Are animal bridges actually helping wildlife conservation?
Sydney Riedel
The fight for wildlife conservation has been a long uphill battle against the construction of roads, and it’s been suggested that a solution has been found. Wildlife crossing bridges and tunnels have been implemented for a variety of species in different areas of the world. These seemed to be an easy fix for roads disrupting habitats, but a paper published in 2023 in the Journal of Applied Ecology points out the lack of research behind these mitigation measures.
Roads vs. Animals
As the development of roads increases, the stress on the natural environment grows, especially for the wildlife living in the area. A major problem from this is called the “barrier effect,” which implies that animal movement decreases due to roads, thus affecting the population. The barrier effect can cause resources which were once accessible to be limited, population demographics to be impacted, changes in seasonal migrations, and even a loss of genetic variation. These matters prompted the study and implementation of methods which would allow animal movement across roads.
The most famous of the solutions are wildlife overpasses and underpasses, where bridges and tunnels are meant to be a continuation of the natural ecosystem over or under a road. These structures are often now part of the approval process for new roads. With their popularity there is an assumption around them that they are effective and successful with the conservation of local wildlife.
Misconceptions About Wildlife Crossings
The authors of the paper “Do wildlife crossing structures mitigate the barrier effect of roads on animal movement? A global assessment” conducted studies of literature and research which claims to demonstrate the evidence supporting these structures. They found the wildlife crossing structures have not been properly evaluated nor established correctly. It was stressed that without comparisons of the conditions and movements before the construction, the end results of the structures can be less effective than they seem. Essentially, if data is collected after the installation of a bridge and it shows wildlife moving over it frequently, then it appears to be successful. However, there is the possibility of wildlife movement being much more frequent and necessary before the road was built, and now the population is declining even with the bridge. The main concern is people believing a lot more wildlife is being conserved than actually is, and species are being put under more pressure than what scientists believe.
The Science Behind it
There have been a multitude of studies conducted focusing on the wildlife crossing structures. The authors specified their criteria for animal bridges or tunnels which crossed roads. They then picked apart each study, finding major flaws and biases which were common occurrences. The major bias was an experiment which compared a control group, where no crossing was built, to an impact group where a crossing was built. The problem was the two groups not having equal amounts of animal movement in them, skewing the results of the experiments. The standout flaw though is the number of studies done on the wildlife crossings which compare the results to the pre construction conditions, which is barely any. The difficulty of accomplishing this is recognized, since researchers would have to know where construction is taking place and how long they have before it begins. With that being said, it is still imperative that there is extensive research to determine the performance of wildlife crossing structures.
The article describes how future projects on bridges must aim to prevent a decline in cross-road movement for wildlife, since as of right now the number of studies which fail to do so is quite high. It should be abundantly clear that full restoration is not a guarantee with the crossings, even with them being a requirement for construction projects.
The World is in Need of More Science
This research on pre-existing studies pointed out a field of study in which the scientific community is lacking. Habitat degradation and fragmentation is happening at an extremely fast pace, and wildlife is constantly dealing with the consequences. It can be dangerous for conservation scientists to use research with such concerning flaws as it can have direct impacts on wildlife. Studies about the bridges do seem reliable and thorough, making it more urgent for this information to be known and spread. Wildlife is extremely important to the human population as they help sustain the ecosystem and natural world which humans depend on for food, medicine, energy, and much more. As human caused alterations put large stressors on wildlife, it is necessary to input more time and resources into areas where further evidence is crucial for survival of the natural world.
Citations
Soanes, Kylie, et al. “Do wildlife crossing structures mitigate the barrier effect of roads on animal movement? A global assessment.” Journal of Applied Ecology, 29 Jan. 2024, https://doi.org/10.1111/1365-2664.14582.
