Birds are among the best-studied animal groups, but their prehistoric diversity is poorly known due to low fossilization potential. Hence, while many human-driven bird extinctions — extinctions caused directly by human activities such as hunting, as well as indirectly through human-associated impacts such as land use change, fire, and the introduction of invasive species — have been recorded, the true number is likely much larger. By combining recorded extinctions with model estimates based on the completeness of the fossil record, scientists from the UK Centre for Ecology & Hydrology and elsewhere suggest that at least 1,300-1,500 bird species (around 12% of the total) have gone extinct since the Late Pleistocene epoch, with 55% of these extinctions undiscovered.
Human colonization and associated bird extinctions: human expansion across the planet is classified into four major waves; major human dispersal routes are indicated with arrows, and silhouettes show example fossil (pre-Holocene – 1500 CE) and observed (1500 CE – present) bird extinctions. Image credit: Cooke et al., doi: 10.1038/s41467-023-43445-2.
There are many potential causes of bird extinction connected to human activity today, including habitat loss, over exploitation, and the introduction of invasive species.
Previous analyses of bird extinction rates have focused on well-documented observed extinctions, beginning just over 500 years ago.
However, this approach may underestimate the magnitude of biodiversity loss associated with human activity, as some species of birds may have gone extinct before they were first formally recorded.
To estimate undiscovered extinctions, Dr. Rob Cooke from the UK Centre for Ecology & Hydrology and his colleagues first modeled fossil bird extinctions across 69 archipelagos (1,488 islands) as explained by multiple environmental predictors and the completeness of the fossil record.
They combined these estimates of undiscovered extinctions (archipelagos only) with estimates of fossil and observed extinctions across the globe.
Subsequently, they estimated the extinction date for all bird species lost since the Late Pleistocene and inferred extinction rates of birds through time
“Our study demonstrates there has been a far higher human impact on avian diversity than previously recognized,” Dr. Cooke said.
“Humans have rapidly devastated bird populations via habitat loss, overexploitation and the introduction of rats, pigs and dogs that raided nests of birds and competed with them for food.”
“We show that many species became extinct before written records and left no trace, lost from history.”
“These historic extinctions have major implications for the current biodiversity crisis,” added Dr. Søren Faurby, a researcher at the University of Gothenburg.
“The world may not only have lost many fascinating birds but also their varied ecological roles, which are likely to have included key functions such as seed dispersal and pollination.”
“This will have had cascading harmful effects on ecosystems so, in addition to bird extinctions, we will have lost a lot of plants and animals that depended on these species for survival.”
The dodo (Raphus cucullatus) by Frederick William Frohawk, 1905.
The team’s results show 640 bird species have been driven extinct since the Late Pleistocene epoch — 90% of these on islands inhabited by people.
These range from the iconic dodo of Mauritius to the great auk of the North Atlantic to the lesser-known Saint Helena giant hoopoe.
But the researchers estimated there have been further 790 unknown extinctions, meaning a total of 1,430 lost species — leaving just under 11,000 today.
They also uncovered the largest human-driven vertebrate extinction event in history, during the 14th century, estimating that 570 bird species were lost after people first arrived in the Eastern Pacific, including Hawaii and the Cook Islands — nearly 100 times the natural extinction rate.
They believe there was also a major extinction event in the 9th century BCE, primarily driven by the arrival of people to the Western Pacific, including Fiji and the Mariana Islands, as well as the Canary Islands, and highlight the ongoing extinction event, which started in the mid-18th century.
Since then, in addition to an increase in deforestation and spread of invasive species, birds have faced the additional human-driven threats of climate change, intensive agriculture and pollution.
“Humans have already driven more than one in nine bird species to extinction, with likely severe, and potentially irreversible, ecological and evolutionary consequences,” the authors concluded.
Their paper was published in the journal Nature Communications.
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R. Cooke et al. 2023. Undiscovered bird extinctions obscure the true magnitude of human-driven extinction waves. Nat Commun 14, 8116; doi: 10.1038/s41467-023-43445-2
