Wildlife-vehicle collisions are a widespread public safety concern.
Concerns primarily focus on large mammals because their size is more likely to result in human casualty and motor vehicle damage. Thus, much of the information on wildlife-vehicle collisions is focussed on ungulates and other large mammals (Putmam, 1997; Clevenger & Waltho, 2000; Gloyne & Clevenger, 2001; Cain et al., 2003; McCollister & van Manen, 2010; Lewis et al., 2011).
Information on small– medium-sized mammals is sparse, making it difficult to determine the extent to which roads affect these species. Despite the fact smaller mammals pose little threat to motorists should they collide with a vehicle, these species still pose a threat to motorist safety (Bjorn et al., 2003). Often motorists act to avoid colliding with animals, thus, motorist behaviour becomes an un- or under variable in road safety reports. Motorists may swerve, reduce speed or stop suddenly to avoid colliding with animals, which could lead to a single vehicle accident or collision with other vehicles (Bjorn et al., 2003).
Canada has seen an increase in wildlife-vehicle collisions over the last several decades with notable cases in all provinces, including Nova Scotia (Table 1 & 2) (Forman et al., 2003; L-P Tardif & Associates Inc., 2003; Government of Canada, 2012; National Post, 2015). Information has not been updated since 2003, thus the current status of collisions is unknown (Government of Canada, 2012). Within Canada there is no primary center that compiles animal-vehicle collisions, and thus data sources are disassociated. Information that is readily available, though outdated, indicates discrepancies in the data. For example, in 2002 Nova Scotia reported one fatality with a large animal, but Transport Canada reported no fatalities that year (Government of Canada, 2012). Specific details are also lacking in reports, such as animal sex or age, exact collision location, etc., thus creating problems with efficient mitigation and identification of areas with higher collision rates. Notably, provincial and federal incidents are underreported; Transport Canada estimates an underreporting of large animal collisions by 50% (Government of Canada, 2012).
Nova Scotia Department of Natural Resources (DNR) records reported White-tailed Deer, Moose, and Black Bear collisions, the province’s primary large mammals. DNR does not record collisions with small–medium sized mammals; nor do equivalent departments in other Canadian provinces. Globally there is a lack of information for collisions of small–medium sized wildlife, unless it is a species-at-risk (L-P Tardif & Associates Inc., 2003; Government of Canada, 2012).
Reducing Wildlife-Vehicle Interactions
Reducing interactions between wildlife and transportation infrastructure is one aim of road ecology (Bjorn et al., 2003; Forman et al., 2003; Vanlaar et al., 2012). Reducing the negative effects of transportation infrastructure on animals is crucial for conservation efforts and improves road safety for both animals and the public. There is no one perfect solution. Current mitigation methods simply seek to reduce negative effects because it is not viable to eliminate them. The type of mitigation method is dependent upon target species and the area where which the species resides. Primarily the objective is to reduce barrier effects by providing alternate means to cross roads, reducing wildlife-vehicle interactions, and thus reducing the risk of both wildlife and human casualties (Bjorn et al., 2003; Forman et al., 2003; Vanlaar et al., 2012).
The most common and least expensive techniques target motorist behaviour and/or alertness (Vanlaar et al., 2012). Warning signs are posted along highways as both permanent and seasonal fixtures and artificial lighting is installed to aid motorist awareness (Huijser & McGowen, 2003; Litvaitis & Tash, 2008; Vanlaar et al., 2012). Sloping and mowing highway verges has also seen positive correlations in reducing wildlife crossings; verges that are level to the road tend to have more crossings whereas verges that are sloped tend to have fewer (Alexander & Waters, 2000; Bjorn et al., 2003; Gunson et al., 2011). Less common and more expensive options are to provide passageways to give animals a means to cross from one habitat to another without physically crossing roads. Wildlife overpasses and underpasses of various designs are used to enable wildlife road crossings and simultaneously reduce wildlife-vehicle collisions, with the added benefit of reducing habitat fragmentation. Because wildlife underpasses and fencing are costly, installation locations are carefully selected in areas that would maximize animal use (e.g. natural movement corridors) (Clevenger & Waltho, 2000; Bjorn et al., 2003; Forman et al., 2003). No combination of these methods can eliminate the negative effects of roads with respect to wildlife-vehicle interactions, but mitigation is increased when multiple methods are used (Bjorn et al., 2003).
