Spatial and Temporal Variability of Herpetofauna Road Mortality and Carcass Persistence within a World Biosphere Region

Abstract

Roads are one of the biggest threats to herpetofauna globally, especially in Ontario as the road network continues to expand beyond urban boundaries, and the human population is projected to add 4 million new residents by 2050. The Long Point Biosphere Region (LPBR) is home to over 50% of Ontario’s at-risk species but contains little remaining in-tact habitat, as past-century land use conversion has resulted in agriculture accounting for over 75% of the land by area. To better understand the spatial and temporal herpetofauna road mortality dynamics within an agriculturally-dominated UNESCO world biosphere, we completed 1,961 systematic walking surveys across 15 road transects between April and October in 2024 and 2025, and again in March 2026. Our research objective was to identify the drivers of temporal trends in road abundance, and assess the influence of environmental factors on road presence, absence, and abundance (Chapter 2). We expected each class to be most frequently on the road at a specific time of the year that corresponds to their annual life history pattern, and nearby landscape features to be associated with habitat use requirements. We encountered 1,606 individuals across the LPBR and found that turtles and snakes were predominantly found at wetland transects in May and snakes again at all transects in September. Anurans were observed on the road at non-agriculture transects in March and September, and salamanders at forest transects in September. Turtle and snake abundance were largely influenced by proportion of aquatic habitat (i.e., wetland and open water) surrounding the road, whereas anurans were most abundant near streams. Salamanders were mainly found at transects with high forest proportion, and were dominated by red-spotted newt migrations in both 2024 and 2025. Our findings highlight class-specific patterns that can be used to target mitigation efforts within the LPBR including exclusion fencing, wingwalls, culverts, and road closures. However, road mortality studies are known to severely underestimate the true number of collisions due to removal from the road by mechanical means or scavenger behaviour, with many studies reporting over 50% carcass removal in less than 24 hours. To quantify this magnitude for our study, we monitored 111 herpetofauna carcasses between May and September in 2025 to understand key drivers of carcass road persistence, predict the number of individuals that were missed with our survey effort, and identify how varying levels of survey effort would influence detectability (Chapter 3). We found that there was a significant difference in persistence time among species classes, with two thirds of reptiles removed from the road within 48 hours. Traffic volume was the most important environmental influence on persistence time across all classes. We recommend daily road surveys for reptiles and amphibians to reduce the underestimation of carcasses, as well as implementing more frequent surveys or continuous monitoring methods at known hotspots where possible. Future road mortality studies should apply correction factors to better represent the true mortality within their target population.