Soaring populations put four species in ‘billion bird club’

·2 min read
A mumuration of starlings swoop over marshlands in Somerset. The species is one of four to number over a billion individual birds
A mumuration of starlings swoop over marshlands in Somerset. The species is one of four to number over a billion individual birds

Four bird species regularly seen in the UK have been found to be members of an exclusive "billion club", with a study has showing their populations number more than one billion.

Ring-billed gulls, house sparrows, European starlings and barn swallows have been identified as the most prolific birds out of a total of 9,700 different species.

Researchers say there are roughly 50 billion individual birds in the world – a figure that outnumbers humans by six to one – and the unprecedented counting each species is the "crucial first step" in conservation efforts to help birds most under threat of extinction.

Dr William Cornwell, an ecologist at the University of New South Wales in Australia, said: "Humans have spent a great deal of effort counting the members of our own species – all 7.8 billion of us. This is the first comprehensive effort to count a suite of other species.

"We'll be able to tell how these species are faring by repeating the study in five or 10 years. If their population numbers are going down, it could be a real alarm bell for the health of our ecosystem."

The total number of individual birds in the world is dominated by only a few species - Steve Parsons/PA
The total number of individual birds in the world is dominated by only a few species - Steve Parsons/PA

The research team reached the figures by pooling together almost a billion bird sightings logged on eBird, an online database of bird observations from hobbyists. The study dataset includes records for almost all – 92 per cent – bird species currently alive.

However, the researchers say it is unlikely that the remaining eight per cent, which were excluded for being so rare that there was a lack of available data, would have much impact on the overall estimate.

Using this data and some detailed case studies, they developed an algorithm to estimate the actual global population of each bird species. Only four types of bird were found to have populations of over one billion, making them part of a so-called "billion club".

Those most prolific species included the house sparrow, at 1.6 billion, the European starling, at 1.3 billion, the ring-billed gull, at 1.2 billion, and the barn swallow, at 1.1 billion.

Dr Corey Callaghan, the study's lead author, said: "It was surprising that only a few species dominate the total number of individual birds in the world. What is it about those species, evolutionarily, that has made them so hyper-successful?

"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 findings are being published in the Proceedings of the National Academy of Sciences.

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