Through Adam vaughan

Earth is home to around 50 billion wild birds according to a new global estimate, but most species are very rare and only a few billion.

Only four non-domesticated species are in the club of those numbering over a billion individuals, along with house sparrows (Passer domesticus) the most abundant, followed by European starlings (Sturnus vulgaris), ring-billed gulls (Larus delawarensis) and barn swallows (Hirundo rustica). In contrast, 1,180 species have fewer than 5,000 birds each.

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“One of the takeaways is that Mother Nature just loves rare species. This is what some call hyper dominance, which has been found in the flora of Amazonian trees and other groups of plants. It’s not very surprising, but it’s good to have the data, ”says Corey Callaghan of the University of New South Wales, Australia, who led the research.

The estimate of about six wild birds for every human on the planet is the first since researchers arrived at a global figure of 200 to 400 billion non-domesticated birds 24 years ago. The large gap between studies is not due to a dramatic drop in bird numbers, but is due to a more sophisticated method that uses data for more species.

Callaghan and his colleagues took citizen science data on bird sightings from the eBird online database to build a model estimating global numbers of species. To make sure it worked well, they crossed the results of 724 species with other sources of rigorous data on well-studied birds. The model was then extrapolated to 9,700 species, reaching a median of 50 billion wild birds worldwide.

The citizen science observations that underpin the research are both its strength and its weakness, says Richard Gregory of the UK charity Royal Society for the Protection of Birds. eBird has much less data on birds in the tropics than in temperature regions, he says.

For example, the red-billed quele is sometimes considered the most numerous undomesticated bird on the planet, but in the new analysis, its population is estimated at just 95 million.

Another example is that the model initially predicted a best estimate of around 500 live ivory-billed woodpeckers, although this species is believed to be extinct. This quirk was caused by two erroneous observations of the species in the database during upload, which were later deleted by reviewers. Nonetheless, Callaghan says that such granular differences for individual species do not change the overall estimate.

Callaghan says we could improve bird conservation with more research into why certain species are rare, whether it is simply because they have evolved to occupy a single island or due to human activities such as deforestation. .

Journal reference: PNAS, DOI: 10.1073 / pnas.2023170118

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