Caribbean parrots thought to be endemic are actually relicts of millennial-scale extinction

Researchers have isolated the first ancient DNA from Caribbean parrots and matched it with genetic sequences from contemporary birds in a new study that was published in PNAS. Using fossils and artifacts from archaeology, they demonstrated the extensive and diversified resurgence of two species previously believed to be isolated to certain islands.

With 28% of all species thought to be vulnerable, the findings help explain how parrots quickly rose to the top of the list of endangered bird species worldwide. This is particularly true for island-dwelling parrots.

When Christopher Columbus visited the Caribbean for the first time in 1492, he saw that parrot flocks were so large that they "obscured the sun." More than half of the Caribbean's parrot species—from massive particolored macaws to sparrow-sized parrotlets—are now extinct.

The fact that so little is known about the historical ranges of the surviving parrot species poses a challenge to biologists working to protect them. This is mostly because of their complex past with humans.

Lead author Jessica Oswald, a senior biologist with the U.S. Fish and Wildlife Service Forensics Lab, noted that "people have always been obsessed with parrots." For thousands of years, native peoples have transported parrots between islands and continents. That tradition was later carried out by European colonists, and we still move them around today."

Due to centuries of trade and exchange, it is impossible to determine how parrots came to be at their current location. It is uncertain if native parrots originated on the islands they now reside on or were similarly moved there. Of the 24 parrot species that are presently found in the Caribbean, half were brought from other regions.

Luckily, parrots are also occasionally found at archaeological sites due to their fondness with people. Their bones, together with shells, fish bones, and other food remnants from past meals, have been found in waste heaps known as middens.

"Records exist of parrots being kept in homes, where they were prized for their feathers and, in certain situations, possibly as a source of food," said Michelle LeFebvre, the Florida Museum of Natural History's senior curator of South Florida archaeology and anthropology.

When compared to other tropical places, the fossil record for parrots in the Caribbean is quite good. But whole specimens are hardly discovered. The majority of the time, their bones are fragmented or damaged, and it's not always clear to which species they belonged to.

In situations when physical comparisons cannot yield clear answers, co-author David Steadman was keen to investigate whether any remaining genetic material might be extracted from bone tissue.

As a graduate student and postdoctoral associate at the Florida Museum, Oswald had just finished a proof of concept project in which she had successfully sequenced the first DNA from a long-extinct bird from the Caribbean that had been preserved for 2,500 years in a blue hole. Afterwards, using the same techniques, she found that extinct flightless birds from the Caribbean shared the greatest degree of phylogeny with similarly extinct ground-dwelling birds from Africa and New Zealand.

"We can use fossils in ways that weren't even imaginable when they came out of the ground," stated Steadman, a former Florida Museum ornithology curator. "For me, that is the single most satisfying thing about this project."

With the use of old DNA samples from two species of parrots—the Cuban (A. leucocephala) and Hispaniolan (A. ventralis) parrots—the authors put together the lengthy history of parrots in the genus Amazona.

Nowadays, Cuban parrots are the more common of the two; isolated populations may be found throughout Cuba as well as on a few islands in the Bahamas and Turks & Caicos. They are among the few native parrots left in the area that are not in immediate risk of going extinct.

The Hispaniolan parrot has found it more difficult to adjust to changes brought about by humans. It is completely endemic to its named island and is categorized as vulnerable to extinction on the Red List of the International Union for Conservation of Nature.

As a result, the majority of the fragmented fossils found outside of Hispaniola and Puerto Rico were determined to be from the more prevalent Cuban parrot species. However, the results of the DNA test revealed a different picture. Prior to the introduction of humans on the islands, the Hispaniolan parrot was the species that historically inhabited the Bahamas, as evidenced by the fossils found in paleontological sites in the Bahamas.

In a similar vein, the findings suggest that Cuban parrots were formerly resident on the biggest island in Turks and Caicos, from which they have since disappeared.

"The finding of what may be regarded as dark extinctions is one of the remarkable aspects of this study," LeFebvre stated. "We are discovering diversity that, until we looked more closely at museum specimens, we had no idea existed."

It was also established that the bones were from Hispaniolan parrots from archaeological sites in the Turks and Caicos and Montserrat, an island located far to the south in the Lesser Antilles. The species was extinct from the islands when these were brought there, most likely by humans.

According to Oswald, the first step in preserving what remains of a species' variety is to identify the areas where it historically flourished, both naturally and artificially with human assistance.

She remarked, "We have to consider what we think is natural." Since people have been modifying the natural environment for thousands of years, it is possible that certain species that we consider to be unique to a particular region are really products of recent human-caused range loss. To truly comprehend the long-term impact of humans on variety change, paleontologists, archaeologists, evolutionary biologists, and museum scientists must collaborate."

The study's co-authors are Robert Guralnick of the Florida Museum of Natural History, Julie Allen of Virginia Tech, and Brian Smith of the American Museum of Natural History.