Scientists calculate how many individual birds there are in the world, and it’s a lot

I just stepped outside my house and counted two roadrunners, three starlings, five house sparrows and one house finch. Based on my calculations, there are a lot of birds in the world, but you don’t have to listen to me. Researchers ran the numbers and figured out there are over 50 billion birds living on our planet.

“Humans have spent a great deal of effort counting the members of our own species — all 7.8 billion of us,” ecologist Will Cornwell in a University of New South Wales said in a statement. “This is the first comprehensive effort to count a suite of other species.” Cornwell is a co-author of the bird-count study published in the Proceedings of the National Academy of Sciences journal on Monday.

It took the efforts of hundreds of thousands of people to help reach the 50 billion bird number. The researchers used nearly a billion observations contributed to the eBird database by over 600,000 citizen-scientists between 2010 and 2019. From there, computer algorithms took over.

The team worked the numbers on 9,700 species of birds, which is about 92% of all living bird species, creating estimates for each population based on the eBird data along with calculations on the birds’ “detectability.” “Detectability can include factors like their size, color, whether they fly in flocks, and if they live close to cities,” UNSW said.

The data pointed to a select few species that belong to “the billion club” of birds with an estimated global population topping a billion. Those abundant birdies are the house sparrow, European starling, ring-billed gull and barn swallow. That explains the starling and sparrow sightings just outside my house.

The study also highlighted species with low estimated population numbers, including the Chinese crested tern and noisy scrub-bird. “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.”

The team emphasized the numbers are estimates and there is still “considerable uncertainty.” They didn’t go out and count every single bird — that would be impossible. Relying on bird-watchers means there are some weaknesses in the numbers, particularly on regions where eBird isn’t used as much. 

“Our findings, while rough in some areas, represent the best-available data we currently have for many species,” said co-author Shinichi Nakagawa, a UNSW ecologist and statistician.

The researchers hope more people will get involved with birding and logging their avian observations through eBird. It can be as easy as getting to know the birds that hang around your home. Lead author Corey Callaghan said, “You can usually find a bird or two to identify and watch anywhere you go, anytime of the day, anywhere in the world.”