Thanks to Brilliant for supporting this episode of SciShow.  Go to brilliant.org/scishow to learn more.

(Intro)

When you picture a parrot, you might imagine it in a tropical forest, in the Amazon, or an island in the Pacific.  You probably don't picture Denver, but up until only a century ago, the United States was home to its very own species of parrot, the Carolina parakeet.  Parrots are, generally speaking, birds of the order Psittaciformes.  This includes macaws, parakeets, cockatoos, and others.  These birds aren't really native to much of the United States.  One or two central American species make it just north of the Mexican border and a bunch of others have been introduced as released pets, but the Carolina parakeet, Conuropsis carolinensis, was endemic to the US, meaning it lived nowhere else. 

They were small colorful birds around 100 grams in weight with green bodies, yellow heads, and orange faces.  They were most commonly found in the trees along rivers and swamps gathering by the hundreds in infamously noisy flocks.  According to historical reports, they could be found as far North as New York, south to Florida, and west to Colorado.  It was around the mid-1800s that the birds went into a sharp decline and not long into the 20th century, they became entirely extinct in the wild.  

The last captive Carolina parakeet died in the Cincinnati Zoo in 1918, in the very same cage that the last captive passenger pigeon had died just four years prior, but even those these birds are gone, we can still learn a lot about them from what we have left.  At least 720 skins and 16 skeletons of Carolina parakeets are still preserved in museum collections around the world.  Those specimens not only help us understand the birds' anatomy, they can also preserve the birds' DNA.  Seriously, you'd be surprised how long that stuff can last.

In a study published in 2019, researchers sequenced the genome of one such Carolina parakeet specimen, unlocking clues to some lingering questions about how the birds lived and died.  For example, the birds were famous for eating a plant called cocklebur, which is fun because cockleburs are very toxic.  In fact, the birds ate so much of it that according to historical reports, it made them poisonous.  Cats were even reported to have died from eating birds that ate the plant.  

In the new DNA analysis, the researchers noticed unusual mutations in two genes: the genes code for proteins that carry energy between the mitochondria and other parts of the cell.  What's interesting is that these two proteins are specifically disrupted by cocklebur toxin, interfering with the cell's ability to function.  Exactly what those mutations do isn't clear yet, but it could be some sort of genetic resistance to the plant's poisons, a small change that allowed these parakeets to thrive on a specialized diet.  

Unfortunately, a diet of literal poison was nothing compared to the effects of living alongside humans.  We don't know exactly why the Carolina parakeet went extinct, but most researchers agree that humans are at fault, between hunting the birds and destroying their habitat, but while we're pretty confident they're gone, we don't know if their decline was slow in response to various pressures or if they went out like a light.

See, if a species slowly dwindles over time, we would expect their DNA to show evidence of inbreeding and low genetic diversity as their populations gradually shrink.  This new study was on the lookout for large chunks of the genome where each chromosome in a pair had identical gene variants.  This would suggest the birds' recent ancestors were so closely related that they shared a bunch of the same DNA.  These effects can cause a species to go into a spiral towards extinction as their gene pool dwindles, but the new research found no evidence of this.

The Carolina parakeets' extinction doesn't appear to have been slow.  Instead, as the authors of the new study put it, the extinction happened so quickly that it left no traces in their genomes.  This is pretty good evidence that human activity in the 1800s was the leading cause of their disappearance, not some vulnerability inherent to the parakeets.  Parrots are in a bad way.  More than half of all living species are in decline and almost a third are considered globally threatened with extinction.  Based on this research, it seems the Carolina parakeet was so devastated by human activity that its genetic code left little evidence of decline.  By studying other extinct species with different patterns of extinction, we can be better equipped to detect human impacts on modern species and to spot the warning signs before it's too late.

The United States may never have another endemic parrot and that's on us, but the least we can do is learn from this tragedy and preserve the noisy colorful birds still with us.  

The people who solved this parrot's genome had to know both biology and how to make a computer do biology for them.  The better we get at sequencing DNA, the more data there is to handle.  Enter the field of computational biology.  Brilliant.org offers a whole course in computational biology where you can learn how to process the vast amounts of information 21st century methods have created.  These are great skills to have if you want to enter the field or just understand where data like what we talked about today comes from.  All of Brilliant's courses are designed to help you hone your math and science skills and you can find a wide selection covering things like stats and computer science.  They're all interactive and hands-on, too.  The first 200 people to sign up at brilliant.org/scishow will get 20% off an annual premium subscription, so check it out and see if it's right for you.  

(Endscreen/Credits)