In one of the biggest data studies of its kind ever carried out, researchers have put a figure on how many wild birds are inhabiting the planet right now – so before we tell you, make a guess and see if you were anywhere close.

Ready? The official tally is roughly 50 billion, over six times as many as there are humans on our planet. That covers a total of 9,700 bird species (92 percent of those alive today), from the avocet to the zebra finch, and is based on over a billion sightings logged on the citizen science portal eBird.

Those data were combined with actual case studies and a scaling algorithm to estimate the number of birds on the planet as a whole, with allowances made for species that are more likely to be spotted than others.

"Humans have spent a great deal of effort counting the members of our own species – all 7.8 billion of us," says ecologist Will Cornwell, from the University of New South Wales (UNSW) in Sydney in Australia. "This is the first comprehensive effort to count a suite of other species."

Some species, like the black-breasted buttonquail, only have around 100 birds left. For other species, such as the rainbow lorikeet, the numbers are in the many millions. Four species were in the 'billion club': the house sparrow, the European starling, the ring-billed gull and the barn swallow.

That only a few species dominate bird populations is surprising, the researchers say. Future studies could look into some of the possible reasons why these types of birds have evolved to be so dominant. On the flip side, around 12 percent of bird species have estimated global populations of less than 5,000.

This sort of study wouldn't be possible without the citizen science data collected over the internet, the team behind the study acknowledges. Data from some 600,000 contributors to eBird were used during the course of the research, and scientists are encouraging more people to get involved in logging their bird sightings.

"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 biologist Corey Callaghan, from the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig in Germany.

The researchers flag in their paper that there is a level of uncertainty in their figures, unavoidable for a host of reasons – from how regularly certain species are sought out by birdwatchers, to annual patterns of migration. The 50 billion number is actually the median average from the estimates generated by the study, with the mean average coming in at 428 billion.

"Currently, our approach is limited by the training data used in our analyses, and increasing the number of training species will likely improve the certainty of abundance estimate for a number of species," the team writes in their study.

To help get an even more accurate bird count, the scientists are hoping to repeat the research every few years. That should show population change over time, and will be important for another reason: conservation.

"Our approach allows for these data to be easily quantified, providing global estimates per taxonomic clade," the researchers write.

Repeating the study regularly will enable experts to see how specific species are doing over time, and it's part of the reason that the contribution from members of the public is so important. While birdwatching is a popular hobby in countries like the US and the UK, other nations are less well covered.

"Quantifying the abundance of a species is a crucial first step in conservation," says Callaghan.

"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 research has been published in PNAS.