Global Bird Population
Recent studies suggest that the total bird population on our planet ranges from 50 billion to 430 billion.
Inspiration Behind the Study
In 2015, biologist Corey Callaghan was in a northern Everglades marsh, captivated by a massive flock of tree swallows. This spectacle sparked a question in his mind: just how many birds are there in the world?
Initial Count
Motivated by this awe-inspiring experience, Callaghan started his quest by estimating the number of birds in the flock he had just observed. He calculated over half a million birds by taking photographs, counting birds in different segments of the image, and then extrapolating the total.
Estimating Global Bird Population
Despite the challenges, Callaghan and his team from the University of New South Wales in Sydney, Australia, embarked on this ambitious project. Their research, which was the first of its kind, estimated that there are likely between 50 billion and 428 billion birds on Earth.
Challenges in Estimation
This wide range is due to several uncertainties, including the difficulty of counting billions of small, mobile creatures, the vast and often indistinct territories birds inhabit, and the lack of scientific data in many parts of the world.
Methodology
Their groundbreaking study, published on May 17 in the Proceedings of the National Academy of Sciences, employed a unique methodology. It combined data collected by both professional scientific organizations and citizen scientists, covering 92 percent of all bird species in the world.
Importance of Biodiversity
For Callaghan, this endeavor was long overdue. He believes that while we invest a lot of time and effort in counting humans, it’s equally important to keep track of the biodiversity we share our planet with.
Abundance and Rarity of Bird Species
The paper reveals that the most abundant bird in the world is the house sparrow, with a population of 1.6 billion. Following closely are the European starling (1.3 billion), ring-billed gulls (1.2 billion), barn swallows (1.1 billion), glaucous gulls (949 million), and alder flycatchers (896 million).
The researchers found that there are only a few super-abundant species, and many more rare ones, which is a common pattern in ecology. They estimate that 1,180 bird species—12 percent of the world’s total—each have a total population below 5,000.
Endangered Species
If a species has a total population under 2,500, the International Union for Conservation of Nature would label it an endangered species. These rarities include species like the great spotted kiwi (estimated population: 377 individuals), the Javan hawk eagle (630), and the Seychelles kestrel (under 100). The tree swallows, which sparked Callaghan’s curiosity, number around 24 million.
Comparison with Domestic Birds
For comparison, the estimated world population of domestic chickens is somewhere around 25 billion, making them the most abundant bird by far. However, this study only looked at wild birds.
Decline in Bird Population
It’s unclear how many birds the world has lost in the past few decades, but this study helps provide an estimate to establish a baseline. One 2019 paper calculated that the total population of breeding adult birds in North America has declined by 3 billion since 1970.
Novelty of the Study
The novelty of this study is the way it combines professional and citizen science data. Lucas DeGroote, a researcher at the Carnegie Museum of Natural History’s Powdermill Avian Research Centre, praises the study for its ambition and precision.
Nature’s Fragility
The researchers used estimates from three datasets produced by experts around the world for the scientific organisations Partners in Flight, the British Trust for Ornithology, and BirdLife International. They combined those data with observations from eBird, the world’s largest database collected by citizen scientists—in this case, amateur birdwatchers.
The researchers admit there is a lot of uncertainty inherent in their estimates. But part of the study’s strength is that it quantifies this uncertainty, and provides wide ranges of possible populations for thousands of birds, says Thomas Brooks, chief scientist with the International Union for Conservation of Nature.
Interpreting the Data
Ken Rosenberg, a conservation scientist at the Cornell Lab of Ornithology, thought the study was “a bold attempt.” But he urges caution in interpreting the data, because there is so much variability and uncertainty in the estimates.
Importance of Conservation
For Brooks, the paper illustrates just how precious many bird species are, and how close they could come to the brink if new threats emerge. DeGroote concurs, emphasizing the importance of knowing how many of a species there are and what the trend is for effective conservation.