Through a combination of citizen science and big data analytics, researchers have estimated the entire global population of birds. There are roughly 50 billion individual birds chirping and flapping across the world, about six birds for every human.
“Humans have spent a great deal of effort counting the members of our own species – all 7.8 billion of us,” says Associate Professor Will Cornwell, an ecologist at the University of New South Wales and co-senior author of the study.
“This is the first comprehensive effort to count a suite of other species.”
In order to estimate the number of birds in the whole world, the researchers in Australia pooled together almost a billion bird sightings from eBird, an online database of bird observations curated by citizen scientists and run by the Cornell Lab of Ornithology. Over 600,000 people contributed information to the database. This data included the species of bird, the location of the sighting, the size and color of the individual, whether or not it was close to a city, and other factors that were used to calculate a species’ ‘detectability’ — a measure of how likely it is for a person to spot a particular bird.
There are over 9,700 different bird species that we know of, and the eBird catalog covers 92% of these species. The remaining 8% of species are very rare species that are rarely sighted, meaning their numbers are very low so their exclusion from the analysis shouldn’t have much impact on the overall estimate.
While some species are threatened with extinction others are incredibly abundant. In fact, four bird species are in what researchers call ‘the billionaire club’, due to having an estimated population of over a billion. These include the house sparrow (1.6 billion), followed by the European starling (1.3 billion), ring-billed gull (1.2 billion), and barn swallow (1.1 billion).
But while a select few of ‘one percenters’ dominate the ecosystems, many others are struggling to survive. Around 12% of bird species included in the study have an estimated population numbering less than 5,000, making them extremely vulnerable to extinction. These include birds such as the Chinese Crested Tern, Noisy Scrub-bird, and Invisible Rail.
The researchers plan on doing a follow-up study a decade from now to see how the most vulnerable species fare in the meantime. If these populations fare worse, it could be a real alarm bell for the health of their native ecosystems.
Naturally, this assessment isn’t definitive since it relies on extrapolating sightings. Some of these sightings may be inaccurate, but at least some degree of uncertainty is to be expected when working with very large, global datasets such as eBird.
“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,” says study lead author Dr. Corey Callaghan, who completed the research while he was a postdoctoral researcher at UNSW Science.
“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 researchers would like to invite any birdwatching enthusiast to contribute to eBird. As more data becomes available, the researchers plan to perform more robust analyses that may paint a more accurate picture of the state of bird ecosystems across the globe. Ultimately, this information will greatly inform conservation efforts to direct resources where they’re the most needed.
“A great starting point is to learn a handful of birds that come to your local area, like Rainbow Lorikeets, Sulphur Crested Cockatoo, and Australian White Ibis,” Cornwell says.
“It can be as simple as seeing if you can spot any out the window while you’re drinking your coffee in the morning.”
The findings appeared in the Proceedings of the National Academy of Sciences.