Abundance of bird species, from large to small

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Large species are rare, new study found, but those with fewer individuals are abundant

Credit: Jen Christiansen (graphic), Liz Wahid (birds)
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Comparing the relative sizes of bird species has long seemed an impossible task – too many species simply lack reliable counts. A recent influx of citizen science data, however, has allowed researchers to make estimates of global abundance for 9,700 species, or about 92 percent of all birds on Earth. Biologists Corey T. Callaghan, Shinichi Nakagawa and William K. Cornwell, all from the University of New South Wales in Australia, combined scientific data from 724 well-studied species with counts from the eBird app, where the people all over the world can submit bird sightings. The researchers used an algorithm to extrapolate the estimates for all species in their sample. The results, recently published in the Proceedings of the National Academy of Sciences UNITED STATES, confirm a common pattern in animals: across the world there are many species with small isolated populations in niche habitats and relatively few species that have managed to spread over a large area and increase their populations in hundreds of millions or billions. Ultimately, the results could aid conservation efforts. “The next step is to find out which species are rare because this is how Mother Nature created them, and which species are rare because we [humans] Fucked up? ”Callaghan asks. This project didn’t attempt to answer those questions, but it’s a“ necessary first step ”to getting there, he says.

The graph groups bird species by population size and shows circles to scale according to the number of species in each group.
Credit: Jen Christiansen (graphic), Liz Wahid (birds); Source: “Global Abundance Estimates for 9,700 Bird Species”, by Corey T. Callaghan, Shinichi Nakagawa and William K. Cornwell, in PNAS, Flight. 118, 25 May 2021 (The data)

This article originally appeared under the title “Counting Birds” in Scientific American 325, 2, 84 (August 2021)

doi: 10.1038 / scientificamerican0821-84



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