The bar-tailed godwit can fly 11,000 kilometers. Nonstop.

As reported at Science Daily in 2010:

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.

And this from a subsequent report:

The last leg of E7's journey is the most extraordinary, entailing a non-stop flight of more than eight days and a distance of 7,200 miles, the equivalent of making a roundtrip flight between New York and San Francisco, and then flying back again to San Francisco without ever touching down.

Since they are land birds, godwits like E7 can't stop to eat or drink while flying over open-ocean. The constant flight speeds at which E7 was tracked by satellite indicate that she did not stop on land.