Warning systems are designed to modify motorist behaviour, making motorists more aware of animal activities in the area (Huijser & McGowen, 2003; Seiler & Helldin, 2006). Most commonly used warning systems are basic signs warning of a higher frequency of animal crossings in the local area. More advanced systems integrate flashing lights sometimes triggered by infrared sensors that detect mammals approaching the road surface (Bjorn et al., 2003). Often, warning systems are overlooked by motorists because they are permanent fixtures to which humans eventually habituate. Warning signs with lights are shown to be slightly better at catching motorists’ attention, but this system only mitigates motorist awareness; wildlife still cross roads and a high risk for collision remains (Huijser & McGowen, 2003; Seiler & Helldin, 2006).
Wildlife Crossing Structures
Wildlife crossing structures reduce wildlife-vehicle collisions in localized areas (Forman et al., 2003). Wildlife crossing structures facilitate wildlife movement across roads and provide links to fragmented habitats. Overpasses and underpasses are the two primary forms of wildlife crossing structures and each vary in design. Wildlife which travel via the tree canopy would benefit from ‘treetop overpasses’ that connect the tree canopies on opposite sides of roadways with ropes or cables (Bjorn et al., 2003; Forman et al., 2003; Goosem et al., 2005). Wildlife crossing structures are primarily designed with a target species or habitat in mind to optimize animal usage (Forman et al., 2003).
Overpasses provide a continuation of natural landscape for wildlife to cross over top of highways without the risk of casualties (Forman et al., 2003). Other than treetop overpasses, typical overpasses for animals that move along the ground are built to pass large mammals, but the addition of woody cover provides cover for smaller mammals and other taxa as well. Extensive research has been conducted into the success of wildlife crossings using overpasses producing guidelines for optimal designs based on the road-habitat area and target species (Bjorn et al., 2003; Forman et al., 2003); typically designs are for mammals. Large mammals require wider overpasses with the standard width of an overpass being 40– 50 m (Bjorn et al., 2003). Overpasses under 20 m are not likely to accommodate large mammals successfully but will facilitate smaller mammal movement (Bjorn et al., 2003). Smaller mammals can require specially designed enrichment features such as specific vegetation cover, deadfall, and rocky outcrops.
Vegetation is often used as a buffer between the wildlife crossing area and the barricades to traffic below. Shrubbery can cover fences or noise guards that are installed along the edge of the overpass to prevent wildlife from falling off the edge.
Overpasses with concrete substrate show decreased use because the substrate is uncomfortable for wildlife footing; therefore ground cover is added (Bjorn et al., 2003; Forman et al., 2003). Additionally, plants are added; however only plant species with shallow roots can be used because the structural integrity of the overpass can be compromised should deep routes penetrate the structure (Bjorn et al., 2003).
Canada has only eight overpasses, one in Ontario, six in Alberta, and one in British Columbia (CBC News, 2012; Parks Canada, 2014). These overpasses were designed to facilitate large mammal movement in response to growing concerns for motorist and wildlife safety grew. Banff, Alberta is the leader in wildlife crossing structures in Canada and extensive research has been done on its overpasses and underpasses (Sabean, 1989; Clevenger & Waltho, 2000; Gloyne & Clevenger, 2001; Clevenger et al., 2003; Clevenger & Waltho, 2005; Parks Canada, 2014).
Underpasses are economically more feasible than overpasses, and have highly variable designs (Bjorn et al., 2003). Underpasses range from pipe culverts, which can be less than one meter in width, to viaducts that are similar to arched bridges, which can span hundreds of meters over valleys (Bjorn et al., 2003). The openness of an underpass is a major factor driving species use. Underpasses with more openness (i.e. viaducts) attract larger ungulate species, which are inherently weary of confined spaces. The longer the underpass the higher and wider the wildlife crossing structure should be to maintain a high degree of openness (Bjorn et al., 2003). Underpasses that provide ground cover such as dead fall or rocks attract the use of smaller mammals, which are deterred by open spaces (Bjorn et al., 2003; Forman et al., 2003; Beckmann et al., 2010).
Low light availability in underpasses inhibits vegetation growth, which generally makes the environment less suitable for wildlife (Bjorn et al., 2003). A select few underpasses feature atria located in the median of divided highways (Jackson, 1999). Atria allow more light to penetrate wildlife underpasses creating a more suitable habitat for ungulates. Little research has been conducted on the overall effect of atria and it is unknown how they affect most species (Jackson, 1999; Gagnon et al., 2005).
