Ishikari plain and Ishikari river on Hokkaido, Japan – a region that has lost many birds in 150 years
Masayuki Yamashita / Alamy
More than 70 per cent of birds – and a similar proportion of bird species – have disappeared in a region of Japan once occupied by hunter-gatherers and converted into farmland only a century and a half ago.
The Ishikari Lowland in north-west Japan was still inhabited by hunter-gatherer communities until the 19th century. Using old and new maps to trace changes in the landscape since wide-scale farming began there in 1869, researchers have discovered the “surprising” disappearance of a high proportion of forest and wetland birds in the area – and their partial replacement by crows, larks and other birds that thrive in croplands and rice paddies, says Munehiro Kitazawa at Hokkaido University in Japan.
“This is definitely globally relevant,” says Chase Mendenhall at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, who wasn’t involved in the work. “There’s a lot to be learned about how biodiversity responds, reacts and is resilient to change.”
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The Ainu, an Indigenous people in Ishikari, and their ancestors lived off salmon, deer, bear and edible plants for approximately 15,000 years. Agricultural landscaping, including systematic deforestation and wetland drainage, only began in the region after the Japanese government stepped in. Today, the land is a mix of agricultural plots and housing developments, representing a dramatic change in land cover in only 153 years.
Kitazawa’s previous research explored the way native Japanese birds seek habitats in abandoned lands, and he wanted to know how they coped with the changes in Ishikari. “I couldn’t stop imagining, ‘How many wildlife species or individuals were there before broad-scale conversion to farmland, and how many have we lost?’” he says.
Globally, scientists have lacked reliable data about the effects of agriculture on wildlife in the northern hemisphere because hunter-gatherer communities had vanished from many regions long before early researchers began documenting wildlife, he says. But Japan has kept “fine-scale” topological data on its territories since the 1850s – which covers the final years before Ishikari’s conversion to farmland.
In addition, explorers had already visited and described the region in published literary works, says Kitazawa. Those explorers had described “dense forests”, filled mainly with alders and Japanese elms, and large wetlands marked by common reed and sedges.
Armed with this information, Kitazawa and his colleagues divided the 8400-square-kilometre Ishikari Lowland region into 2-hectare plots and studied the land cover of each one through time using maps from 1850, 1880, 1900, 1950, 1985 and 2016. Then, having determined the changes in land cover of each plot, they took advantage of their previously validated bird population model, which generates data according to land cover type, to estimate bird species and abundance. This allowed them to estimate the changes to the bird communities across the decades since the region’s hunter-gatherer days.
They estimate that oriental turtle doves (Streptopelia orientalis), great spotted woodpeckers (Dendrocopos major), Japanese tits (Parus minor) and other forest-dwelling birds have lost approximately 90 per cent of their populations in Ishikari since the change in land cover, says Kitazawa. Swinhoe’s rails (Coturnicops exquisitus), lanceolated warblers (Locustella lanceolata), reed buntings (Emberiza schoeniclus) and other species that thrive in wetlands experienced similar losses.
Although grassland species like Japanese quail (Coturnix japonica) and Stejneger’s stonechat (Saxicola stejnegeri) increased in numbers at the start of the agricultural shift in Ishikari, they too were calculated to have declined by a net 68 per cent relative to their pre-agricultural numbers as the grasslands gave way to more croplands, rice paddies and even urban housing developments in the 2000s, says Kitazawa.
Populations of birds that thrive on agricultural lands, including carrion crows (Corvus corone) and Eurasian skylarks (Alauda arvensis), are estimated to have increased by an average of 50 per cent in the region, says Kitazawa. Even so, that didn’t compensate for the total loss in abundance of birds in the region. The calculations suggest the current bird abundance is less than a third of what it was prior to the switch to farming, he adds.
“I think the most surprising and the most important part [of this study] is just the sheer amount of nature that has been lost in terms of abundance,” says Mendenhall.
For Laura Kehoe at the University of Oxford, it is “unique” to see “such an interesting case study” dealing with such a rare opportunity for data. “We just don’t see this kind of story happening everywhere else, because so many areas have been converted so long ago,” says Kehoe.
“To me, the study speaks to something that’s already quite clear, to be honest,” she says. “And that’s that industrial agriculture does not benefit the natural world.”
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2022.0338
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