Study warns half of bird extinctions may be unstoppable

(CN) — In the generations when European colonists were initially settling North America, the passenger pigeon was the most abundant bird on the continent. Observing them in Kentucky in the early 19th century, ornithologist John James Audubon described a flock so large that it darkened the noon sun “as by an eclipse” and so numerous that it took three days to pass overhead.

Billions of passenger pigeons once filled North America, but industrialization, habitat loss and hunting drove them to extinction, with the last known bird dying in 1914 at the Cincinnati Zoo.

Since 1500, about 150 bird species have gone extinct, according to the International Union for the Conservation of Nature. A study published Tuesday by the University of Reading warns that extinction risks are accelerating, with more than 500 bird species now at risk in the next century, half of which may already be beyond saving.

“Many birds are already so threatened that reducing human impacts alone won't save them,” lead author Kerry Stewart said in a statement. In response to follow-up questions via email, Stewart added that some species will need special recovery programs, like breeding projects and habitat restoration, to survive.

“Recovery programs are specific to individual species, so the exact intervention that is required differs,” Stewart explained. “For the critically endangered Sulu hornbill (Anthracoceros montani), it is recommended that a captive breeding program should be put in place and trees be planted to provide suitable nesting sites. For the blue-billed curassow (Crax alberti), habitat restoration and reintroduction are recommended to increase the range of the species and connect habitat fragments.”

The study estimates that, without action, 517 bird species could become extinct in the next century, resulting in a 3.2% reduction in global avian functional diversity and disrupting ecosystems that rely on birds for seed dispersal, pest control, and scavenging.

Even stopping threats entirely would only prevent half of the projected extinctions, the study found. Partial threat reduction would save just 26% of species at risk. Some, like the critically endangered Cebu Flowerpecker, with fewer than 70 birds remaining, are so depleted they’ll need direct intervention, such as captive breeding, to survive.

The study concluded that protecting habitats alone won’t save global bird diversity. While halting deforestation and pollution is vital, preventing mass extinction will require bold, species-specific interventions—and an acceptance that some losses may already be inevitable.

Stewart noted the passenger pigeon’s extinction had lasting ecological impacts: it shifted oak species' dominance, reduced soil nutrients, disrupted forest canopy cycles, and was linked to a rise in mice populations, which carry Lyme disease.

Despite such historical ramifications and dismal projections, Stewart said there is reason to be optimistic. 

“The Pale-headed brushfinch (Atlapetes pallidiceps) was thought to be extinct for 30 years but was sighted again in 1997,” Stewart noted. “The habitat where the 20 remaining breeding pairs were found was protected to prevent further habitat loss and degradation, which, alongside control of parasitic cowbirds, increased their population to over 200 and has resulted in it being downlisted from critically endangered to endangered. Sustaining conservation efforts for the Pale-headed brushfinch is essential for its continued recovery.”

Similarly, by 1982, there were only 22 California condors left and by 1987, the species was extinct in the wild. The largest bird species in North America, they have since been bred in captivity and released by the California Condor Recovery Program. As a result, there are now around 350 California condors in the wild.

However, the study also found that larger birds, such as raptors and seabirds, face the highest risk, with disproportionate losses in their ecological roles. Still, the study argues that broad conservation policies must be paired with species-specific actions to avert the worst outcomes.

For example, prioritizing the 100 most functionally unique threatened birds — such as the Andean Condor, Sulu Hornbill, and Madagascar Serpent-Eagle — could prevent 68% of projected functional diversity loss. These species are vital to ecosystems, supporting pollination, nutrient cycling and more.

Solutions may involve protecting habitats, curbing hunting and trade and investing in targeted recovery efforts for highly threatened, ecologically critical birds.

“Stopping threats is not enough, as many as 250-350 species will require complementary conservation measures, such as breeding programs and habitat restoration, if they are to survive the next century,” senior author and professor Manuela Gonzalez-Suarez said in a statement. “Prioritising conservation programs for just 100 of the most unusual threatened birds could save 68% of the variety in bird shapes and sizes. This approach could help to keep ecosystems healthy.”

Stewart said the findings show that both threat reduction and targeted recovery programmes are vital components of conservation action. 

“Given the scale of predicted biodiversity loss, it is essential to find ways to preserve ecosystem health, resilience and integrity,” Stewart said. Functional diversity provides a lens through which we can understand the role that species play in an ecosystem, to give insights into the implications of their decline.”

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