The number of non-wildlife underpasses to facilitate human movement below highways far outnumber wildlife underpasses (Rodriguez et al., 1996; Brudin III, 2003; Ng et al., 2004). Humans primarily use these non-wildlife underpasses for All-Terrain Vehicles (ATVs) and they are not designed with suitable habitat for wildlife crossings. These passageways often have concrete or gravel substrates with no natural material ground cover or features to entice animal use. Underpasses, regardless if they are intended for wildlife or human use, see a decrease in wildlife use if humans frequent them (Rodriguez et al., 1996). Despite these deterrents, wildlife still use human purposed underpasses to cross roads (Rodriguez et al., 1996; Brudin III, 2003; Ng et al., 2004).
Nova Scotia Wildlife-Vehicle Interactions
Nova Scotia is the second smallest province in Canada based on land mass, and is located on the Eastern Seaboard with a population of 949,500 people (Statistics Canada, 2016). Primary transportation routes for the province’s citizens are the 100-series highways, which were primarily single lane until the last couple of decades. After concerns were raised regarding the level of safety associated with single lane highways, many 100-series highways were ‘twinned’ to improve safety (Jacques Whitford Environment Limited, 2005; Doucette, 2016). Expansion of the 100-series highways could increase road kill rates for reasons above and potentially affect local populations of wildlife.
Wildlife Road Mortality in Nova Scotia
Fudge et al. (2007) conducted road kill studies comparing mortality rates of a section of 100-series highways to those of secondary roads (trunk highways and urban streets) from Shubenacadie to Halifax. In Nova Scotia, highest wildlife mortality rates occur between June and August and lowest rates occur between November and February (Fudge et al., 2007). This pattern is likely due to seasonal wildlife activity patterns, because mammals native to Nova Scotia become less active or undergo torpor or hibernation during the winter months (Fudge et al., 2007). White-tailed Deer, Odocoileus virginianus (Zimmermann, 1780), American Black Bear, Ursus americanus (Pallas, 1780), and Moose, Alces alces (Linnaeus, 1758), are often of greater public concern regarding collisions because these are large mammals with the highest risk of causing human mortality.
Mainland Moose are endangered in Nova Scotia, making them a conservation concern, but White-tailed Deer and Black Bear are common throughout the province (Snaith & Beazley, 2004; Fudge et al., 2007). Collision rates are lower with bears then deer, likely because bears are wary of human activities, more so than deer (Fudge et al., 2007). The province reports an annual average of 2,079 deer highway mortalities, 14 moose, and 33 bear between 1999–2003 (Fudge et al., 2007).
However, the most frequently recorded wildlife mortalities in Nova Scotia are those of medium-sized mammals. Medium-sized mammals, such as Raccoons, Procyon lotor (Linnaeus, 1758), Porcupines, Erethizon dorsatum (Linnaeus, 1758), and Striped Skunks, Mephitis mephitis (Schreber, 1776), are often habituated to human disturbances and are often found near roads. These mammals have slower gaits and are too large to fit beneath an oncoming vehicle; thus, collisions are frequent. Fudge et al. (2007) noted in their surveys that 28% of observed road mortalities were raccoon, 27% Porcupine, 17% Striped Skunk, 6% Snowshoe Hare, Lepus americanus Erxleben, 1777, 4% Eastern Coyote, Canis latrans, Say, 1823, and 3% Groundhog, Marmota monax (Linnaeus, 1758). Records of collisions with small mammals or other taxa such as amphibians and reptiles are scarce, as these species are difficult to detect during road surveys and are likely quickly scavenged. Fudge et al. (2007) showed the 100-series highways have a higher mortality rate per km than secondary roads. However, standardizing mortality rates by traffic density between 100-series highways and secondary roads results in similar rates (Fudge et al., 2007).
Surrounding landscapes around roads likely affect mortality rates within the province. Fudge et al. (2007) showed mortality rates were higher for species overall if roads were surrounded by mature forests and roadside topography was level to roads. Road proximity to water did not appear to have a significant effect on mortality rates. It was suggested that roads with greater widths and higher traffic density discourage animals from crossing, thus reducing mortality rates, although roads which have grassy medians could potentially offer a stop over for crossing animals, thereby exacting a similar reduction in mortality rates (Fudge et al., 2007). Overall, mortality rates vary among species and local areas; therefore, many factors must be considered in reducing collisions.