Roadkill
Roadkill is a wild animal that has been killed by collision with motor vehicles. Wildlife-vehicle collisions have increasingly been the topic of academic research to understand the causes, and how they can be mitigated.
History
Essentially non-existent before the advent of mechanized transport, roadkill is associated with increasing automobile speed in the early 20th century. In 1920, naturalist Joseph Grinnell wrote of his observations in the state of California that "this is a relatively new source of fatality; and if one were to estimate the entire mileage of such roads in the state, the mortality must mount into the hundreds and perhaps thousands every 24 hours."In Europe and North America, deer are the animal most likely to cause vehicle damage.
Causes
The development of roads affects wildlife by altering and isolating habitat and populations, deterring the movement of wildlife, and resulting in extensive wildlife mortality. One writer states that "our insulated industrialized culture keeps us disconnected from life beyond our windshields." Driving "mindlessly" without paying attention to the movements of others in the vehicle's path, driving at speeds that do not allow stopping, and distractions contribute to the death toll. Moreover, a culture of indifference and hopelessness is created if people learn to ignore lifeless bodies on roads.Intentional collisions
A study in Ontario, Canada in 1996 found many reptiles killed on portions of the road where vehicle tires do not usually pass over, which led to the inference that some drivers intentionally run over reptiles. To verify this hypothesis, research in 2007 found that 2.7% of drivers intentionally hit reptile decoys masquerading as snakes and turtles. Several drivers were seen to speed up when aiming for the decoys. Male drivers hit the reptile decoys more often than female drivers. However, 3.4% of male drivers and 3% of female drivers stopped to rescue the reptile decoys.Road salt accumulations
On roadways where rumble strips are installed to provide a tactile vibration alerting drivers when drifting from their lane, the rumble strips may accumulate road salt in regions where it is used. The excess salt can accumulate and attract both small and large wildlife in search of salt licks; these animals are at great risk of becoming roadkill or causing accidents.Distribution and abundance
Very large numbers of mammals, birds, reptiles, amphibians and invertebrates are killed on the world's roads every day. A Humane Society volunteer survey conducted over three Memorial Day weekends in the 1960s estimated that one million vertebrate animals are killed by vehicular traffic daily in the United States. A 2008 Federal Highway Administration report estimates that 1 to 2 million accidents occur each year between large animals and vehicles. Extrapolating globally based on total length of roads, roughly 5.5 million vertebrates are killed per day, or over 2 billion annually.The estimated number of birds killed on the roads in different European countries ranges from 350,000 to 27 million, depending on the factors such as the geography of the country and bird migration paths.
Species affected
Mortality resulting from roadkill can be very significant for species with small populations. Roadkill is estimated to be responsible for 50% of deaths of Florida panthers, and is the largest cause of badger deaths in England. Roadkill is considered to significantly contribute to the population decline of many threatened species, including wolf, koala and eastern quoll. In Tasmania, Australia the most common species affected by roadkill are brushtail possums and Tasmanian pademelons. In Bolivia there has been a report of an Andean cat, a critically endangered species, dead by a car collision.In 1993, 25 schools throughout New England, United States, participated in a roadkill study involving 1,923 animal deaths. By category, the fatalities were: 81% mammals, 15% bird, 3% reptiles and amphibians, 1% indiscernible. Extrapolating these data nationwide, Merritt Clifton estimated that the following animals are being killed by motor vehicles in the United States annually: 41 million squirrels, 26 million cats, 22 million rats, 19 million Virginia opossums, 15 million raccoons, 6 million dogs, and 350,000 deer. This study may not have considered differences in observability between taxa, and has not been published in peer-reviewed scientific literature. Observability, amongst other factors, may be the reason for mammal species dominating roadkill reports, whereas bird and amphibian mortality are likely underestimated.
A year-long study in northern India in an agricultural landscape covering only 20 km of road identified 133 road kills of 33 species comprising amphibians, reptiles, birds and mammals. The study compared road-killed animals with all species seen along the road and estimated that traffic killed individuals of 30% of amphibian species, 25% of reptile species, 16% of birds, and 27% of mammals that were seen in the area.
