively less demanding to follow long and stable features in the landscape rather than memorise a chain of many different landmarks. It also helps to avoid being blown off course, for example by a strong wind, if you are following a linear feature.’

This led to the second phase: releasing birds in pairs and then in groups to see what they would do then. This is the stage that had lessons for group decision-making. Says Dr Biro: ‘When there are two of you used to taking a different route you have three options: split and go your own way, go together down one or other’s route, or compromise. Being a sociable bird and feeling a safety in numbers, the pigeons tended to stick together, but the outcome depended on the pairs we chose.’

When birds with very different routes were paired, they did sometimes split. When the two routes were not that different, they flew down the middle – a route which, it emerged, was more efficient than taking either individual’s route.

In Oxford, Professor Tim Gillard leads a team of PhD students, supported by the BBSRC and Microsoft Research. In the past their work has been funded by the EPSRC, the NERC and the Leverhulme Trust. The next phase was to observe what would happen in bigger groups, with flocks of 8–10 pigeons. On this, Dr Biro collaborated with a group of statistical physicists from Eötvös University in Hungary, led by Professor Tamás Vicsek. They were interested in decision-making within the flock; which bird made a change of direction and how quickly was that followed? They found that, while most birds have a say in the decision-making, a flexible system of ‘rank’ means that some are more likely to lead and others to follow. But even the lowest birds in the hierarchy did sometimes influence the flock. Dr Biro says: ‘This dynamic, flexible segregation of individuals into leaders and followers – where even the lower-ranking members’ opinions can make a contribution – may represent a particularly efficient form of decision-making.’

Dr Biro believes that the findings could help unravel the decision-making process in other groups, including humans. ‘Our study suggests that this sophisticated leadership strategy has advantages over one based on a single leader or those in which all members contribute equally to decision-making. It is easy to see how that has implications for many aspects of our life in social groups and work-related organisations.’