Hot Spots and Hot Times: Wildlife Road Mortality in a Regional Conservation Corridor

Abstract

Strategies to reduce wildlife road mortality have become a significant component of many conservation efforts. However, their success depends on knowledge of the temporal and spatial patterns of mortality. We studied these patterns along the 1000 Islands Parkway in Ontario, Canada, a 37 km road that runs adjacent to the St. Lawrence River and bisects the Algonquin-to-Adirondacks international conservation corridor. Characteristics of all vertebrate road kill were recorded during 209 bicycle surveys conducted from 2008 to 2011. We estimate that over 16,700 vertebrates are killed on the road from April to October each year; most are amphibians, but high numbers of birds, mammals, and reptiles were also found, including six reptiles considered at-risk in Canada. Regression tree analysis was used to assess the importance of seasonality, weather, and traffic on road kill magnitude. All taxa except mammals exhibited distinct temporal peaks corresponding to phases in annual life cycles. Variations in weather and traffic were only important outside these peak times. Getis-Ord analysis was used to identify spatial clusters of mortality. Hot spots were found in all years for all taxa, but locations varied annually. A significant spatial association was found between multiyear hot spots and wetlands. The results underscore the notion that multi-species conservation efforts must account for differences in the seasonality of road mortality among species and that multiple years of data are necessary to identify locations where the greatest conservation good can be achieved. This information can be used to inform mitigation strategies with implications for conservation at regional scales.

Effects of Road Density and Pattern on the Conservation of Species and Biodiversity

“…The reason as to why amphibians in general appear to be more vulnerable to wildlife-vehicle collisions than other taxa has been related to their ecology and life history. Three studies confirmed that road mortality of amphibians peaked as they attempted to cross roads during their migration in the spring from terrestrial hibernacula to aquatic breeding habitats [11,12,14]. These studies recommended that mitigation could be implemented during this seasonal activity period in order to reduce amphibian road-mortality rates; however, a study conducted on Fowler's toad (Anaxyrus fowleri) cautioned that road mortality may not always be limited to seasonal migrations [15].…”

“…For example, of the 27 studies that investigated road-related mortality in up to three related species, 15 studies involved species of conservation concern, while the remaining 12 studies considered the common and widespread species that are often reported in wildlife-vehicle collisions. Amphibians appeared to generate the most concern, with a number of multiple-taxa studies finding that they made up the highest percentage of roadkills (as much as 80% recorded, [9][10][11][12]). Studies warn that with many amphibian populations already declining globally any additional nonnatural mortality could further impact population persistence [13].…”

“…In fact, many of the research studies undertaken on road mortality tended to explore the differences between and within species with the intention of informing more targeted mitigation. For instance, studies considered in this review found that a variety of species-associated factors influenced the rate of wildlife-vehicle collisions, such as age (particularly dispersing juveniles; [19][20][21][22][23]), activity patterns (such as nocturnal and migratory activities; [6,7,24,25]), season (primarily breeding season; [12,[26][27][28][29]), gender (such as males ranging further in the breeding season in search a mate; [23,26,[30][31][32]), diet preferences (e.g., one study found that omnivorous mammals and herbivorous birds were most vulnerable; [33]), mobility (including low-flying species; [15,21,34,35]), behavioral responses (e.g., certain species do not respond to oncoming traffic; [15,36]), and home range size (i.e., the larger the home range the higher the probability of crossing a road; [37]). Another study found that species that were more inconspicuous on the roads were more vulnerable to wildlife-vehicle collisions [38].…”

Methods to Monitor and Mitigate Wildlife Mortality in Railways

“…As recommended for roads, railway surveys should be carried out early in the morning (to reduce scavenging, but see also sources of bias below), preferably by two experienced observers walking at specified railway stretches, one on each side of the rail (Peña and Llama 1997), and covering a 10 m sight strip whenever logistically possible. The use of a vehicle could be a better choice if parallel dirty roads exist (at least on one side), and in cases where the surveyed stretch is too long (>10 km), but their detectability as proved to be lower (Garrah et al 2015). Once a carcass is found, and depending on its state of decay, several variables should be recorded: species, age, sex, GPS location, time of day, weather conditions, position on the railway (verges, between lines, rock ballast, etc.…”

“…The nearest neighbour hierarchical clustering identifies groups of points based on "nearest-neighbor-method" criteria (Gomes et al 2009). Finally, the Getis-Ord Gi* statistic identifies hotspots by adding the number of casualties associated with a given segment of the road to the casualties of its neighboring segments, and compares that value with an overall expected distribution (Garrah et al 2015). Integrating the information on rail sectors with high mortality rates with GIS mapping tools leads to the identification of the locations where mitigation measures (drift fences, rail passages, traffic regulation, etc.)…”