Eagles are often drawn to roads and railways, lured by the availability of road-killed animals as a food source. However, this behavior is increasingly leading to them being struck by vehicles. A new study from the Swedish University of Agricultural Sciences (SLU) shows that eagles have changed their behavior in search of food and that this often leads to death. They fall into a so-called ecological trap.
Using data from 74 GPS-tagged golden eagles, researchers have been able to track the movements of the eagles between 2010 and 2020. The study shows that eagles across the country actively choose to concentrate near railways and roads because there is plenty of food there.
- Eagles have simply learned to select these habitats due to the thousands of roadkill that remain. These places become attractive to the eagles because they don't need to expend energy hunting, but at the same time, it becomes a trap when they risk being hit, says Navinder Singh, Associate Professor at the Department of Wildlife, Fish, and Environmental Studies at SLU in Umeå.
He explains that an eagle that is startled wants to fly towards an open area rather than into the forest. If they are startled near a railway or road, they fly directly into the traffic instead.
Statistics from the National Wildlife Accident Council show that 650 golden eagles and white-tailed eagles died in traffic between 2010 and 2023. At the same time, the statistics only show reported eagles, so there is a hidden figure.
In the study, which was published in Science of the Total Environment, researchers found that the risk of dying was 5.5 times higher for eagles that chose to live along roads and railways than for those that lived and foraged in other areas.
- We also saw that young eagles were more likely to choose road-killed animals as food. Many of them end up in accidents and this could have major consequences for the population in the future, says Navinder Singh.
In an earlier study, the same research team looked at dead eagles and found that those killed in traffic accidents had higher levels of lead in their livers. The lead came from ammunition that the eagles ingest when they eat carcass remains. The study showed that the eagles' movement behavior and flight capacity were altered by lead poisoning.
- Eagles with lead in their blood loose coordination and ability to fly, which increases their risk of collisions, says Navinder Singh.
The researchers concluded that several measures are needed to reduce the risk of eagles dying in traffic accidents. It is also an issue that affects management across Scandinavia, as eagles move between countries and behave similarly in Norway and Finland.
When wildlife accidents occur, carcasses must be removed from roads and railways as soon as possible to avoid attracting eagles, for example, but they are often left in inaccessible places. At the same time, several attempts are being made to reduce wildlife accidents by, for example, scaring animals away from roads and railways.
- To get rid of the ecological trap, we need to ensure that there are fewer wildlife accidents, but also review the use of lead ammunition, says Navinder Singh.
The golden eagle project has been partly funded by the EU's Interreg Aurora programme.
Eagles are attracted to train tracks where roadkill has been left. Illustration: Michelle Etienne
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Navinder J. Singh, Michelle Etienne, Göran Spong, Frauke Ecke, Birger Hörnfeldt
Linear infrastructure and associated wildlife accidents create an ecological trap for an apex predator and scavenger
https://www.sciencedirect.com/science/article/pii/S0048969724070918
Navinder Singh. Photo: Frida Wengberg.
When we humans change landscapes and environments, we can create places that become attractive to different species. For example, the availability of food or warmth can be attractive. But at the same time, the environments pose dangers and animals risk being killed.
An example of a man-made ecological trap is artificial light that attracts species that think it is the sun or moon.
