Roads have become increasingly common across our globe as people utilize them to travel to places they want to go, increasing the reliability on cars for transportation needs. These large and wide networks of roads we know today severely alter a landscape and can impact wildlife in numerous ways. As seen in my previous blog posts, roads can cause impacts to wildlife such as mortality, wildlife-vehicle collisions, and limit their movement from place to place; however, roads can also shift the population demographic of a wildlife species and become a source of pollution into the environment. Roads impacts extend well beyond the surface of the road itself, causing many ecological impacts to the environment and the wildlife within it.
Habitat Fragmentation & Alteration
Roads can cause direct mortality to wildlife, causing other factors to occur such as wildlife shifting their population demographic farther away from the road, losing vital habitat space. Roads also pose a number of indirect effects onto wildlife, such as habitat fragmentation and alteration. This is due to either wildlife not being able to cross a road due to the risks of mortality or through avoiding the road altogether, shifting their habitat farther away.
Roads also create barriers that limit the movement of wildlife, one of the main issues being barriers prohibit gene flow. An example of this was seen when a group of researchers studied the genetics in timber snakes; snakes that were blocked in their movement from roads had a much lower genetic diversity than other snakes across continuous habitat types. Along with this, the male timber snakes are known to follow pheromone trails to find mates; roads disturb this trail and make it difficult for the males to be able to find mates, affecting reproduction and survival of the species.
Wildlife being affected from habitat fragmentation and alteration are also susceptible to not being able to access specific habitats. An example of this is during dry seasons; when there is a drought occurring, road prohibit wildlife from reaching vital water sources. Roads can also prevent some wildlife from reaching nesting sites, such as turtles; these species end up laying their eggs in habitats where there is more predation, meaning their is a decreased chance of reproductive success and survival of the species.
Constructing a road also alters the habitat altogether. If a road is running through a forest, the road creates an edge habitat along the parts of the road that fringe the forest itself. This can have severe consequences for wildlife, especially birds; when an edge habitat is created, birds become more susceptible to predation. This is due to predators being able to prey on birds much easier in the edge habitat, as the forest canopy at the edge offers less protection to the birds and their nests. Other wildlife susceptible to edge habitats are turtles; some species of turtle prefer to nest along edge habitats because it is an ideal habitat for their nest. However, turtles utilizing the edge habitat are now posed to a greater risk of mortality when crossing roads, and their hatchlings could also be susceptible to this when they disperse after hatching from the nest.
Pollution
While roads can alter habitats and cause fragmentation to occur, they can also channel pollutants onto the environment. Debris from tires on the road can cause things such as a decreased amount of time to metamorphosis for the wood frog species. Salt that is used to deice roads runs off the road and into adjacent ponds that can decrease the survivorship of species such as spotted salamanders and wood frogs. Deicing salts can also change frogs behavior and decrease their performance in locomotion. Frogs are one the species that have been shown to have greater skeletal abnormalities when they are closer to roads; researchers suggest this is a result from the road contamination. This is turn affects the frogs fitness, making them potentially less adept to catch prey or elude themselves away from predators.
Roads polluting the environment extend far beyond introducing chemicals into the environment; they also introduce noise and light, which can be detrimental to wildlife as well. The noise from traffic on a road can effect species of bird, causing declines in bird populations living in proximity habitats close to the road. However, not all species of bird are equally affected, such as how birds having song frequencies similar to that of a car frequency being found as absent from habitats near roadsides. Noise from a road can also change bird species’ community composition, meaning that some species of birds are differentially excluded from a particular habitat near a road.
Along with noise polluting the environment, light can as well. Some species of wildlife rely on light to control biological activities, and this can be impacted by lights along a road. For example, robins use sunlight as a cue to begin their morning songs and can mistake lights on a road for the sun and begin their song in the middle of the night. Lights from roads can also alter flying routes for bats, as well as expose some frog species to artificial light during the night that could delay their metamorphosis time. Along with this, sea turtle hatchlings use light in order to navigate themselves to the sea and can become confused by lights on a road and go toward a road instead of the ocean; this can cause the hatchlings to die from dehydration, predators, and /or wildlife-vehicle collisions, and they will never reach the ocean. This goes for the females that nest their hatchlings as well, sometimes becoming disoriented from road lights and have a difficult time getting back to the ocean.
A final note on pollution from roads is that is can facilitate the spread of invasive species when land is cleared for a road. An example of this was seen in Australia with cane toads; these species of toad are very invasive in the continent and use roadside areas to move, causing an increase in their range as a population. Along with this, species such as fire ants may also build their mounding nests by areas cleared for roads because this is an ideal habitat for them. Roads can facilitate the invasion of invasive species, and alter or fragment a habitat; all of this impacts are detrimental to both wildlife and the land they live in.
Mitigation Strategies
There are numerous solutions and mitigation strategies being developed to help decrease the amount of harmful impacts our roads cause to wildlife. In instances where the pattern of mortality can be predicted for a specific are during a specific time of year, roads are either closed or reduced in their speed limits to decrease the rates of wildlife mortality. Another solution is creating artificial nesting sites for gravid species that need them; this can reduce species from needing to potentially cross a road, the distance they need to travel, and/or their chances of mortality.
A main issue with roads is the traffic volume on them. Though decreasing traffic volume is not very likely to be effective for a mitigation strategy, constructing alternative methods to cross a road could become more successful. For example, culverts can be used for smaller animals to allow for a safe passage under a roadway; this has been shown to be highly effective in decreasing mortality rates of wildlife. For bigger animals, overpasses can be used to cross a road; this overpass would need to have specific features of the wildlife’s environment, such as vegetation planted over it to mimic the habitat type.
There are many factors that need to be taken into consideration when ensuring wildlife can effectively and efficiently cross our road structures. We need to implement and create new ways to protect and preserve our wildlife, as well as the environment they live in. From this post, we have learned that roads not only impact wildlife through things such as mortality or vehicle collisions, but roads also create very real and severe threats to the environment that in turn affect wildlife. We as humans have a job of conserving our planet, and that includes the wildlife within it. Without the wildlife, there would not be an environment for us to destruct upon, as wildlife naturally disperse seeds, nutrients, and vital resources the environment needs to keep going.
“We are part of the environment, just as much as wild animals are. They do not seek to kill us, we seek to kill them. It’s surely our responsibility to do everything within our power to create a planet that provides a home not just for us, but for all life on Earth.” – David Attenborough.