Insects
A 2007 study showed that insects, too, are prone to a very high risk of roadkill incidence. Research showed interesting patterns in insect roadkills in relation to the vehicle density.The decrease in insects being killed by cars is known as the "windshield phenomenon". In 2003–2004, the Royal Society for the Protection of Birds investigated anecdotal reports of declining insect populations in the UK by asking drivers to affix a postcard-sized PVC rectangle, called a "splatometer", to the front of their cars. Almost 40,000 drivers took part, and the results found one squashed insect for every driven. This contrasts with 30 years ago when cars were covered more completely with insects, supporting the idea that insect numbers had waned.
In 2011, Dutch biologist Arnold van Vliet coordinated a similar study of insect deaths on car license plates. He found two insects killed on the license-plate area for every driven. This implies about 1.6 trillion insect deaths by cars per year in the Netherlands, and about 32.5 trillion deaths in the United States if the figures are extrapolated there. The number grows to 228 trillion per year if extended globally.
Scavengers
One rarely considered positive aspect of roadkill is the regular availability of carrion it provides for scavenger species such as vultures, crows, ravens, foxes, opossums and a wide variety of carnivorous insects. Areas with robust scavenger populations tend to see roadkilled animal corpses being quickly carried off, sometimes within minutes of being struck. This can skew data and cause a lower estimation of the number of roadkill animals per year. In particularly roadkill-prone areas, scavenging birds rely on roadkill for much of their daily nutritional requirements, and can even be seen observing the roadway from telephone poles, overhead wires and trees, waiting for animals, usually squirrels, opossums and raccoons to be struck so they can swoop down and feed. However, such scavengers are at greater risk of becoming roadkill themselves, and are subject to evolutionary pressure to be alert to traffic hazards.In contrast, areas where scavengers have been driven out often see roadkill rotting in place indefinitely on the roadways and being further macerated by traffic. The remains must be manually removed by dedicated disposal personnel and disposed of via cremation; this greatly increases the public nuisance inherent to roadkill, unnecessarily complicates its disposal, and consumes additional public money, time and fuel that could be spent on other roadway maintenance projects.
Research
Roadkill observation projects
The study of roadkill has proven highly amenable to the application of citizen science observation methods. Since 2009, statewide roadkill observation systems have been started in the US, enrolling hundreds of observers in reporting roadkill on a website. The observers, who are usually naturalists or professional scientists, provide identification, location, and other information about the observations. The data are then displayed on a website for easy visualization and made available for studies of proximate causes of roadkill, actual wildlife distributions, wildlife movement, and other studies. Roadkill observation system websites are available for the US states of California, Maine, and Idaho. In each case, index roads are used to help quantify total impact of vehicle collisions on specific vertebrate taxa. Researchers that use data from citizen science platforms may benefit from a large pool of data, specially for iconic, well known conspicuous species. Care must be taken when analyzing data for species that are not easy to identify, as studies have shown that misidentification is not uncommon amongst these platforms.In the United Kingdom, "The Road Lab" was started by Cardiff University in 2012, with the aim of estimating the impact of roads and motoring on British wildlife. Since then it has gathered data on its website, and on several social media platforms including Facebook and Twitter.
In India, the project "Provide Animals Safe Transit on Highways" was initiated by the Environment Conservation Group in 2015, to study the impact of roads on Indian wildlife. A team of five wildlife conservationists led by R. Mohammed Saleem had undertaken a forty-four-day expedition, traveling more than 17,000 kilometers across 22 states to study and spread awareness on roadkill. It is also gathering data on its website, and social media platforms. More focused scientific studies on impacts of traffic on animals have been conducted across India especially in the Western Ghats of south India documenting a large number of species of insects, other arthropods, amphibians, reptiles, birds and mammals killed. Another study conducted on 420 km of roads located along cultivated fields in Punjab showed granivorous birds to be killed far more than their availability, likely attracted to spilled grain on the roads.
In the Czech Republic, an online animal-vehicle crash reporting system Srazenazver.cz is gathering both professional and volunteered data on roadkill and wildlife-vehicle crashes. The application allows users to input, edit and browse data. The data is visualized in the form of maps, graphs or tables and analyzed online.
In Australia, wombat roadkill data is collected by the citizen science project, WomSAT.