In 2015, in northern Florida’s Everglades, biologist Corey Callahan watched a gigantic swarm of tree tanks salute the morning sun. When the mass of birds passed high above his head, he and his partner could only watch in awe. And they wondered how many birds this flock contained. As well as the number of birds that fly around the earth.
“It was an amazing experience,” says Callahan. Inspired by this view, he began counting the number of birds in the large flock of tree tanks: he reached more than half a million specimens. He was able to make his calculations thanks to the photographs he took of the squadron, which allowed him to count individual samples in static portions of pictures and then expand the numbers.
Census of all birds on Earth is of course more complicated, but years later Callaghan was the first to compute a dangerous total, albeit by a large margin between the minimum and maximum estimate. In a new study, published on May 17th in Proceedings of the National Academy of Sciences Callaghan and two other researchers at the University of New South Wales in Sydney estimate that there are likely to be between 50 and 428 billion birds flying or walking on Earth.
The margin of error is very wide due to the presence of many uncertain variables. For example, it is difficult to count billions of small birds that spread their wings over very large and sometimes unknown areas. Often little research has been done in the distribution areas of these birds, which are spread all over the world.
The researchers used a unique method in which they combined data collected from professional scientists and ordinary citizens. This allowed them to include 92 percent of all known bird species in the world.
The study is the first serious attempt to estimate the total number of birds on Earth by species. For Callaghan, it is time to do this kind of research: “We pay a lot of attention to counting people, but we also have to closely monitor the biodiversity with which we share the planet.”
From finches to large gray kiwi
According to the study, the most abundant bird in the world is the common house sparrow, with a population of 1.6 billion individuals. In second place are the starlings (1.3 billion), followed by the ring-beaked gull (1.2 billion), the barn swallow (1.1 billion), the great mayor (the gull type; 949 million), and the songbird alder flycatcher (896 million). ).
Scientists are not surprised that only a handful of bird species exist in huge numbers and the rest live in much smaller groups, because this is a known pattern in the environment. In all, they estimated that of 1,180 bird species (12 percent of the global total), fewer than 5,000 fly or walk on Earth.
If the total number of bird species consists of less than 2,500 individuals, then the International Union for Conservation of Nature talks about the endangered species.
These very rare birds include the Great Gray Kiwi (estimated population: 377), the Javan Crested Eagle (630) and the Seychelles Kestrel (<100). Among the tree trees that originally prompted Callahan to enumerate, the study found that there are about 24 million of them flying around the world.
If you compare these numbers with the total number of chickens in the world, about 25 billion, then this domesticated bird is the most common species on Earth. But the study only looked at birds in the wild.
It’s unclear how many birds the world has lost in the past few decades, but new research may help establish a baseline for that. A 2019 study calculated that the total number of nesting birds in North America has decreased by three billion since 1970.
The original approach to the new study is to combine data from academics and ordinary citizens, says Lucas DeGroot, a researcher at the Powdermill Bird Research Center at the Carnegie Museum of Natural History.
“It’s an ambitious approach and a big task to find out how many birds there are in the world now,” says DeGroote. “They thought about it very carefully and it took a lot of steps to make the estimate as accurate as possible.”
