Gray wolves were locally extinct in Germany since the 1800s, but recently have successfully recolonized the northeastern region of the country by crossing the border from Poland. More than 100 wolf packs were counted in 2019. This is an impressive feat, but one obstacle stands in the way of a robust wolf population in the country — vehicle collisions.
Road accidents account for more than 75 percent of all known wolf mortality in Germany. Fortunately, realizing the enormous benefit to both humans and wildlife that comes from reducing animals in roadways, efforts have been made around the world to build “green bridges.” These bridges provide wildlife with safe crossing opportunities over roads and highways, helping them move freely throughout the landscape.
The novelty of these bridges means that researchers are still testing out if, and how, different wildlife species will utilize them. Will prey species be deterred if they sense that predators use the same crossings? Will animals use the crossings during the day, when noise from the road is peaking, or merely at night when human disturbance is lower? These and other questions led researchers to examine one such green bridge built over a highway connecting Berlin to Poland.
Using camera traps, which monitor the activities of animals with motion-activated photos and videos, researchers determined that wolves actively use the green bridge to safely cross the highway, and that their presence doesn’t seem to deter deer and boar (their main prey) from using the same crossing. First constructed in 2012, when wolves were still absent from the region, the bridge has quickly become a known safe crossing destination for wolves. The first wolf crossing was recorded in late 2015, and the wolves used the bridge over 85 times the following year. The bridge is one of seven such green bridges throughout the German state of Brandenburg.
The results from this study help wildlife biologists determine the myriad benefits of green bridges. Wolves use the bridges more frequently during the winter months, which could be due to the seasonal need to expand their hunting range. In contrast, deer and wild boar tend to cross more in the spring and summer. All species crossed the bridge more during dawn and dusk, and least often during the day, when human activity is highest.
These analyses of species use of green bridges and other wildlife crossings are important for understanding how we can best design and implement them. Studies like this can help determine where to place green bridges in the landscape to optimize their use by wildlife species and maximize the benefit to humans by keeping animals out of the roads, facilitating our coexistence as we endeavor to lighten our footprint on the landscape.