Over, Under, Around: Connecting Habitat Saves Lives
Numerous wildlife species around the world are in decline or imperiled due to habitat loss and fragmentation, much of which results from development and deforestation. Road networks span millions of miles, which divides large, contiguous areas of habitat into smaller fragments, increasing the risk of animal mortality from vehicle-wildlife collisions. Not only do these collisions claim the lives of more than one million animals per day in the United States, these events cost tens of millions of dollars in damages and injuries, and loss of human life. As human populations continue to grow, the demand for homes, businesses, and transportation networks rises, creating an increasingly more fragmented landscape where human infrastructure and wildlife needs are not always compatible. However, proactive transportation planning and habitat connectivity can improve wildlife species’ ability to navigate this patchwork landscape.
To further understand this issue, we must think about the effects vehicles and roads have on animal behavior. Naturally, wildlife response will vary by species and by individuals within a species. Roads fragment habitat and create physical barriers as well as noise barriers for animals. Some potential variables influencing animal behavior may include the width of a road, amount of traffic, the level of noise produced by the traffic, time of day of the traffic, the type and density of roadside vegetation, and the potential presence of physical barriers used to separate lanes. These factors may influence whether or not an animal attempts to cross a roadway, and if so, where they cross, and at what time of day or night crossing events occur. Wildlife mortality on roads is likely underestimated due to the quick work of scavengers, the extent of destruction of smaller animals such as frogs and salamanders, and the chance injured animals like white-tailed deer or black bear succumb to their injuries at locations out of view from the roadway.
Many times, white-tailed deer are the first species people think of when asked about vehicle-wildlife collisions in our state; however, mortality events on roads can involve a variety of species and the frequency of mortality events can vary by location and time of year. Insects such as bees and butterflies, reptiles and amphibians like salamanders, snakes and turtles, birds, small mammals including opossums and raccoons, and large mammals like black bear or elk are all subject to vehicle-wildlife collisions. With approximately 80,000 miles of state-maintained highways in North Carolina combined with projected human population growth, it’s imperative we implement effective mitigation strategies in the interest of wildlife conservation and diversity.
Why Do Animals Move?
For some of the same reasons that people do. We travel to grocery stores in search of food, go on dates in search of a potential mate, and make trips to large box stores for resources we believe will help sustain our everyday lives. Similarly, wildlife moves to fulfill life functions. Wildlife may travel in search of food, new territory, a mate, cover, water, or other habitat type. It’s important to remember that wildlife movements and the amount and type of contiguous habitat needed to meet resource requirements occur at differ ent scales and can vary temporally as well. Take for example, the differences in size of a caribou migration versus a white-tailed deer’s home range, or a field mouse’s core area of use. Each species may also have resource needs that can change daily, seasonally, or over the course of years.
Often, growth of animal populations is dependent upon or limited by the amount of available, suitable habitat, so loss of relatively small patches of land can greatly influence a species’ ability to fulfill its biological needs and survive. A number of currently threatened and endangered species rely on specific attributes of habitat to fulfill biological processes and are unlikely to increase in number unless suitable habitat is increased or the quality of habitat is improved. Fire-depend ent species are an example of wildlife that are not only depend ent on available habitat, but are dependent upon a naturally-occurring or management-induced practice to survive, which can potentially be a limiting factor for population growth or expansion. On occasion, the lack of or destruction of habitat can cause wildlife to move in search of new suitable habitat. The impacts of climate change can also require species to adapt to changing temperatures and seasonal weather patterns, which gradually impact habitat composition and can cause habitat types to shift in elevation or range, resulting in a shift of wild life inhabitants as well. Unfortunately, numerous species are becoming extinct before scientists can identify and learn about their needs in hopes of maintaining habitat and biodiversity to the extent possible.
Carving Out a Path for Wildlife
Now that we know some of the reasons why wildlife move, what can be done to help animals navigate a fragmented landscape? Habitat and connectivity hold the key. First of all, maintain- ing natural areas for wildlife through conservation easements or other land acquisition programs is a great first step. Large, contiguous tracts of land supporting unique habitat types, high biodiversity of flora and fauna, or threatened or endan gered species should be prioritized, followed by land with high potential for habitat restoration or improvement. It’s beneficial to know what species are present and this can be accomplished through surveys and monitoring. Connecting these natural areas or unique habitats through systems of corridors is an effective method to reconnect land for wild- life to travel unobstructed by roads and vehicles, reducing their risk of mortality.
So, how do corridors promote safe wildlife movement? Think of a corridor system as a network of sidewalks or green ways to ensure on-foot movement from one location to another. Linking sites together that supply the resources needed to sup port wildlife can potentially reduce or prevent genetic isolation. Many times, the use of riparian areas as corridors can support safe travel of a wide array of species. Maintaining genetic flow between disjointed sub-populations is also important to main taining healthy, sustainable wildlife populations. Wildlife can become more susceptible to extinction from naturally occurring weather events such as hurricanes and flooding when small numbers of individuals requiring specialized habitat types are restricted to small areas of suitable habitat. For example, wildlife species found only in mountain bog systems, like the bog turtle, are vulnerable to loss through habitat destruction, fragmentation due to roads, and changing hydrology or weather patterns.
When evaluating larger scale movements of species such as black bear, elk, and white-tailed deer across the landscape, one of the most cost-effective approaches is to advocate for incorporation of wildlife crossing structures in transportation planning to prevent vehicle-wildlife mortalities. Wildlife crossing structures are also beneficial to numerous smaller species including toads, salamanders, and turtles. Proactive inclusion of wildlife mitigation measures early in the planning process of roads can reduce the risk of injury and mortality to wildlife and humans alike. Strong partnerships between state and federal wildlife and transportation agencies, conservation groups, policy makers, and the public can ensure that wildlife species continue to flourish through coexistence.
