How is it possible to fly 11,000 kilometers without a single break? The record holder for long distance flight outdoes all human-made aircraft. The bar-tailed godwit has very low energy consumption, but this is not enough to explain its success.

Every autumn the bar-tailed godwit undertakes an eight-day journey from Alaska to New Zealand. The bird flies non-stop, without once breaking the journey to rest or eat. Then when spring comes, the bar-tailed godwit makes the 11,000-kilometre journey back to Alaska.

Professor of Ecology Anders Hedenström from Lund University has pondered over how this species of bird can fly so far without stopping. The distance is twice as far as previously known non-stop distances for migratory birds.

Professor Hedenström emphasises that the bar-tailed godwit is far superior to all aircraft constructed by humans when it comes to the art of flying for a long time without a break. The long-distance flight record for aircraft is held by QiniteQ's Zephyr, an unmanned solar-powered craft. It can remain in the air for 82 hours, around three and a half days, compared with the bar-tailed godwit's eight-day flight.

But what is it that makes the bar-tailed godwit able to fly 11 000 kilometres without a single break? How can these birds manage without sleep or food for eight whole days? One explanation is that they consume unusually little energy compared with other species of bird. Anders Hedenström has calculated that the bar-tailed godwit consumes 0.41 per cent of its body weight each hour during its long flight.

"This figure is extremely low compared with other migratory birds," he says.

However, other factors also play a role. It is important to have the right ratio of body weight to size to be able to carry sufficient energy for the entire flight. The energy mainly comprises body fat, and to some extent also protein. It is also important to have an aerodynamic body shape so that air resistance is minimised. A further success factor is flight speed. The bar-tailed godwit is a quick flyer, which means that it can cover long distances in a reasonable time.

A comparison can be made with a completely different group of long-distance travellers from the animal kingdom -- eels. These animals swim a distance of 5 500 kilometres between Europe and the Sargasso Sea, and manage to do it with significantly lower energy consumption than the bar-tailed godwit. However, they maintain such a low speed that they could never travel across the globe as often as the bar-tailed godwit does. To complete the bar-tailed godwit's 11 000-kilometre journey would take the eel 345 days, according to Anders Hedenström.

There are still pieces of the jigsaw missing that could explain the bar-tailed godwit's record non-stop flight. Could the bird's success be due to a particularly good ability to navigate with the help of an inner compass that makes use of the earth's magnetic field, for example? Anders Hedenström notes that there are a number of exciting questions surrounding the bar-tailed godwit's ability not to get lost up in the air.