About 12% of the world’s bird species have been driven to extinction by human activity, new research has found – double previous estimates.
Known bird extinctions, identified using fossil or other records, account for approximately 640 species. The new estimate includes the birds that went extinct without the event being recorded – what scientists call a dark extinction.
“We know we’ve lost iconic birds like the dodo, but we wanted to get a better estimate of the bird extinctions we didn’t know about,” said Dr Rob Cooke, an ecological modeler at the UK Center for Ecology and Hydrology and the newspaper’s chief writer.
To calculate the number of unknown extinctions, Cooke and his team extrapolated from the 640 bird species known to have gone extinct, using a statistical model. The model used New Zealand as the baseline for bird species loss on the basis that the country had no known extinctions.
“New Zealand has been the benchmark, it has the most complete bird record based on found fossils and bird sightings, so it’s ground zero, there’s nothing that’s not observed in New Zealand.”
Using the New Zealand data, the team made an estimate of how many species might have lived on an island. They then subtracted the number of known extinctions and the remaining living birds. The result is the number of undetected extinctions.
The study focused on island bird populations because non-migratory birds cannot disperse easily. “Islands are the best place to study extinctions: 90% of extinctions are on islands because island birds have nowhere else to go,” Cooke said.
Deforestation, overhunting, fires and invasive species are key causes of the loss of bird species, Cooke said.
The team’s new bird species extinction total of 1,430 may be on the low side, Cooke said. “The losses could be even higher, maybe up to 2,000, but we wanted to be conservative.”
Major extinction events occurred in the 14th century, the paper found, when “the largest human-driven wave of vertebrates so far recorded” caused species loss in the eastern Pacific at nearly 100 times the natural extinction rate. The extinctions were driven by human settlement, which brought deforestation and the introduction of invasive species.
High numbers of bird extinctions, the paper says, are a loss to “our understanding of bird species richness, ecological diversity and evolutionary history”.
“The world is emptier than we realize,” Cooke said. “And these missing birds are a loss to our imagination.”
Also missing are the important roles these birds would have played in the wider environment. Birds play a essential role in the earth’s ecosystems spreading seeds, pollinating plants, cleaning carcasses and helping to fertilize coral reefs and the land with their manure.
Known bird species losses, the paper said, include “extinct megaherbivores such as the elephant birds (Aepyornithidae) of Madagascar, which affected plant structure and diversity and ecosystem dynamics, extinct aerial predators such as Haast’s eagle (Hieraaetus moorei), and extinct seed dispersers such as Seychelles parakeet (Psittacula wardi).”
Dr Alexander Lees, a reader in biodiversity at Manchester Metropolitan University, who was not involved in the research, said: “That the study shows convincingly that we have mismeasured the bird extinction crisis does not surprise me at all. Most birds have very small bones and do not fossilize easily; many islands are not conducive to fossil formation; and in many places no one has yet looked for fossils.”
The estimated bird extinction rate voted recent estimates of mollusc extinctions, he said, and was “a useful way to approach the extinction crisis and understand what we’ve lost”.
Future extinction, Cooke said, will continue if the world continues as normal. Previous research by the same team of scientists suggests that the world is at risk of losing another 669 to 738 bird species over the next few hundred years, with species facing increasing pressure from the climate crisis, reduced food resources and deforestation.
“Recent conservation has saved some species, and we must now increase efforts to protect birds with habitat restoration led by local communities,” he said. The future for bird species “rests with us”, he added.