Mitigating wildlife-vehicle collisions in Leeds and ...

Authored by Emma Phillips and Katie Black

You may have noticed that our observation list is dominated by insects lately, with Common Eastern Bumble Bee being our most observed species. You might be asking, “Isn’t this project primarily targeting reptiles?”. While the answer is yes, we've also been recording conspicuous insects that we encounter on roads. We've made some interesting observations related to pollinators and roadside habitats. Throughout the field season, we’ve documented a high abundance of pollinator species both active in roadside vegetation and killed on roads due to vehicle collisions.

Despite evidence of vehicle-induced pollinator mortality, roadsides can provide a variety of benefits to pollinators, and there’s a growing interest in roadside pollinator projects (e.g., Lanark County, 2021). Our natural landscapes have changed significantly due to human development, and roadside vegetation offers a food source through the nectar and pollen of wildflowers, important reproductive host plants for butterfly and moth species, and breeding, nesting, and overwintering habitat (Hopwood, 2013). Roadside habitats can also help pollinators move through landscapes by linking fragmented habitats (Hopwood et al., 2015). Unfortunately, not all roadsides benefit pollinators (Hopwood, 2013). Roadsides managed with high-frequency mowing, broadcast spraying of herbicides, and planted with non-native grasses support a much lower diversity of pollinators and directly cause population decline (Hopwood, 2023). Our observations reflect such effects, with higher pollinator observations at sites dominated by native vegetation. These roadside vegetation management practices are used to achieve three main goals: decrease the risk of wildlife-vehicle collisions, prevent the spread of invasive and noxious weeds, and prevent erosion (Hopwood et al., 2015). So, how do we change our current efforts to focus on pollinator conservation while still achieving our goals and remaining cost-efficient?

The first step is re-establishing and promoting native vegetation (Storey et al., 2020). Roadsides with a high diversity of native vegetation have been found to support 35% more bee species by providing optimal foraging and nesting habitat for pollinators throughout the growing season (Hopwood, 2003). Once established, a high diversity of native vegetation also helps prevent erosion, reduces noxious/invasive plant abundance, reduces stormwater runoff, and causes fewer driver visibility issues (Storey et al., 2020). The second step is to modify the timing and frequency of mowing completed during the growing season (Hopwood, 2013). High-frequency mowing is a common practice, as we have observed at our survey sites, with mowing occurring at least four times already this year. Studies have found that mowing once in the early spring or late autumn, selective mowing of unwanted plant species, or eliminating mowing can increase the diversity of native species while reducing runoff, erosion, and the spread of invasive species (Storey et al., 2020). Lastly, herbicide use can be modified to target and control specific unwanted species in replacement of broadcast spraying (Storey et al., 2020). This method ensures that target species are treated and limits the adverse effects on the surrounding environment (Storey et al., 2020).

Implementing roadside vegetation management practices that benefit pollinators can significantly improve monetary savings for road agencies (Storey et al., 2020). Such savings are derived from decreased human effort, equipment, and other resources, along with increasing the value of ecosystem services associated with pollinator abundance and diversity (Storey et al., 2020). A study completed by the Florida Department of Transportation revealed that a reduced mowing frequency had the potential to save 30% ($1.2 million) of their annual budget, and the ecosystem services provided by sustainable management could be valued at $0.5-1.5 billion annually (Storey et al., 2020). Similarly, the Georgia Department of Transportation implemented reduced mowing due to budgetary constraints, with the cost savings being $10.95 million the following year (Storey et al., 2020). These studies demonstrate the potential economic gain of adopting a pollinator-friendly roadside management plan.

While adopting such an approach seems to bring many benefits, there is a concern that enhancing roadside habitat may increase pollinator mortality due to vehicle collisions. Our observations to date include 538 dead pollinators caused by presumed vehicle collisions, including 266 bees and 49 butterflies. Anecdotally, we seem to be finding more dead pollinators in road areas that have ideal roadside habitat. These observations are concerning, especially since our transects only cover a total of 2.6 km of County roads, and there were likely many individuals missed. However, research shows that roadside vegetation management with pollinators in mind can mitigate road mortality and increase species richness and abundance, and further considerations can be made to minimize collisions (Daniel-Ferreira et al., 2022; Skorka et al., 2013). Overall, increased diversity of native flowering plants is positively correlated to increased pollinator species richness and abundance and a comparatively decreased number of individuals crossing the road (Storey et al., 2013). In other terms, the larger the pollinator population, the lower the impact of road mortality, meaning better-suited roadside habitat will mitigate the potential effects of population decline due to vehicle collisions (Storey et al., 2013).

Restoring and widening road shoulder habitat by even 1 meter can drastically increase the number of pollinators at a site (Skorka et al., 2013). In areas with narrower habitat, there is not enough habitat to support high pollinator populations, causing road mortality to be a more significant risk in overall population decline as individual deaths pose a more significant impact (Skorka et al., 2013). Areas where roadside habitat can be expanded should therefore be a focus for pollinator conservation efforts (Skorka et al., 2013).

