Survey: Drastic decrease in Japan’s wild bird population

Courtesy of Hiroshi Uchida
A swallow

The populations of common wild birds, such as sparrows and swallows, has significantly decreased over the past 20 years, according to a nationwide survey.

The decline is thought to be mainly the result of a decrease in the number of insects, resulting in less food. Experts said there is a possibility that people don’t see the common wild birds around them, and their actual population size needs to be assessed.

The survey, which was organized by the Environment Ministry’s Center for Biological Diversity, the Wild Bird Society of Japan and other groups, is conducted about once every 20 years. It is the third survey of its kind, following the 1974-78 and 1997-2002 studies.

About 2,000 researchers and volunteers observed birds in 2,344 locations nationwide from 2016-21. Researchers also collected information, including where chicks were heard, using questionnaires.

Courtesy of Toshifumi Miki

The survey confirmed 379 wild bird species. Comparing 1,947 locations from previous surveys, the swallow population decreased by 40% to 8,987, and the sparrow population decreased by 34% to 20,627. There was also a decrease in cattle egrets and starlings.

The results suggested that the populations of wild birds that prefer open spaces or catch their prey midair particularly decreased. Mutsuyuki Ueta, 51, president of Bird Research, a nonprofit organization that took part in the survey, said the decline might be the result of a decrease in the insect population and large farmlands, where some birds like to hunt.

Courtesy of Toshifumi Moriya
A red-billed leiothrix

However, among invasive bird species that are subject to extermination, the Chinese thrush population grew 20-fold to 1,105, and the red-billed leiothrix population increased 2.4-fold to 1,507. These birds are thought to have been initially kept as pets but were abandoned or escaped and bred in the wild.