Data collected by 600,000 citizen scientists around the world has been used to calculate how many birds and bird species there are on Earth.
The new study, which aims to help conservation efforts, estimates there are 50 billion individual wild birds and more than 9,700 different bird species in the world.
The research team at the University of New South Wales used professional scientific and citizen science datasets to develop a statistical model to estimate individual bird species' populations in a world-first study.
Findings show there are about six birds per human being on the planet, but many species are rare and there are only four species with a population greater than one billion.
Birds of the so called "one billion club" are the house sparrow, European starling, ring-billed gull, and barn swallow.
Associate Professor Will Cornwell of the University of New South Wales said birds like the house sparrow were specialists in living in human-dominated environments while others were native to specific ecosystems.
"Humans dominate quite a lot of the land surface so the house sparrow has a close relationship with the houses people build, they do really well in those environments.
Some of the most common species in Australia are the native rainbow lorikeet with a population of 19 million, followed by the sulphur-crested cockatoo at 10 million and the laughing kookaburra at 3.4 million.
Urbanisation, climate change, and agriculture
Climate change is one of the major threats to biodiversity losses across all plant and animal species on the planet, and birds are not an exception.
The increased conversion of natural habitat for agricultural use and urban environments poses another major risk to bird populations, according to Mr Cornwell.
In Australia, bushfires like the devastating Black Summer fires in 2019/2020, which burned more than 12.6 million hectares across the country, are amid the biggest concerns.
It is estimated almost 3 billion animals were killed or displaced, including 180 million birds.
Mr Cornwell said events like the Black Summer fires were going to become increasingly common and that was why it was important to understand more about its effects on biodiversity.
Citizen science crucial to research
To create the statistical model for their study, the research team used bird observation data recorded by more than 600,000 citizen scientists.
The sightings were logged between 2010 and 2019 on eBird, one of the largest global citizen science projects managed by the Cornell Lab of Ornithology.
Mr Cornwell believed a decade ago they would not have been able undertake their study.
"The world is a big place and it's just not possible for professional scientists to get to all those places where there is important biodiversity frequently enough to do that monitoring.
"That's were citizen scientists can really step in and fill a really crucial role."
While the team is confident in their findings, they acknowledged a range of uncertainties when working with large scale datasets and global estimates.
"The biggest challenge was citizen science is not as systematic as professional science data … so we had to come up with a way to estimate the relationship between more systematic and less systematic data," Mr Cornwell said.
Moving forward, the team aims to improve the modelling and repeat their bird population documentation in the coming years to record changes in individual bird species.
"To find out if they are [bird populations] increasing or decreasing is really important for conservation and understanding how our planet is doing," Mr Cornwell said.
