Wildlife Corridors: Helping Animals Cope With Human Sprawl
Habitat fragmentation is the spatial separation of land that was once connected. In my last post in this series I discussed the role of roadways in habitat fragmentation. In the United States, the vast highway system cuts off many animals from safe paths to migrate, forage, hunt, or escape danger. Wildlife corridors have been proposed, and occasionally used, as a solution to this problem. In this post I will discuss wildlife corridors and their efficacy with respect to providing safe passage over or under highways.
Wildlife corridors are stretches of land or other constructed environments that serve as pathways between otherwise disconnected areas of land. In the case of corridors for avoiding highway traffic, some are intentional and some are not. Drainage ditches, for example, were not built for the purpose of allowing animals safe passage, but animals use them to avoid the highways nonetheless. In one study, researchers monitored 15 underpasses and drainage ditches beneath highways in Los Angeles, California, and found that they “were used by a variety of species, including carnivores, mule deer, small mammals, and reptiles.”
Although less common, some wildlife corridors are created with the express intent of providing a safe way for animals to bypass traffic and humans. One of the biggest efforts in this regard is Banff National Park in Canada, which has gone to great lengths to provide corridors for wildlife throughout the park’s 2,500-plus square miles. Though this is one of the most extensive efforts, it is not by any means the only effort for wildlife crossings. From Turkey to India to Tanzania and throughout the rest of the world, communities are working to mitigate the negative impact that human sprawl is having for other species.
One reason that these corridors are not more prevalent is that planners must first justify the cost by proving they are effective. Overall, there is some evidence that these corridors are used, though there remains debate about whether or not they are cost-effective. However, if you were one of the animals that doesn’t end up as “road kill” because of such a corridor, obviously you would think it well worth the cost. It seems to me that it should be the duty of humans to mitigate the effects of their environmental take-over, no matter the cost, so I will focus only on the research that discusses efficacy rather than cost-effectiveness.
So, are corridors effective? The simple answer is yes, but there are mitigating factors. These corridors must be developed in ways that respond to the needs of animals of each area specifically, and in such a way that their use is encouraged. The aforementioned study conducted in California found that even when corridors are not intended for animals, they will use them for safe passage. But they also found that other factors influenced their use. Specifically, the type of habitat immediately on each side of these corridors needs to be suitable for the animals who will use it. These authors suggest that along with building corridors, there should be a focus on habitat restoration on either side of the corridor. In addition, fencing should be put in place to help animals avoid highways and direct them toward the corridors.
Researchers David Lindenmayer and Henry Nix, in their review of studies on the topic, found that the width of the corridor, habitat in and around the corridor, and other factors related to animals’ diets, foraging patterns, and social structure also affected how and if the corridors are used by animals. Although this is an older study (published in 1993), their findings are still instructive as there has not been widespread progress in building wildlife corridors in the past two decades.
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Similarly, researchers studying Banff National Park in Canada found the corridor by itself was not sufficient to guarantee use by animals. This study as well found that the habitat surrounding the area of the corridor is of significant importance. They also found that different factors mattered for different species of animals. This highlights the need for planners to be aware of the specific environment in which they are building roads and corridors so that the needs of the animals who live in that area can be attended to. It may also suggest that multiple corridors, with the needs of different species of animal in mind, could be useful in some areas.
The most important finding of this study, however, is that human activity has an impact on corridor use. Carnivorous animals in particular were found to be less likely to use corridors in the presence of human activity. Along with the development of more wildlife corridors, it is therefore also important that human activity is controlled to allow other animals safe spaces.
The take-home lesson here is that humans need to be much more conscious of how and where we expand. In the U.S., less than 5% of land is protected by the National Parks Service. And even this does not guarantee a lack of human intervention as park visitors and even hunters are allowed in much of this area. We are taking over more and more space that others—plants and animals—need to survive. We not only need to mitigate the consequences of human growth and infrastructure, as wildlife corridors seek to do, but we must also try to limit our expansion and impact on the environment and other animals moving forward.