How many birds are there in the world? More than 600K citizen scientists helped to find out

A flock of cockatiels are seen in this undated photo. (Corey T. Callaghan)

TORONTO — In a monumental effort, Australian researchers have attempted to estimate how many birds there are in the world using observation data from more than 600,000 citizen scientists.

According to the research, published in the Proceedings of the National Academy of Sciences on Tuesday, there are approximately 50 billion individual birds in the world – or about six birds for every human on the planet.

“Humans have spent a great deal of effort counting the members of our own species - all 7.8 billion of us,” Will Cornwell, an ecologist at University of New South Wales Science and co-senior author of the study, said in a press release.

“This is the first comprehensive effort to count a suite of other species.”

As far as bird species, the UNSW study found there were an estimated 9,700 different kinds, including flightless birds, such as emus and penguins.

Of those species, only four had the distinct honour of being a part of what the researchers dubbed “the billion club,” meaning they had an estimated global population of more than a billion. These species included the House Sparrow (1.6 billion), the European Starling (1.3 billion), Ring-billed Gull (1.2 billion), and Barn Swallow (1.1 billion).

“It was surprising that only a few species dominate the total number of individual birds in the world,” study lead author Corey Callaghan, who completed the research while he was a postdoctoral researcher at UNSW Science, said.

“What is it about those species, evolutionarily, that has made them so hyper-successful?”

The dataset for the study included records for nearly all (92 per cent) bird species currently alive. The remaining eight per cent, according to the researchers, were excluded for being so rare there was a lack of available data on them.

In order to calculate these population estimates, the researchers used nearly a billion bird observations recorded by birdwatchers between 2010 and 2019 on the online database eBird, one of the world’s largest biodiversity-related science projects, which is run by The Cornell Lab of Ornithology.

They combined this data with detailed case studies and developed an algorithm to estimate the actual global population of each bird species. This calculation also took into account each species’ “detectability,” meaning how likely it was the bird was spotted by someone and recorded on eBird, the researchers said.

“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,” Corey Callaghan, who is now based at the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, said.

Why did these researchers feel it was important to estimate the population of birds in the world? Callaghan said it was 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,” he said.

And although 50 billion is a lot of birds, not all species are thriving as well as those in “the billion club,” the scientists warned. Some species, including Chinese Crested Tern, Noisy Scrub-bird, and Invisible Rail, have estimated global populations of less than 5,000.

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