Lewis Wolpert: 'Many pigeons prefer to fly following roads'
Wednesday 06 October 2004
How good is your sense of direction? Having been taken by car some 20 miles, could you easily find your way back home if you then had to drive?
How good is your sense of direction? Having been taken by car some 20 miles, could you easily find your way back home if you then had to drive? Could you do as well as pigeons? Their homing ability relies, it is thought, on a map and compass mechanism that involves an internal clock and a compass direction related to the sun. Butrecent work has shown that this is not enough, and that they must also have a large-scale mental map which gives them information about their current position in relation to their loft. What this mechanism might be is controversial, and both use of the earth's magnetic field and gradients in the air that can be detected by smell, have been proposed. There is also the problem that the birds do not fly directly home according to a a straight compass route.
But it is generally agreed that vision could play an important role, particularly when they are just a few miles from their loft; when further away the role of vision is controversial. This is the issue which new research has tried to resolve. A European group of scientists have used a small global positioning system which is attached to the back of each pigeon and records in detail the entire route taken by the pigeons as they fly home. It is accurate in recording the position of a bird every second to about 20 feet.
Over a period of three years, 216 tracks of 34 birds were analysed. All the pigeons were pre-trained from sites near the west coast of Italy. The experienced pigeons oriented themselves homewards on release, no matter where they were released. Yet many of the tracks from a site on the west coast which was some 20 miles north-east from their home, converged and ran together along the coastal highway.
This involved a western deviation from their direct path to their loft. Were they following the road? Many pigeons flew from long distances in parallel with the coastal highway which implies that they were relying on visual cues. One bird flew for six miles on this course despite it being windy close to the sea.
Then when they got within about six miles from the loft, the road-following pigeons appeared to make a directional decision. Typically, they began to circle above the region where the highway separated into two.
Some pigeons, a minority, then took a direct route to the loft flying over creeks and valleys. The other pigeons turned sharply towards the road that left the highway and led to their loft, although it added four miles to the flight.
These observations suggest that pigeons can find their loft using a compass mechanism, but many prefer to use a road-following strategy, which may involve the construction of a mental map. Large roads can stabilise flight direction when they are far from home. This causes the pigeons to add extra mileage to their journey home, though this turned out to be small. But the flight paths along the roads were at a lower altitude and they flew at a slower rate. Flights across the countryside or hills were at a higher altitude and faster, and there were more local errors in direction finding. On balance, following the road cost more in energy spent. Perhaps they just prefer to fly along familiar paths rather than unfamiliar countryside guided by their compass. It may also free the pigeon's brain from consciously doing a difficult task, and so allows them to focus on other tasks, such as looking out for predators.
Earlier studies did not provide similar evidence and suggested instead that pigeons were attracted chiefly by topographical features they were familiar with, such as the type of village and type of landscape. So it is important to realise that in these new studies the pigeons had grown up in the region and had already been trained to return to their loft. There is also some preliminary evidence that in long - 190-mile - runs of Belgian racing, pigeons do use road following.
Whatever future research shows, it is clear that pigeons have a remarkable ability to switch from one homing strategy to another. Genes have done amazing things to their brains.
Professor Wolpert is professor of biology as applied to medicine at University College London
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