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Birds outnumber people six to one with a global population of 50 billion

A new big data study from UNSW Sydney has calculated that there are 50 billion birds in the world, which is about six birds for every human. By combining citizen scientist observations with detailed algorithms, the experts estimated the number of birds that belong to 9,700 different bird species worldwide.

The researchers found that many iconic Australian birds are numbered in the millions, including 19 million Rainbow Lorikeets and 10 moon Sulphur-crested Cockatoos. By contrast, the rare Black-breasted Buttonquail is down to around 100 individuals.

“Humans have spent a great deal of effort counting the members of our own species – all 7.8 billion of us,” said study co-senior author Professor Will Cornwell. “This is the first comprehensive effort to count a suite of other species.”

The study was focused on almost a billion bird sightings documented on eBird, an online database of bird observations from citizen scientists. The researchers developed an algorithm to analyze the data and estimate the global population of each species.

“While this study focuses on birds, our large-scale data integration approach could act as a blueprint for calculating species-specific abundances for other groups of animals,” said study lead author Dr. Corey Callaghan.

“Quantifying the abundance of a species is a crucial first step in conservation. By properly counting what’s out there, we learn what species might be vulnerable and can track how these patterns change over time – in other words, we can better understand our baselines.”

The dataset included records for 92 percent of all existing bird species. The experts noted that it is unlikely the remaining 8 percent, which are extremely rare,  would have much impact on the estimate.

Four bird species belong to what the researchers call “the billion club,” which are species with an estimated global population of over a billion. The House Sparrow came out on top with 1.6 billion individuals, followed by the European Starling, the Ring-billed Gull, and the Barn Swallow.

“It was surprising that only a few species dominate the total number of individual birds in the world,” said Dr. Callaghan. “What is it about those species, evolutionarily, that has made them so hyper-successful?”

Overall, about 12 percent of bird species analyzed for the study have an estimated global population of less than 5,000, including the Chinese Crested Tern, Noisy Scrub-bird, and Invisible Rail.

“We’ll be able to tell how these species are faring by repeating the study in five or 10 years,” said Professor Cornwell. “If their population numbers are going down, it could be a real alarm bell for the health of our ecosystem.”

The study was made possible with the help of more than 600,000 citizen scientists who recorded their sightings in the eBird dataset between 2010 and 2019. The eBird site is run by the Cornell Lab of Ornithology, and the data is freely available.

“Large global citizen science databases such as eBird are revolutionising our ability to study macroecology,” said Professor Cornwell. “This type of data simply wasn’t available a decade ago.”

The research is published in the Proceedings of the National Academy of Sciences.

By Chrissy Sexton, Staff Writer

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