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About 136,000 years ago, on a coral atoll in the Indian Ocean, there lived a flightless bird. And when this atoll was swallowed up by the waves, that bird went extinct. ... Or did it? Did the flightless Aldabra rail evolve twice?

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Sources:
https://www.nhm.ac.uk/discover/news/2019/may/birds-on-an-island-in-the-indian-ocean-evolved-flightlessness-twice.html
https://www.nature.com/articles/s41598-022-05329-1
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192675#pone.0192675.ref009
https://researchportal.port.ac.uk/files/20131781/Repeated_evolution_of_flightlessness.pdf
https://birdsoftheworld.org/bow/species/whtrai1/cur/introduction
https://royalsocietypublishing.org/doi/10.1098/rstb.1971.0022
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6927662/
http://www.seychellesnewsagency.com/articles/1327/Seychelles+Islands+Foundation+working+to+classify+Aldabra+Rail+as+a+separate+species
https://carnegiemnh.org/a-match-made-by-coevolution/
www.researchgate.net/profile/Andrej-Spiridonov-2/publication/339308200_Moving_towards_a_better_understanding_of_iterative_evolution_an_example_from_the_late_Silurian_Monograptidae_Graptolithina_of_the_Baltic_Basin/links/605bd652299bf17367686519/Moving-towards-a-better-understanding-of-iterative-evolution-an-example-from-the-late-Silurian-Monograptidae-Graptolithina-of-the-Baltic-Basin.pdf
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192675#references
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Thumb Image Credit: Ian Davies / youtube.com/@theBirdsGuy
Images:
https://commons.wikimedia.org/wiki/File:Darwin%27s_finches_by_Gould.jpg
https://commons.wikimedia.org/wiki/File:Dryolimnas_cuvieri_abbotti.jpg
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192675#references
https://search.macaulaylibrary.org/catalog?taxonCode=whtrai1&subId=S120646384
https://search.macaulaylibrary.org/catalog?taxonCode=whtrai1&subId=S54342870
https://www.flickr.com/photos/biodivlibrary/50884719468/in/album-72157718074612568/
https://www.gettyimages.com/detail//1319245938
https://www.gettyimages.com/detail//1873922239
https://www.gettyimages.com/detail/1189180601
https://www.gettyimages.com/detail/1205723154
https://www.gettyimages.com/detail/1210192652
https://www.gettyimages.com/detail/1254845401
https://www.gettyimages.com/detail/1298712957
https://www.gettyimages.com/detail/1386115358
https://www.gettyimages.com/detail/1422137124
https://www.gettyimages.com/detail/1456401923
https://www.gettyimages.com/detail/1457477523
https://www.gettyimages.com/detail/1461341351
https://www.gettyimages.com/detail/1759260858
https://www.gettyimages.com/detail/1932566415
https://www.gettyimages.com/detail/2029974605
https://www.gettyimages.com/detail/472674730
https://www.gettyimages.com/detail/487966660
https://www.gettyimages.com/detail/491293328
https://www.gettyimages.com/detail/666002424
https://www.gettyimages.com/detail/820677950
https://www.gettyimages.com/detail/1311051529
https://www.inaturalist.org/observations/105320184
https://www.inaturalist.org/observations/4425241
https://youtu.be/d0WD7VAPbFg?si=0sEIwVNVcVCJjYe7
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About 136,000 years ago, on a coral atoll  in the Indian Ocean, there lived a bird. Over time, it had lost its ability to fly, like  many island birds do in the absence of predators. But, the thing is, coral atolls  are not the most stable of landscapes.

They tend to be low-lying – often just a few meters above sea level, at most. And when this atoll was swallowed up by the waves,  there was nowhere for that flightless bird to go. It went extinct, along with  all the other unique species   that had only evolved on that single island.

They were gone, forever. Or…were they? [♪♪ INTRO ♪♪] If you want to support the channel,   the Bizarre Beasts pin club will now be  open for subscriptions for the whole month! Sign up by May 20th and the first pin you  will get will be this very good Aldabra rail.

And don’t forget to stick around at the  end of the video for some bonus rail facts. Now, this story might sound familiar,  but just bear with me for a bit. Today, ocean levels have once again receded  and that island is back above sea level.

And the Aldabra rail is a terrestrial bird  that lives on that island, the Aldabra Atoll,   in the Seychelles, a country made  up of islands in the Indian Ocean. It is about 30 cm long and has a  patch of white feathers at its throat. And it’s an omnivore and occasional scavenger,   though it prefers to eat  insects when it can find them.

It also sometimes takes on crabs,   which sounds very reasonable for  a bird that lives on an island… but these are not tiny, adorable little crabs. They are large and the researchers  we talked to for this episode gave   us a bunch of very classic nature  documentary-style rail versus crab footage, which I’m going to take  a second to just, like, appreciate here. Now, there are a couple of things  about the Aldabra rail that are weird.

Like, it’s either a separate, distinct species  of white-throated rail or one of three subspecies   endemic to islands throughout this  region, depending on who you ask. Defining a species can be messy and  subspecies are even harder to define. But the thing that definitely makes it different  from the other living white-throated rails is   that it is the last surviving bird  in the Indian Ocean that cannot fly… and that’s where this story  starts to get even weirder.