In combination with roadside habitat width, traffic intensity and road width influence pollinator roadkill (Daniel-Ferreira et al., 2022; Skorka et al., 2013). For bumble bees, high traffic intensity can double road mortality compared to less travelled roads (Daniel-Ferreira et al., 2022). The rate of butterfly mortality in the same scenario is not as significant, but when combined with a larger road width where butterflies need to travel longer distances, there can be a more substantial increase (Skorka et al., 2013). Due to these factors, it is recommended that conservation efforts for roadside habitat focus on roads with lower traffic volumes, narrower roads, and lower speed limits (Skorka et al., 2013).

Landscape features surrounding the road should also be considered when prioritizing pollinator conservation efforts (Daniel-Ferreira et al., 2022; Skorka et al., 2013). Having native grasslands and meadows in close vicinity to roads is significant, as it provides additional habitat and refuge for pollinators, increasing overall populations both on roadsides and within the broader landscape (Daniel-Ferreira et al., 2022; Skorka et al., 2013). When this habitat is available, populations of pollinators such as butterflies and bumble bees can boom and are more likely to avoid roads (Daniel-Ferreira et al., 2022; Skorka et al., 2013). In contrast, pollinator road mortality can be higher along roads next to forests as wooded areas do not typically provide the type of habitat that pollinators prefer (Daniel-Ferreira et al., 2022; Skorka et al., 2013). In this scenario, pollinators may be more likely to travel via open roadways, increasing risk of vehicle collision (Skorka et al., 2013). Restoration of roadside habitat for pollinators in forested areas may therefore cause more harm than good, so future efforts should focus on roadsides adjacent to grassland and meadow habitat (Skorka et al., 2013).

Human settlements, especially in rural or agricultural areas, have also proved to be beneficial landscape features for successful pollinator roadside habitats (Daniel-Ferreira et al., 2022; Skorka et al., 2013). Farmland and residential areas provide an opportunity for many flowering crops and gardens, which increases pollinator habitat away from roadsides (Skorka et al., 2013). This decreases the need for pollinators to travel across roads when foraging and nesting (Daniel-Ferreira et al., 2022; Skorka et al., 2013).

This is where you can help! When planting new gardens, consider designing spaces that are pollinator-friendly, including a high diversity of native flowering vegetation. For more information, visit this website, and BEE friendly to our important insect friends: https://www.toronto.ca/services-payments/water-environment/live-green-toronto/help-native-bees-pollinators/#:~:text=Provide%20continuous%20bloom%3A%20Pollinators%20need,to%20find%20and%20collect%20pollen.

References

Daniel-Ferreira, J., Berggren, A., Bommarco, R., Wissman, J., Ockinger, E. (2022).
Bumblebee queen mortality song roads increase with traffic. Biological Conservation, 272. https://doi.org/10.1016/j.biocon.2022.109643

Hopwood, J. L. (2013). Roadsides as Habitat for Pollinators: Management to Support Bees
and Butterflies. Proceedings of the 2013 International Conference on Ecology andTransportation. Retrieved from: https://www.researchgate.net/profile/Jennifer-Hopwood/publication/286066214_ROADSIDES_AS_HABITAT_FOR_POLLINATORS_MANAGEMENT_TO_SUPPORT_BEES_AND_BUTTERFLIES/links/5665c80308ae418a786f2b72/ROADSIDES-AS-HABITAT-FOR-POLLINATORS-MANAGEMENT-TO-SUPPORT-BEES-AND-BUTTERFLIES.pdf

Hopwood, J., Black, S. H., Lee-Mader, E., Charlap, A., Preston, R., Mozumder, K., & Fleury,
S. (2015). Literature ReviewL Pollinator Habitat Enhancement and Best Management Practices in Highway Rights-of-Way [PDF]. Federal Highway Administration. Retrieved from https://xerces.org/sites/default/files/2018-05/15-055_01_pollinators_BMPs_in_highway_ROW.pdf

Lanark County. 2021. Media Release: Roadside Pollinator Habitat Restoration Pilot Project Underway. Posted on Monday, May 24, 2021. Retrieved from: https://www.lanarkcounty.ca/en/news/media-release-roadside-pollinator-habitat-restoration-pilot-project-underway.aspx

Skora, P., Lenda, M., Moron, D., Kalarus, K., & Tryjanowski, P. (2013). Factors affecting
road mortality and the suitability of road verges of butterflies. Biological Conservation, 159: 148-157.

Storey, B., Das, S., McFalls, J., Moran, R. A., & Dadashova, B. (2020). Comparison of Cost,
Safety, and Environmental Benefits of Routine Mowing and Managed Succession of Roadside Vegetation. Transportation Research Board of the National Academics of Sciences, Engineering, and Medicine. Printed Document. Retrieved from: https://onlinepubs.trb.org/Onlinepubs/nchrp/docs/NCHRP14-40FinalReport.pdf less ↑