This Carolina parakeet was collected sometime in the late 1800s.
(c) Pilar RodrÃguez 2019. All rights reserved
Not very long ago, wild parrots lived in the forests of New York. The brightly-colored birds squawked among the treetops of old-growth riverine forests and swamps from Florida to New York and as far east as Colorado, gathering in flocks of hundreds at a time. Today, the great vociferous flocks are gone, and the bright green, red, and yellow plumage can be seen only in museums.
The last known Carolina parakeet was born sometime around 1883 and died in the Cincinnati Zoo in 1918, in the same ill-fated cage where the world’s last passenger pigeon had died in 1914. Inca, the last Carolina parakeet, had outlived his mate, Lady Jane, by around a year – and as far as anyone knew, the pair had outlived their wild relatives by nearly a decade. No one had reported a credible sighting of a wild Carolina parakeet since 1910.
The Carolina parakeet has been extinct for roughly a century, and a new genetic study pins the blame squarely on humans.
The Last Stand Of America’s Parrots
As European settlers and their descendants pushed westward in the 1700s and 1800s, they cleared many of the forests the Carolina parakeet had once called home. They also shot the birds in droves to keep them away from grain fields and to collect their bright feathers for ladies’ hats. The Carolina parakeet made an easy target; flocking instinct would bring large numbers of birds back to the scene of a fresh kill, giving hunters another shot at them.
By the mid-1800s, Carolina parakeets were rare outside the swamps of Florida, and by 1900, they couldn’t be found anywhere else. But even in their last bastion of habitat, Carolina parakeets seemed to be doing pretty well, under the circumstances. Farmers had stopped hunting them, because they turned out to be useful for keeping cockleburs in check (the Carolina parakeet was one of the only animals who could survive eating the poisonous plant, although the toxic glucoside accumulated in the birds’ flesh and made them deadly prey. Cats who ate Carolina parakeets usually died soon after). And naturalists described large flocks, with plenty of young birds and good access to nesting sites.
And then, abruptly, the Carolina parakeet simply vanished. A century later, ecologists still don’t understand what happened. Maybe, some say, the species wasn’t faring as well as it looked from the outside; population decline and habitat loss could have left them with a limited gene pool, doomed to fade away before too long. But maybe, others argue, the Carolina parakeet would have been just fine if they hadn’t been exposed, in their last refuge, to deadly poultry diseases like Newcastle Disease from nearby farms.
“If this is true, the very fact that the Carolina parakeet was finally tolerated to roam in the vicinity of human settlements proved its undoing,” wrote the Audobon Society a few years ago. There’s no actual evidence to support the poultry disease hypothesis: no eyewitness report of sick parrots with symptoms of something like Newcastle Disease, and no smoking gun in the form of pathogen samples from a preserved parrot corpse. But a new study, published in the journal Current Biology, sequenced the Carolina parakeet genome for the first time and searched for signs of inbreeding or population decline – and found none. That means the species wasn’t doomed long before its disappearance, which means something must have tipped the balance.
Solving A Cold Case
Evolutionary biologist Carlez Laluzela-Fox and colleagues sampled nuclear DNA from the tibia (shin bone) and toe pads of a Carolina parakeet, killed and stuffed in the late 1800s and now owned by a private collector in Spain. They used the genome of the extinct species’ closest living relative, a South American parrot called the sun parakeet, as a reference to help them map the genome and understand what the sequences of adenine, thymine, guanine, and cytosine meant for the birds’ actual physiology.
“Demographic declines leave specific signals in the genomes of the species,” explained Laluzela-Fox in a statement to the press. If members of a species have spent several generations breeding with close genetic relatives, or if the overall breeding population was too small, geneticists can spot the signs in an organism’s genome.
But the Carolina parakeet genome had none of those warning signs – so its sudden extinction wasn’t the end of a much longer decline. Something new had happened – and the odds are good that it was our fault. That lends some support to the poultry disease idea, although it’s a long way from actually proving that sick chickens, and not some other problem, actually killed off the Carolina parakeets.
Meanwhile, Laluzela-Fox and colleagues say that the same process they used to look for signs of population decline in the Carolina parakeet genome could also help screen living species for warning signs – and maybe solve more extinction cold cases, too.
The genomic study also solved another century-old mystery: how did the Carolina parakeet live on poisonous cockleburs, when their toxins even made the bird’s flesh too poisonous to eat? In the Carolina parakeet’s genome, Laluzela-Fox and colleagues found two proteins that interact with the toxic glucoside in cockleburs. They suggest that those proteins allowed the bird to safely enjoy its toxic treats.