The Hawaiian crow, or ʻalalā (Corvus hawaiiensis), has been pushed to the brink of extinction by waves of human migration through the Pacific. It exists only in captive breeding programmes in 2023.Credit: ZSSD/Minden Pictures via Alamy
Around one in nine bird species has gone extinct in the past 126,000 years, according to a study published today1 in Nature Communications, and humans probably drove most of those extinctions. The findings suggest the rate of bird extinctions is more than double the number estimated previously — and that more than half of the extinct bird species were never documented.
The global magnitude of these previously undetected extinctions is likely to “come as a shock to many”, says Jamie Wood, a terrestrial ecologist at the University of Adelaide in Australia. “The sobering thing is that this estimate could actually be conservative,” he says.
Over centuries, humans have triggered waves of extinctions among birds and other animals through land clearing, hunting and introducing non-native species. Islands have been particularly badly affected: 90% of known bird extinctions have occurred in these isolated ecosystems. But because birds have lightweight, hollow bones, their remains tend not to be preserved well as fossils. As a result, most analyses of bird extinctions have relied instead on written observational evidence. These records began only around 500 years ago, which makes it difficult to build a picture of species losses over longer periods.
Rob Cooke, an ecological modeller at the UK Centre for Ecology & Hydrology in Wallingford, and his colleagues built a model of bird extinctions by combining documented extinctions, fossil records and estimates of undiscovered extinctions across 1,488 islands. The team factored in a number of predictors for species richness — including island size, climate and geographical isolation — when estimating undiscovered extinctions.
The model suggested that around 1,300–1,500 bird species — about 12% of the total worldwide — have become extinct since the Late Pleistocene (which was an epoch roughly 126,000–12,000 years ago). Human activities are likely to have caused the vast majority of these extinctions. The researchers also estimated that 55% of these vanished species would not have been discovered by humans or left any trace in the fossil record. The sheer scale of the global loss of birds came as a surprise, says Cooke. “Humans have had a much wider impact on bird diversity than previously thought,” he says.
Pacific hardest hit
The authors found that almost two-thirds of all bird extinctions occurred in the Pacific region. Three major extinction waves have occurred since the Late Pleistocene, and the most intense of these waves occurred just over 700 years ago, when people first arrived on islands in the eastern Pacific — particularly Hawaii, the Marquesas Islands and New Zealand. At this time, extinction rates were 80 times higher than would have been expected if humans had not arrived. Cooke says that the introduction of rodents and domestic animals probably led to the loss of species that were well documented during this period, such as the high-billed crow (Corvus impluviatus), which once inhabited Hawaii.
Developing an understanding of how many species have been lost over time could help policymakers to set biodiversity targets, says Folmer Bokma, an evolutionary biologist at Karlstad University in Sweden.
Cooke says that the findings offer important lessons for tracking and conserving the bird species that remain on the planet today. “Whether or not further bird species will go extinct is up to us,” he adds.
Source: Ecology - nature.com
