The causes behind the bird population decline include wind turbines, urbanization, loss of habitat, light pollution, climate change, hunting and even cat predation. The multitude of these potential causes has been an excuse for political inaction for a long time. But unprecedented European studies published on Monday, May 15 in the Proceedings of the National Academy of Sciences, the official journal of the American National Academy of Sciences, largely dispel the convenient excuse of "multiple causes." For the first time, these studies have established a basic hierarchy of causes driving down bird populations in Europe and highlight the use of pesticides and synthetic fertilizers as the major contributor, ahead of global warming.
"The tremendous negative impact of agricultural intensification on birds has long been reported in particular for farmland and insectivorous birds, but our study provides strong evidence of a direct and predominant effect of farmland practices at large continental scales," the authors wrote. This means that agricultural intensification, in particular the use of synthetic inputs such as pesticides and fertilizers, is the major cause of the decline of many bird species present in agricultural and non-agricultural areas.
The index created by researchers shows that the Netherlands, the Czech Republic, Ireland and France have seen the highest increase in agricultural intensification in recent years.
The decline in the number of European birds is staggering. It is a total decrease of 25% for all species monitored over the 37-year study, even when taking into account the increase in the populations of species that proliferate when in contact with human activities. In total, there are around 800 million fewer birds than there were 40 years ago. The decline in farmland species is a shocking 60%. The number of urban birds has declined by an average of 28% and the number of woodland birds has dropped by 18%.
Pressure fluctuations
To conduct their analysis, researchers used the most comprehensive data available from the PanEuropean Common Bird Monitoring Scheme. More than 20,000 sites in 28 European countries were monitored using standardized protocols and the presence of 170 different species was regularly monitored.
To determine the major causes of this rapid decline, around 50 European researchers, led by Vincent Devictor, Stanislas Rigal and Vasilis Dakos, collected these data and compared them with indicators of changes in the four major anthropogenic pressures on ecosystems: climate change, urbanization, forest cover and the use of fertilizers and pesticides. "We were not satisfied with measuring correlations between these indicators and variations in the evolution of bird populations. We assessed causal links using recent mathematical analysis techniques that are rarely used to study biodiversity," explained biologist Vincent Devictor, a researcher at the National Center for Scientific Research at the Institute of Evolutionary Science of Montpellier (ISEM) and co-author of this study.
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