Caribbean parrots are relics of human-driven millennial-scale extinction, research shows
Parrots thought to be endemic were moved from elsewhere
On his first voyage to the Caribbean in 1492, Christopher Columbus noted that flocks of parrots were so abundant they “obscured the sun.” Today, more than half of parrot species in the Caribbean have gone extinct.
In a new study published in PNAS, researchers have extracted the first ancient DNA from Caribbean parrots, which they compare with genetic sequences from modern birds. The results help explain how parrots rapidly became the world’s most endangered group of birds, with 28 percent of all species considered to be threatened. This is especially true for parrots that inhabit islands.
Parrots and people traveled together
Biologists attempting to conserve the remaining parrot species are stymied by how little is known about where they originally lived. This is due, primarily, to their complicated history with humans.
Julie Allen is an assistant professor in the biological sciences department in the College of Science at Virginia Tech and the lead principal investigator on a National Science Foundation grant.
“Understanding the full extent of humans’ impact on species distributions requires combining ancient DNA with archeological and museum data. This study was an exciting example of this process. We were able to tease out the impacts that ancient humans had on past parrot distributions, helping us to understand the current distributions of the remaining species.”
Movement of parrots was impacted by:
- Centuries of trade
- Half of the 24 parrot species in the Caribbean now were imported from other areas
- Even parrots thought to be native have been transported between islands by humans
Human’s historical fondness of parrots is helping to solve the puzzle
Fortunately, parrots’ popularity with humans means the birds are occasionally found in archaeological sites. Their bones have been recovered from refuse piles — called middens — alongside shells, fish bones, and other scraps from previous meals.
“There are records of parrots being kept in homes, where they were valued for their feathers and, in some cases, potentially as a source of food,” said senior author Michelle LeFebvre, curator of South Florida Archaeology and Ethnography at the Florida Museum of Natural History.
Modern DNA science to the rescue
Parrots also have an uncharacteristically good fossil record in the Caribbean, but their specimens are rarely ever found intact, making identifications difficult.
DNA can provide unequivocal answers where physical comparisons fall short, and co-author David Steadman, retired curator of ornithology at the Florida Museum of Natural History, was eager to see if they could extract any residual genetic material preserved in bone tissue.
“For me, the single most satisfying thing about this project is we can use fossils in ways that weren’t even imaginable when they came out of the ground,” said Steadman.
The authors pieced together the long history of Amazona parrots through DNA by:
- Focusing on two parrot species — the Cuban (A. leucocephala) and Hispaniolan (A. ventralis)
- Collecting ancient fossil fragments outside of Hispaniola and Puerto Rico and using DNA methods to identify them
Of the two, Cuban parrots are currently the most widespread, with isolated populations in Cuba and a few islands in the Bahamas and Turks and Caicos. They have a comparatively rich fossil record across numerous islands, making them an excellent focus for understanding historical and modern diversity patterns.
The Hispaniolan Parrot has had a harder time adapting to human-wrought changes. It’s listed as vulnerable to extinction and is entirely endemic to its eponymous island.
Most of the fragmentary fossils collected outside of Hispaniola and Puerto Rico were previously believed to belong to the more common Cuban parrots. But when the DNA results for the ancient fragments came back, they told a different story:
- The fossils from the Bahamian paleontological sites were actually from Hispaniolan parrots, indicating that this species formerly had a range that extended up through the Bahamas prior to human arrival to the islands.
- Similarly, the results indicated that Cuban parrots once inhabited the largest island in the Turks and Caicos, from which they are now absent.
According to lead author Jessica Oswald, a senior biologist with the U.S. Fish and Wildlife Service Forensics Lab, knowing where species once thrived, both naturally and artificially with the aid of humans, is the first step to conserving what’s left of the species' diversity.
“We have to think about what we consider to be natural,” she said. “People have been altering the natural world for thousands of years, and species that we think are endemic to certain areas might be the product of recent range loss due to humans.”
Jerald Pinson of the Florida Museum of Natural History contributed to this article