Nearly half of bird species are experiencing population decline

It would not be the first time that humans have witnessed the end of a bird species. At least 187 bird extinctions have been confirmed or suspected since the year 1500.

Photo: Mauricio Alvarado Lozada

Birds play a key role for the ecosystem and for man. They are not only pollinators, seed dispersers and ecosystem engineers that facilitate the maintenance of biodiversity, they also support human efforts such as sustainable agriculture with pest control. They have symbolic and artistic values ​​and their observation is a worldwide pastime practiced by millions of people in the world. Because of its importance, it is of concern that 48% of existing bird species worldwide are experiencing population declines.

This is stated by a group of researchers in a study published in the Annual Review of Environment and Resources. In contrast, 39% of species have a stable behavior and only 6% are showing increasing population trends (for 7% of species the behavior is unknown). “We are now witnessing the first signs of a new wave of extinctions of continentally distributed bird species,” said Alexander Lees, lead author, quoted by the science portal, Phys.org. Although the decline is global, there are particular trends.

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In North America and Europe, where bird population research is more regular than in the rest of the planet, the data was more worrying. In North America, scientists reported that 57% of species exhibited decreasing trends (303 of 529 species). Since 1970, nearly 3 billion individual birds have been lost there. In the European Union, the situation is similar: 378 species indicate an overall decrease of between 17% and 19% between 1980 and 2017. In both regions of the planet, the most serious reduction was suffered by migratory birds.

At a global level, tropical latitudes concentrated the majority of threatened birds, precisely the area that has the greatest wealth in terms of species diversity. The tropical Andes, southeastern Brazil, the eastern Himalayas, eastern Madagascar and the islands of Southeast Asia were the places with the greatest problems. One example of this is that although every country and territory in the world is home to at least one globally threatened bird species, ten have more than 75, with Brazil and Indonesia topping the list with 171 and 175 species, respectively.

With this reality, the researchers estimate a general effective extinction rate, that is, the average probability of extinction per species per year, six times higher than the total extinction rate since the year 1500. It would not be the first time that humans have witnessed the end of a species of bird. At least 187 bird extinctions have been confirmed or suspected since 1500, 90% of which are endemic island species concentrated in the Hawaiian Archipelago, mainland Australia and islands, the Mascarene Islands, New Zealand, and French Polynesia.

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Over the past 600 years, the rate of extinctions increased, peaking in the late 19th century, falling slightly in the early and mid-20th century, before rising again in the late 20th century. What could be causing this? “Continuous growth in human populations and especially per capita consumption rates lead directly to the conversion and degradation of primary natural habitats and consequent loss of biodiversity,” the study reads. Although global tree cover increased between 1982 and 2016, this has been driven by afforestation with plantations (often of non-native species).

“Land cover changes caused by human activities have been occurring for millennia and have likely reduced total bird abundance by a fifth to a quarter since pre-agricultural times,” the researchers say. Despite the dark outlook, there is an opportunity to do something. “The fate of bird populations depends to a large extent on halting habitat loss and degradation,” Lees told Phys.org. “That is often driven by the demand for resources. We need to better consider how commodity flows may contribute to biodiversity loss and try to reduce the human footprint on the natural world.”

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