What’s Driving Bird Declines In Europe?
It’s no secret that human activity negatively impacts wild animals. From climate change to urbanization to intensive agriculture, it can be hard to work out which species are affected the most by different human pressures. What’s more, research has found that some pressures can affect certain animals negatively while providing benefits to others.
This study used data from 170 bird species across 28 European countries to understand how human pressures affected bird populations from 1980-2016. The authors analyzed existing research including national species-monitoring data and “bird surveys” completed by citizen scientists throughout Europe. They were interested in understanding the impacts of four major human impacts on the environment:
- Climate change (measured by average temperature change)
- Intensive agriculture (measured by how much land is made up of farms with high volumes of pesticides and fertilizers)
- Urbanization (measured by the area of land covered by towns and cities)
- Change in forest cover
In addition to ranking which pressures had the most negative impacts for bird populations overall, the authors aimed to understand the dynamics of how each pressure affected different birds depending on their traits (e.g., woodland birds vs. cold-dwelling birds, or generalists vs. specialists). For example, increased temperatures may be especially harmful for birds who thrive in colder climates.
The study found that bird numbers declined by about 25% in the countries surveyed. Farmland birds were most affected, and the authors noted that both farmland and cold-dwelling birds declined in almost every country included in the data. The pressures causing these declines differed by country — for example, the authors note that birds in Western Europe were more impacted by urbanization than those in Eastern Europe.
The main pressure affecting bird decline was intensive farming. Urbanization also had a negative effect, while the effect was different for changes in forest cover and climate change. For example, the time series data revealed that many bird species were impacted positively as well as negatively from both of these pressures, while the trends analysis revealed that climate change had an overall negative impact.
Birds aren’t a homogenous group, and the authors recognized this through their analysis of bird traits. They found that the four human pressures impacted birds differently depending on certain characteristics, such as their diet or habitat. For example, birds who relied partially or fully on invertebrates for their diet tended to experience negative effects from all four pressures. Meanwhile, hot-dwelling and urban-dwelling birds experienced positive effects from increasing temperatures associated with climate change, while cold-dwelling and farmland bird species were impacted negatively.
Large studies like this one provide strong evidence of the harms humans are having on wild animals. Climate change and urbanization are bad for birds, but pesticide and fertilizer use is having a greater impact. The authors note that we need more research on the impacts of pesticides and fertilizers on bird populations. However, we do know that pesticide use can kill insects, in turn reducing birds’ food supply, or build up in their system, ultimately harming the birds who eat them.
In addition to raising awareness of the link between human activity and bird declines, animal advocates can use this research in their legislative advocacy. For example, shifting away from intensive, monoculture crop systems and avoiding harmful pesticides and fertilizers can support wild insect populations, in turn supporting the birds who rely on them.
https://www.pnas.org/doi/10.1073/pnas.2216573120