Agricultural intensification is the main cause of a dramatic decline in birds in Europe. They are some 20 million to disappear on average each year, conclude researchers in an article published Monday, May 15, after having amassed an unprecedented extent of data.
Many European scientists, who publish in the American journal PNAS (Proceedings of the National Academy of Sciences), collaborated on this study with the aim of determining which human activities are responsible for the decline of European bird populations.
To do this, they used a dataset unprecedented in its scope: 37 years of observations from 20,000 ecological monitoring sites in 28 European countries, for 170 species.
"There has been a one-quarter decline in species abundance since 1980," Vincent Devictor, a CNRS researcher and coordinator of the study, told AFP. "In other words, 800 million individuals in 40 years, or 20 million per year, so a systemic, profound decline in European avifauna," says the expert.
The use of pesticides and fertilizers affects the survival of birds
Some ecosystems are more severely affected than others: the number of forest birds has decreased by 18%, to 28% for urban birds and even 57% for birds in agricultural areas.
"We conclude that agricultural intensification, particularly the use of pesticides and fertilizers, represents the main pressure for most bird population declines, especially those that feed on invertebrates," the scientists write in their paper.
These invertebrates represent, in fact, "an important part of the diet for many birds during at least some stages of their development," point out the authors.
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They are thus crucial for 143 species among the 170 studied during the breeding season. A reduction in the food available will, for example, have a negative effect on reproductive success by changing the behaviour of parents and affecting the survival of chicks. The decline is marked in species such as the grey flycatcher (-63%) or the famous house sparrow (-64%).
To stop this collapse, we would have to start by changing the model of agriculture. However, "we continue to be in an industrial vision of the agricultural world", associating massive recourse to mechanization and chemistry, regrets Vincent Devictor, who highlights the increase of megafarms in France to the detriment of small areas.
Concretization and disappearance of insects in cities
In addition to agriculture, other factors related to human activity are also affecting bird populations, starting with climate change.
Logically, it hits hard species preferring cold (40% decline), such as the boreal, but does not spare heat friendly species (18% decline).
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Finally, the progression of urbanization is also claiming victims among swifts and swallows. "We are creating territories that are increasingly hostile, including the interior of the urban environment," says Vincent Devictor, who worked with two colleagues based in France, PhD student Stanislas Rigal and Vasilis Dakos of the CNRS.
"Species liked to nest in crevices, to be in places where there are still insects in urban areas. With the modes of concretization today, coupled with the disappearance of insects, it becomes hostile even for them," he says.
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