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Reviving the cold case of the Carolina parakeet extinction
Although the Carolina parakeet was at the brink of extinction in the mid-nineteenth century, the remaining, seemingly healthy population vanished suddenly without a trace. Scientists are now trying to solve this century-old mystery.
During the winter of 1780, a rural town called Schoharie in upstate New York experienced what was perhaps a freak occurrence. A whirlwind of raucous green-and-red birds landed on a house, covering it from roof to ground, then departed as quickly as they came.
The townspeople, who were deeply religious German Palatines, were left shocked and fearful - they believed the apocalypse was upon them.
While that wasn't the case, the sudden and extraordinary event did foreshadow the death of an entire species: North America's only endemic parrot, the Carolina parakeet.
Dr Alex Bond, Senior Curator in Charge of Birds at the Museum, has teamed up with Dr Kevin Burgio, Director of the Conservation Society at the New York City Audubon Society, and others to understand the final process in the peculiar extinction of the Carolina parakeet. The paper is available on bioRxiv.
No one really knows how or why the last Carolina parakeet population died out so suddenly. Speculations included inbreeding leading to a lack of genetic variation, invasive honeybees competing for space, and poultry disease - however, new research shows these weren't the final cause. © Cephas/wiki (CC BY-SA 3.0).
The bloody murder of the Carolina parakeet
The Carolina parakeet was a brilliantly coloured, medium-sized parrot that travelled in large, noisy flocks of around 300. It typically lived in old, swampy forests and was once widespread across eastern North America, from the Gulf of Mexico all the way to southern Ontario.
Alex says, 'You wouldn't think of parrots in North America as they are usually found in the Southern Hemisphere, but they were there. Carolina parakeets were the only endemic parrots of North America, and they were quite abundant all over the eastern and central USA.'
As Europeans settlers arrived and colonised the continent from the east, they started clearing away a lot of forests where the parrots resided, mainly for agriculture and residential life.
The Carolina parakeet was a highly adaptable bird and easily adjusted to this urban encroachment. But their habit of living in large, noisy clusters irritated humans, leading to people shooting them for sport. The bird's diverse diet, which included cultivated seeds, fruits, flowers, nuts and corns, also angered farmers who killed them to protect their crops.
These social birds had a close bond with each other and when one died, the rest of the flock would shriek and gather around it. This made them an easy target and hundreds were killed in one go.
Brooch made from Carolina parakeet feathers displayed on a Victorian walking dress. Part of the Fashion & Feather 2019 exhibition at Cornell University, USA. Photo by Grace Anderson, courtesy of the Cornell Fashion and Textile Collection and Cornell University Museum of Vertebrates.
The nineteenth-century saw the 'plume bloom', a worldwide trend of using feathers in fashion. Middle-class women could be seen with poignantly beautiful feathers - sometimes even whole bodies - mounted on their garments and accessories.
Thousands of parakeets were slaughtered, resulting in the bloody persecution of North America's only endemic parrot. By the early twentieth century, the Carolina parakeet was a rare species, its remaining population largely confined to Florida.
At this point, farmers also realised that parakeets could be useful as they ate cockleburs, an invasive poisonous plant that could do serious damage to the liver if eaten. They allowed parakeets to roam freely, but it was too little too late. The Carolina parakeet was declared extinct in 1939.
However, the story doesn't end there. While habitat destruction and persecution no doubt led to the extinction of these larger-than-life tropical birds, the remaining population had vanished suddenly without a trace.
This was unusual as a dying species would usually dwindle over time, but records show the last population in Florida seemed healthy - there was a sufficient number of juveniles and many nests were left intact.
To this day, nobody knows what happened to the last Carolina parakeet population.
The endangered sun parakeet is the closest living relative to the Carolina parakeet. Research shows the two species diverged about three million years ago, coinciding with the formation of the Isthmus of Panama (the narrow strip of land that connect North and South America).
New facts about the Carolina parakeet unearthed
Using historical accounts and museum collections from around the world, including more than 700 records from the sixteenth century to almost-present day, Alex and the team created a comprehensive database of every known occurrence of the iconic birds.
Alex says, 'We can take someone's description of a trip they went on in 1850 and use that contextual information in an analysis, which can tell us something new about a species that hasn't been around for a hundred years. That's pretty spectacular.'
Historically, the Carolina parakeet was treated as one whole species, or as separate populations. The researchers approached them as two subspecies, which allowed them to research on a refined level.
The scientists discovered the two subspecies went extinct at different times, with the midwestern population dying out around 1914 and the eastern population persisting until around 1940.
'The extinction period between the two subspecies differs by about 30 years, which is a period of quite a lot of change,' says Alex.
'This gives credence to some of the more uncertain sightings in our database, especially from places like Florida and South Carolina from early- to mid-twentieth century. It also shows the two subspecies probably faced different pressures.'
They also learned that the Carolina parakeet's range was around 10 times smaller than previously believed. The two subspecies lived in different climatic territories separated by the Appalachian Mountains.
The eastern subspecies lived in Florida, expanding north along the coast to New York, and southwest to Texas. The midwestern subspecies, on the other hand, covered a lot more ground and could be found from Nebraska to Ohio, down to Louisiana and Texas. There was very little overlap.
A map showing the distribution range of the two Carolina parakeet subspecies
The midwestern subspecies was most likely migrant, moving between breeding and wintering grounds. It also lived in tree cavities year-round, had fully feathered ceres (a soft, fleshy patch near the beak) and probably became inert during the night, all of which allowed it to survive the chilly weather up north.
This mix of characteristics is also found in living parrot species known for surviving colder climates, including the monk parakeet, which has now invaded some of the former ranges of the Carolina parakeet.
How researching extinct species can help extant ones
Poorly researched species have led to misinterpretations in the past, such as the belief that the extinction of the dodo caused the decline in calvaria trees.
Alex's team's new research provides a reliable starting point for future investigations on what drove such an iconic bird into extinction.
'Our research could be used to help protect parrots - a group that is highly threatened - more broadly,' adds Alex. 'What we can learn from past extinction might help us avoid ones in present or future.'
The study highlights that the loss of a species does not necessarily mean the loss of information. While the extinction process of the Carolina parakeet, once full of life and colour, is still unknown, we are one step closer to understanding it and solving this cold case.
