Facts: 170 species
The study includes data on 170 bird species collected by volunteers within the framework of the equivalent of Swedish Bird Taxation, in 28 European countries over a period of 36 years. According to the researchers, it is the world’s largest collection of data in the field.
Four human impact factors were studied: agriculture, urbanization, warmer climate and changes in forest cover.
All factors have clearly contributed to the decline in bird populations except for that concerning forest cover, where the relationships are more unclear.
There is less and less chirping in Europe. Bird numbers on the continent have declined by between 17 and 19 percent since 1980, a loss of between 560–620 million birds, according to an earlier estimate.
But why? An international research team has tried to get to the bottom of this by analyzing a large amount of data, which has been collected by thousands of volunteers, so-called citizen researchers, in Sweden and 27 other European countries during the period 1980–2016.
According to the results, which are published in the journal PNASthe increasingly intensive agriculture is the main cause of the shrinking bird populations.
It is especially agriculture’s use of pesticides and fertilizers that hits the birds hard, including by affecting the insects they feed on. But the researchers do not yet know exactly what these connections look like.
Birds that disappeared in Europe between 1980–2016.
Martin Green, an ecologist at Lund University and one of the people responsible for Swedish bird taxing, thinks it is an interesting study that for the first time shows the harmful effects of modern agriculture on birds on a continental scale.
“It strengthens the image that we already had on a smaller scale,” writes Green in a comment to TT.
Also affects urban sheep shines
Agriculture is not only the biggest threat to birds that are linked to agricultural land, in Sweden for example song lark and starling, but also to other species.
“It leads to a negative impact on bird species in general, which has probably not been shown before,” writes Green.
Agricultural birds decreased by 57 percent during the study period, urban birds by 28 percent and forest birds by 18 percent.
Today, 40 percent of Europe’s surface is used for agriculture, often with little biological diversity. In addition to pesticides and fertilizers, the leveling of the landscape is something that affects the birds, points out Martin Green.
Second only to agriculture, the increasing urbanization was the factor that had the greatest significance for the birds becoming fewer. The warmer climate has also contributed, although it has favored some more heat-loving varieties.
The swallow is one of many bird species that have a tough time in Sweden. Upswing in Sweden
In Sweden, many bird species have declined in the last 40–50 years, and the agricultural birds are the ones that have fared the worst even here.
In the last decade, however, slightly more species have increased in number than decreased, although in most cases it is a matter of a small recovery. In general, larger birds such as raptors and geese are doing better, while smaller species such as barn swallows and barn owls are in decline.
At the same time, more and more bird species are redlisted. Of the 245 species that breed in Sweden, a quarter are estimated to have declined so sharply that they have been red-listed, including a number of “common” species such as the birch thrush and bittern.