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The bar-tailed godwit makes the longest nonstop flight of any bird: From Alaska to New Zealand. And they have to shrink their organs to do it.

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Host: Hank Green (He/Him)

Think back to the longest road trip of your life.

Maybe it took 8 hours, maybe it took 24, maybe it took 5 days. You probably took some breaks, if only to grab something to eat, use the bathroom.

Now imagine it again, except you cannot stop and there are no snacks. Also, your body is the car, so you absolutely do not have space for any baggage. Oh, and the road trip is now 9 full days and nights long.

And all your digestive organs literally shrunk to prepare you for this. [♪♪ INTRO ♪♪] That is life for at least one subspecies of shorebird known as the bar-tailed godwit. There are at least four, and maybe even five or six, different subspecies of bar-tailed godwits, depending on which ornithologists you ask. These groups are split up by where they breed, where they migrate, and by slight differences in how they look.

Bar-tailed godwits can be found all across the Arctic in the summer months of the Northern Hemisphere, from Alaska to Siberia to northern Europe. They breed in the dry spots of swamps, bogs, and marshes, as well as wetlands and river valleys, basically, near wet places across the tundra. And they feed on things like crustaceans, annelid worms, bugs, and bivalves, which they find by sticking their long beaks into the mud.

Another thing they all have in common is that they fly south for the winter, and spend their time in habitats like tidal mudflats, estuaries, and coastlines. But how far south they go depends on the subspecies. The European bar-tailed godwit breeds around the White Sea and in northern Scandinavia.

And it only migrates 1500 to 2000 kilometers to the North Sea for winter. Which still counts as a long-distance migration, even though it’s shorter than the distance your average Canada goose flies. But the ‘baueri’ subspecies of bar-tailed godwit goes much, much farther.

One leg of their migration is the longest non-stop flight of any bird. They breed in Alaska, and then fly something like 11,690 kilometers over the Pacific Ocean, to New Zealand, often without stopping. No rest, no food, just 8 to 10 days of continuous flapping.

And if they get blown off course, like one male did in the 2021 migration, and have to make an emergency landing in Australia, that adds even more distance to their trip. Now their return journeys are a little easier, since they stop over in China on the way back to Alaska, but the whole trip is more than 30,000 kilometers, and they do this every year. Now, why they do this incredible annual feat is a relatively easy question to answer.

They hate winter. I’m mostly kidding. The subspecies typically leaves Alaska in September and October, trading the Northern Hemisphere’s fall and winter for the Southern Hemisphere’s spring and summer.

Not having to deal with bad weather is an obvious benefit for the birds. And both their winter and summer homes are rich in food resources, which is important for breeding and raising chicks, and for fueling up for their epic flights. New Zealand’s coasts also lack birds of prey that would hunt shorebirds, so the bar-tailed godwits can fatten back up for their return flight undisturbed.

So that’s why. But how they do this migration, is wild. Like, if we were to do any of this this fast as humans, it would be just incredibly bad for us.

The first thing to know is that powered flight, the part where a bird flaps their wings instead of soaring or gliding, takes a lot of energy, so it’s important for a bird to be lightweight. But the best way to store enough energy to flap for 8 or 9 days straight is to fatten up, which obviously runs counter to trying to stay light. For these bar-tailed godwits, those competing demands mean that they need to cut their body weight down as much as possible before leaving Alaska, which means getting rid of the stuff they don’t need on the trip.

And what they don’t need on the trip are full-size digestive organs, because they don’t eat during their flight. Their livers, kidneys, stomach and intestines literally shrink. Their bodies just absorb up to a quarter of the tissue that makes up these organs and then they regrow them when they get to New Zealand.

While that’s going on, the relative size of their flight muscles increases. They need all that additional muscle power to carry all the extra fat they put on to fuel their flapping. One study found that over half of a godwit’s mass during their migration was fat.

And these radical transformations of their bodies take place in less than a month! And while all of these changes seem to make sense, in terms of their benefits to the godwits on their migration, there’s still a lot of stuff about these birds that we do not understand. Like, we’re not sure whether the godwits can sleep at all during their flight.

Some other animals, like great frigatebirds and dolphins, can sleep with half of their brain at a time while soaring or swimming. And we don’t know for certain how the bar-tailed godwits and other long-distance fliers navigate over huge and relatively featureless parts of the Pacific Ocean. We’ve uncovered some of the secrets of their bodies, it seems, but these aspects of their brains are still a mystery.

And while knowing how they manage to migrate so far might make them seem less strange to us in some ways, in others, they are definitely still bizarre beasts. The Bizarre Beasts pin club subscription window is open from now through the end of November 14th! Sign up today to never miss a beast!

The bar-tailed godwit pin is AMAZING. Be sure to keep an eye out for new merch dropping on November 11! Just a little something exciting for you all.

And, as always, profits from the pin club and all of our merch go to support our community’s efforts to decrease maternal mortality in Sierra Leone. [♪♪ OUTRO ♪♪]