There are about 50 billion birds on Earth – about six per person. This arises from the extrapolation of Australian scientists. According to this, there are only a few species with more than a billion specimens, while many species are rare or very rare.

Birds that remain popular include the sparrow and barn swallow, and the rare kiwi fruit bird. The researchers say that knowing the frequency of a species is important for timely conservation measures.

The study, led by the team led by William Cornwell of the University of New South Wales (UNSW) in Sydney (Australia) is presented in the journal Proceedings of the US National Academy of Sciences (“PNAS”). The researchers combined scientific surveys of individual species in specific distribution regions with nearly one billion entries in the Internet “eBird” database. About 600,000 citizen scientists enter to watch birds in it.

Cornwell and colleagues used the research data to determine their estimated number of occurrences per unit area for 724 species. They compared this to the frequency with which these species were seen on eBird. They also considered how often humans were likely to spot a bird species based on its appearance and lifestyle. Birds breeding near settlements are more often spotted than those mostly in remote areas.

From these specifications, the researchers developed an estimate of the global frequency of 9,700 bird species—about 92 percent of all known bird species. The remaining eight percent were not included in the estimate due to unconfirmed data. However, since they are all rare species, their number hardly adds to the total number of birds, the researchers explained.

According to their calculations, there are only four species, of which there are more than a billion individuals: house sparrow or sparrow (Passer localus; 1.6 billion), starling (Sturnus vulgaris; 1.3 billion), ring-beaked gull (Larus) delawarensis; 1.2 billion) and the barn swallow (Hirundo rustica; 1.1 billion).

There are only about 100 samples of chicken Tornex melanogaster left. About 12 percent of the species have a population size of less than 5,000 animals, including the extremely rare amber tern (Thalasseus bernsteini), long-bellied bushbird (Atrichornis clamosus), which is thought to be extinct, and the flightless rail drum (Habroptila wallacii).

The researchers write that measuring the abundance of a species is a critical first step in its conservation. “By calculating correctly what’s present, we learn which species may be susceptible and can see how these patterns change over time,” explains first author Cory Callahan from the University of New South Wales. The researchers investigated whether the rare occurrence was typical of certain groups of birds, but were unable to find a general pattern. The least common were birds from the kiwi family (3000) and substrate claws (154,000).

Diet data was also collected for the study: so most of the birds living today eat invertebrates such as worms (15 billion), but many are also omnivores (13 billion). The rarest scavengers (194 million) and birds that live on flower nectar (479 million).

The researchers write that how these and other numbers develop can be recorded every five to 10 years. “If their population declines, it could be a real wake-up call for the health of our ecosystem,” Cornwell points out. The researchers hypothesize that their method could also be used for other animal species. They also advocate that as many interested lay people as possible serve as citizen scientists. “It can be as simple as checking to see if you can see something outside the window while having your morning coffee,” Cornwell says.

© dpa-infocom, dpa: 210518-99-638010 / 4 (dpa)