A new study of global bird populations, based mainly on citizen science databases such as eBird, estimates there are around 50 billion wild birds in the world.

Four species, according to the study, have a population of more than one billion birds. On the other hand, about one-tenth of the bird species in the world have fewer than 5,000 individuals. 

A team of researchers at the University of New South Wales conducted the study, which was published in the “Proceedings of the National Academy of Sciences.” The researchers adjusted the citizen science numbers by modeling and consulting birding experts in specific regions.

So what are the four members of the billion bird club? Two of them are rather obvious: house sparrow and European starling. House sparrows, according to the study, are the world’s most populous bird with 1.6 billion individuals. The other two species were less obvious, to me anyway: ring-billed gull and barn swallow. I see a lot of ring-billed gulls pretty much everywhere I go in New England (inland and shore), but I didn’t realize they had such a global presence as well. 

Barn swallow was the one that really surprised me. Not to be a bird snob, but house sparrows, starlings and ring-billed gulls are not what I would consider to be desirable birds. In the case of house sparrow and starling, they are non-native birds that have thrived in North America at the expense of native birds. Barn swallows, in my estimation, are desirable birds and I enjoy seeing them in the field. It was good news to me that this study put the barn swallow in the billion bird club.

I have no reason to doubt these researchers, but I did want to cross reference that number with other recent similar studies. Determining the global population of 9,700 bird species is a tall task and by no means an exact science. Heck, getting a perfectly accurate count of the birds in your own backyard is pretty much impossible. 

Past studies have estimated the global bird population to be anywhere from 200 to 400 billion individual birds. That’s a wide range and not even close to the 50 billion birds estimated by this recent study.

I also found that past studies have estimated the global barn swallow population to be somewhere between 100 million and 200 million. BirdNote, the popular radio program and website, included in an episode that the “worldwide population of barn swallows is estimated to be 190 million.” The bird conservation consortium Partners in Flight estimates a breeding population of 120 million barn swallows. 

So what is it? One billion (or more), 190 million (or less), or somewhere in between? It depends on the study, obviously. Either way, it’s good to see that the barn swallow population is thriving. Or is it? 

A 2014 article published by phys.org claims that the barn swallow “has seen a 95 percent drop in numbers across North American in the last 40 years.” The article opens by defining the word “extinction,” and hints that swallows may be heading in that direction. 

One billion individuals or teetering on extinction? That’s a huge difference, but both extremes are reported by seemingly credible sources. I’m sure each research team will vehemently defend their own numbers — at least I hope they would.

A 2019 study of birds in the Western Hemisphere by Cornell Lab of Ornithology, American Bird Conservancy, Smithsonian Conservation Biology Institute and other organizations, garnered a lot of attention and press, and was hailed as a wake-up call to protect birds before they disappear. The study found that one in four birds had disappeared over the last 50 years. This study estimated the barn swallow population in the Western Hemisphere to be around 46 million birds.

The wide-ranging numbers underscore how difficult it is to get an accurate count of global bird populations. Personally, I like to go with the lower estimates. I think there’s no doubt that birds and other wildlife are in decline to some degree. Why not take steps to change that? If we are wrong and the population is thriving, well, then we’d just have more of a good thing.