No fewer than 50 billion birds call planet Earth home, according to an extrapolation by Australian scientists published in the journal Proceedings of the U.S. National Academy of Sciences on Tuesday.
This means that there are about six times as many birds as humans on the planet.
A team led by William Cornwell from the University of New South Wales (UNSW) in Sydney worked with data on 9,700 known bird species from around the world, which they said represented 92 per cent of all extant species.
The researchers combined scientific surveys of individual species in certain distribution areas with the almost one billion entries in the online ornithological database eBird.
The researchers concluded that there are comparatively few common species, and many rare species.
Among the top 10 most abundant birds in the world are the house sparrow (1.6 billion), the european starling (1.3 billion), the ring-billed gull (1.2 billion) and the barn swallow (1.1 billion).
The researchers found that the least abundant orders of birds in the world were flightless kiwis from New Zealand (3,000) and mesites (154,000), scrubland birds endemic to Madagascar.
“There are a considerable number of individual birds in the world of 50 billion, but fully understanding why and how they all arrived at their current population sizes will be paramount to the future study of evolution, ecology, and conservation,’’ the researchers said in a statement.