The first thing to know is that there are  a lot of different flavors of evolution. For example, you’ve got convergent evolution,  where different species evolve to have similar traits independently of each other, like how a ton of unrelated crustaceans evolve to be crab-shaped. And you’ve got divergent evolution,  where populations of the same species get separated   and accumulate differences over  time, potentially ending up as different species.

Darwin’s finches are the classic example. And then there’s coevolution, where two or  more species influence each other’s evolution,   like certain hummingbirds and the  specific flowers they pollinate. But perhaps the least common of  the flavors is iterative evolution: when species within the same group  repeatedly evolve the same traits   independently at different points in time.

And this can make it look like  species go extinct and then re-evolve. But do they really? Back in 1987, a paleontologist named John Becker   collected a large number of fossils  from a couple of sites on Aldabra… but he didn’t bring back just  the fossil bones, themselves.

He collected them still encased in the hardened  sediment they were buried in. This is pretty  common for paleontologists, especially when they’re dealing with fragile fossils. But it means that, once the  fossils get back to the lab,   you have to get rid of that sediment,  in a process called preparation.

That can sometimes take years… decades, even, if there’s no one with  the time and skills to do the work. But, in the mid 2010s, researchers finally got   the chance to work their way  through those fossil blocks. And they found two intriguing bones: a complete left humerus, or upper arm bone, and  the lower part of a right humerus of a bird.

And they looked almost exactly like the arm bones of the flightless rail that lives on Aldabra today… except they were over 136,000 years old,   which mean they came from the time  before that island was completely flooded. Now, these aren’t the only rail bones  that have ever been found on Aldabra. There’s also a piece of a foot bone from after the   island flooded that also looks like  the foot bone of a flightless rail.

So, according to the researchers, this  means that there were flightless rails   on Aldabra before the atoll flooded around  136,000 years ago. Then they went extinct because the atoll was gone and they couldn't fly. Then another group of white-throated  rails flew to Aldabra after it emerged again… And then they evolved to become  flightless in under 16,000 years,   which is potentially the fastest evolution  of flightlessness in a bird that we know of.

And their descendants still  live on the atoll today. Which sounds a lot like the same  flightless Aldabra rail evolved twice… and that’s what a lot of the press coverage  said when the paper about it came out. Of course that's not really how evolution works.

The old Aldabra rail is extinct, for good. What probably happened both times is  just a weird quirk of how rails behave: when there are enough of them on an island,   like Madagascar where white-throated rails  live today, they sometimes just disperse... They fly off to isolated islands, settle there,   and often become flightless, probably in  part because they nest on the ground anyway.

And Aldabra isn’t the only island that has had  a unique flightless or semi-flightless rail. And maybe this is splitting  scientific hairs a bit,   but just because the two Aldabra rails  descended from the same population and   adapted to island life in the same way  doesn’t mean they’re the same species. Because, for evolution, genetic variation  matters a whole lot.    It’s the raw material natural selection can act on when the  environment around a species changes.

If there’s no variation, it can be hard  for a species to adapt and survive. And, for example, we don’t know  if the extinct rail and the living one    ended up with the same genetic  variants from the parent population. Which means that they could look very similar, but  under the hood, have different variants of genes   that would result in different evolutionary  futures when faced with the same challenges.

So, ultimately, what we can say is  that there have been two iterations   of flightless Aldabra rails, but  they are not the same Aldabra rail… And each was its own Bizarre Beast. Don’t forget to sign up for the pin  club at BizarreBeastsShow.com by May 20th if you want one of these incredible pins. And now for some bonus facts… [♪♪ BONUS FACTS ♪♪] So, now that we’ve introduced  you to the Aldabra rail,   you might be wondering what  other rails are out there.

I though it was just a part of a train track. And you are in luck, because there’s  something like 127 species of them   distributed worldwide, just not at high latitudes. They tend to be slender, secretive marsh birds,   and the ones with short bills are often called  crakes, so you might know them by that name, too.

Or, you might be more familiar with their  cousins, the coots and the gallinules! In the episode, we mentioned  that the Aldabra rail is the   only native flightless bird living  on an island in the Indian Ocean. But there used to be others!

You might’ve heard of the most famous one,   the dodo, which lived on Mauritius until 1681. But the dodo wasn’t the only one. There also used to be more flightless rails,   including one that lived on Réunion until  at least the end of the 1600s and another   that was probably flightless and lived  alongside the dodo on Mauritius until 1638.

Surviving as a flightless, ground-nesting  bird on an island when humans arrive and   bring animals like pigs and rats with them  is challenging and, more often, tragic. Island birds often become flightless to   save energy and devote it to more  important aspects of life instead. When we humans want to optimize our energy  levels though, the best thing we can do   is to optimize our sleep, and that's where  this episode’s sponsor Manta Sleep comes in.

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But I'm not 100% sure, I can't see the teleprompter. Yes 10%! 10%! Mantasleep.com! [♪♪ OUTRO ♪♪]