“Humans go to great lengths to count the members of our own species, the 7.8 billion people in the world,” reflects Will Cornwell, an ecologist at the University of New South Wales (Australia) and author of a work by big data that has just been published in PNAS that concludes that there are 50 billion birds in the world. The study bases its findings on citizen science observations and various algorithms, and has included 9,700 species of birds, including flightless ones like emus and penguins.
A global effort thanks to birders from all over the world
Birdwatching is a hobby that is gaining adherents and thousands of people, professionals or amateurs, are used to walking with their binoculars around their necks and making notes of the species they see on their journeys. Taken together, this huge amount of data collected on an individual basis can provide invaluable information, but is often left isolated in field notebooks. So far: The growing popularity of citizen scientist websites and apps has made bird watching an accessible way to interact with science.
This is the case of eBird , an online database that collects observations of birds from around the world, and whose data the Australian team used to collect almost a billion bird sightings and develop an algorithm that estimated the world population of each species . The information was provided by more than 600,000 bird fans between 2010 and 2019.
This calculation took into account the “detectability” of each species, that is, the probability that a person detected this bird and submitted the sighting to eBird . Detectability can include factors such as their size, color, whether they fly in flocks, and whether they live near cities. “While this study applies to birds, our large-scale data integration approach could act as a model to calculate species-specific abundances for other groups of animals,” explains study lead author Corey Callaghan. “Quantifying the abundance of a species is a crucial first step in conservation. By properly counting what’s out there, we learn which species may be vulnerable and we can track how these patterns change over time.”
The study data set includes records for almost all bird species (92%) currently alive. However, the researchers say the remaining 8%, which was excluded as so rare that no data was available, is unlikely to have a large impact on the overall estimate.
‘The billion club’
Only four species of birds belonged to what researchers call “the billion club” – species with an estimated global population of more than a billion. The house sparrow ( Passer domesticus : 1.6 billion) heads this exclusive group, which also includes the European starling ( Sturnus vulgaris : 1.3 billion), the ring-billed gull ( Larus delawarensis : 1.2 billion) and the barn swallow (Hirundo rustica 1.1 billion).
On the other hand, about 12% of the species studied have an estimated world population of less than 5,000 individuals: the Chinese crested tern ( Thalasseus bernsteini ), the noisy scrub bird ( Atrichornis clamosus ) and the invisible rail ( Habroptila wallacii ) are Some examples. ” We can see how these species are doing by repeating the study in five to 10 years, ” Cornwell explains.
While the team is confident in their estimates, they recognize that a degree of uncertainty is inevitable when working with large data sets like this one. For example, people documenting sightings are more likely to look for rare species. “You need a range of uncertainty when making estimates at the global level,” says Professor Shinichi Nakagawa, an ecologist and statistician who co-authored the paper.
“We will need to repeat and refine this effort to truly control biodiversity, especially as human-caused changes in the world continue and intensify,” adds Callaghan.
