In October 2022, an astonishing piece of wildlife news captured the attention of scientists around the world. A young bar-tailed godwit, identified only as B6, completed the longest non-stop journey ever recorded for any animal, from Alaska to Tasmania in one unbroken journey. How does a young bird cross an ocean, alone, to get to a specific place it has never before been?
On most dives, the day’s adventure begins long before the descent into the sea. As the dive boat heads offshore, seabirds appear almost immediately. Gulls wheel overhead, shearwaters skim effortlessly across the waves, terns plunge after fish, while farther offshore an albatross may be gliding for minutes at a time without a single wingbeat.
Seabirds live on the air and sea. They drink seawater, sleep on the waves, dive for their food, and may spend months—or even years—without returning to land. Their lives are so perfectly adapted to wind and water that most species cannot support their own weight on land and spend time there only while nesting.
But the godwit’s relationship with the ocean is entirely different. It is a wading shorebird, adapted for probing tidal mudflats with its long bill and striding through shallow water on its long legs. To a godwit going to its southern habitat, the ocean is an obstacle. Its feathers are not waterproof, so it cannot alight on the water to rest. Night and day, it must keep flying on towards land.
Seabird feathers are a miracle of evolution
The feathers of seabirds have a complex and precise structure. From each side of the shaft of each feather branch hundreds of filaments called barbs. And hundreds of tiny filaments, called barbules, branch from each barb. Upon each barbule is a row of microscopic hooks called hooklets. The hooklets interlock with the barbules on the next barb, which causes the feathers to mesh together like Velcro. Taking advantage of the strong surface tension of water, the microscopic meshing of hooklets and barbules creates a waterproof sheath that keeps the bird dry.
That is why seabirds are so often seen preening their feathers. To maintain their waterproofing, each day, they carefully preen each one.
Any oily film in the water destroys the feathers’ delicate structure so that the hooklets and the barbules cannot lock together. The bird loses its waterproofing and is soon wet and cold. That is why oil spills are lethal for all aquatic birds, including ducks and geese. It only takes a drop of oil the size of a quarter to kill a bird.
Many seabirds possess other remarkable adaptations. Tubenoses such as albatrosses and petrels have glands above their eyes that remove excess salt from the seawater they drink, allowing them to live where fresh water is unavailable. Long, narrow wings enable them to sail on ocean winds, travelling immense distances with little effort.
But godwits lack these specialised adaptations. Their plumage is perfectly adequate for rain and shallow water, but not for floating on the ocean. If forced down far from land, they would get wet and be unable to get back in the air to resume their flight. Every migration, therefore, becomes an all-or-nothing gamble. Once committed, there is no safe place to stop.
A drastic transformation
Before setting off, the godwit undergoes one of the most extraordinary transformations in the animal kingdom. For weeks it feeds constantly, building enormous reserves of fat until its body weight nearly doubles. This fat becomes the fuel that will power every wingbeat across the Pacific Ocean.
At the same time, organs that will not be needed during the flight begin to shrink. The stomach and intestines become much smaller. The bird will not be eating during migration. Even parts of the liver and kidneys are reduced in size. The bird literally redesigns its own body into the most efficient flying machine possible, carrying only the tissues it needs for the journey ahead.
It even carries its own supply of water. As fat is broken down to release energy, the process also produces water, allowing the bird to remain hydrated despite flying for so many days without a drink.
Yet physiology is only part of the mystery. The route from Alaska to Tasmania crosses thousands of kilometres of open ocean. There are no roads, no mountain ranges, and almost no islands where a tired bird could recover. Unlike birds flying over continents, there are no landmarks to guide it on its journey.
How do they know the way?
Scientists believe godwits combine several sources of information. They probably use the position of the sun by day, the stars by night, Earth’s magnetic field, the direction of prevailing winds, and an internal biological clock that helps integrate all these signals. Exactly how the brain combines this information into a reliable navigation system, however, remains one of the great unsolved puzzles of animal behaviour.
The mystery deepens when we consider B6 itself.
This was not an experienced adult retracing a familiar route. It was a juvenile making its first migration alone. Somehow, its brain contained enough inherited information to guide it across an ocean to a destination it had never visited. There were no parents leading the way, no landmarks stretching across the Pacific, and no opportunity to practise the route beforehand.
How evolution has encoded such astonishing navigational abilities into the nervous system of a young bird remains one of biology’s most fascinating questions. A human would require years of training to learn to navigate such a route.
Another mystery concerns sleep. Eleven days is an extraordinarily long time to remain continuously active. Some birds have been shown to let one half of the brain sleep while the other remains awake, allowing them to continue flying while still obtaining some rest. Whether bar-tailed godwits rely on this remarkable ability throughout their marathon migrations is not yet known. It is one of many questions that scientists continue to investigate.
Modern satellite transmitters now allow researchers to follow birds like B6 across entire oceans in extraordinary detail. We know where they fly, how fast they travel, and even how they take advantage of favourable winds. Yet despite all this technology, the deepest mystery remains.
Every autumn, thousands of bar-tailed godwits rise from the mudflats of Alaska and head out over the Pacific. They disappear beyond the horizon carrying enough fuel for an eleven-day flight, trusting instincts that evolved over hundreds of millions of years.
The Pacific stretches beneath the godwit like an endless blue desert. Storms sweep across it. Winds shift. Waves rise and fall thousands of metres below. There is nowhere to land, nowhere to feed, nowhere to drink. Yet somewhere ahead lies a coastline the young bird has never seen.
It follows invisible highways written not on maps, but in sunlight, starlight, magnetic fields, winds and instincts inherited across countless generations. The birds cross one of Earth’s greatest oceans with astonishing precision, arriving at a coastline they have never seen before.
We can now watch every kilometre of its journey by satellite. But we still cannot explain how a bird on its very first migration knows where to go. Sometimes we clearly see that animals know and do things that are far beyond our expectations, as well as our own abilities. Not through magic, but through millions of years of evolution producing solutions that we are only beginning to understand.
Ethologist Ila France Porcher, author of Yes, Fish Feel Pain, The True Nature of Sharks and six other books on wildlife behaviour, spent 15 years closely observing wild fish and sharks in Tahiti, resulting in several scientific papers. Her writings are based on decades of first-hand observations of wildlife and focus on individuality and intelligence, challenging traditional views of animal minds. Her work has been featured on Shark Week, in scientific discussions, conservation debates and international media for its unique blend of field observation, art and science.