Since we know different species and individuals within species respond differently to roads, solutions to ensure safe wildlife passage will also vary, and no one solution fits all. Wildlife-friendly passage structures enhance the ability of wildlife to move safely over or under roads and can be incor po rated when repairing infrastructure like on- and off-ramps and bridges. When new construction is inevitable, surveys should be conducted to identify species that will potentially cross the roads and monitoring (i.e., camera surveys, GPS or VHF tracking, or through personal observation) can identify places where wildlife are most likely to cross. Mortality ‘hot-spots’ can be identified through research and monitoring and these locations should be prioritized to receive crossing struc tures when possible. In some instances, natural landscape features or other barriers may funnel wildlife to particular places for crossing. It’s important to keep in mind that young may also travel with adults, which may require further analysis of poten tial barriers to movement. The loss of juvenile off spring or reproductive adults to mortality events can have detrimental effects on populations already struggling to maintain or expand their current numbers.
Wildlife crossing structures come in a variety of shapes and sizes and should be tailored to the species to ensure successful usage of the structures. Crossing structures can include over passes and underpasses with examples including naturally-occurring land bridges, man-made bridges with dry pathways or ‘benching’ or aquatic, free-flowing water, and various types of culverts. Also, proactive planning for implementing cross ing structures should take into account whether the structures will support terrestrial or aquatic species, or both. Use of natural substrate is best, when possible, as opposed to pave ment or concrete which may feel unnatural to animals, possibly prevent ing individuals from utilizing the crossing structures. Wildlife crossings increase in effectiveness when proper fencing and significant protected public, natural lands exist adjacent to the structures.
Fish species that spawn upriver are an example of aquatic wildlife that require free-flowing water to move from one area to another to carry out a life function intended to continue a species’ existence. If barriers such as dams exist or aquatic passageways are in danger of drying up or clogging during weather events, the fish may no longer be able to reproduce effectively. As mentioned previously, barriers can prevent genetic mixing that can result in isolated populations of species. These barriers can be geographic in nature; however, many are man-made structures such as dams or roads. While pre-project studies, implementation of crossing structures, and routine maintenance and monitoring can be expensive, these mitigation methods have been shown to be cost-effective over the long-term.
How is NCWF Helping?
As a conservation organization that values wildlife, NCWF supports habitat protection and connectivity through a variety of on-the-ground projects, partnerships, and advocacy opportunities. For the last few years, NCWF has been a partner in the Pigeon River Gorge Wildlife Connectivity Collaborative; a diverse group of biol ogists, wildlife managers, transportation planners, and wild life advocates representing state and federal agencies and non-governmental conservation organizations to name a few. The purpose of the Collaborative is to develop practical and feasible solutions to an increasing amount of wildlife mortal ity on roads in western North Carolina. NCWF staff has partici pated in the Collaborative meetings and submitted joint com ments to the NC Department of Transportation (NCDOT) on conceptual plans to upgrade highway infrastructure and will continue to assist with proactive planning for new construc tion projects to reduce wildlife mortality on roads. Elk, black bear, and white-tailed deer have been the focal species of the Collaborative; however, improvements for wildlife help small mammals, reptiles and amphibians, and aquatic species as well.
As a long-time supporter of the reintroduction of elk in the mountains of North Carolina, NCWF has maintained a lease agreement on property providing substantial benefit to elk. The current elk population consists of an estimated 200 indi vid uals and NCWF will continue to help grow these numbers through educational opportunities and events, assistance with land acquisition and connectivity, and advocating for funding to support wildlife crossings to connect elk habitat. NCWF has and will continue to support national transporta tion policy to provide increased funding for wildlife mitigation on roadways. In eastern North Carolina, NCWF partnered with the NC Wildlife Resources Commission and NCDOT to collect data from camera traps to evaluate when and how wild life utilizes highway underpasses. In addition, volunteers mon itor the wildlife underpasses and report any fence maintenance issues in need of repair and remove overgrown vegetation to ensure the crossings remains open for wildlife use.
As the state affiliate to the National Wildlife Federation, NCWF provided input that assisted with development of a formal resolution to address wildlife mortalities on roads and what can be done to mitigate these issues. The formal resolution provided recommendations to address transportation planning and funding shortcomings to ensure wildlife are able to thrive and coexist with human development. The bottom line is, how and when we travel can affect how and when animals travel. A healthy environment for humans includes healthy wildlife, plants, air, and water, which sustain life and are important to our mental and physical well-being. As humans, we’re learn ing more and more of what the resulting impacts are of not providing adequate space and connectivity for wildlife.
How You Can Help
There are many ways residents, private landowners, wildlife enthusiasts, conservation organ izations, and state and federal agencies can help reduce frag mentation and vehicle-wildlife mortality. As an individual, educating yourself on the topic and getting involved is the first step. Consider providing support to groups or agencies that are making a difference for wildlife and get involved with volunteer projects. Conservation organizations like NCWF have a grassroots-chapter network doing local habitat and wildlife projects, such as maintaining the wildlife under passes in eastern North Carolina. Advocate for wildlife by staying up-to-date on environmental policy and contact your local Congressional Representatives to voice your opinions on national legislation to provide adequate funds to support wildlife, connectivity, crossing structures and transportation planning. As a landowner, you can familiarize yourself with species on your property and make responsible stewardship and management decisions to improve wildlife habitat. When traveling, look for wildlife crossing signs. By simply slowing down in areas where wildlife is known to cross roads you can reduce the risk of a wildlife-vehicle collision. Drive safely.