Where did the tortoise crossed the road? Predicting road mortality hotspots for Hermann’s tortoise in Romania

The Eastern Hermann’s tortoise has its core Romanian range in southwestern part of the country, in the Iron Gates area, close to the border with Serbia. During the socialist era, development has less impact on the region, due to a combination of geopolitical and environmental factors: a mountainous area, proximity to the Danube, and a strictly militarized border with the former Yugoslavia. However, post-socialism has brought significant changes: hundreds of lodges and vacation homes, road traffic increases, and the Iron Gates area is projected to become one of the most important tourist attraction in SW Romania. The tortoises would be affected by these changes, and to provide an input for conservation authorities, we implemented a broad-scale study aiming at modeling road-mortality hotspots of Eastern Hermann’s tortoise in its Romanian range.

Eastern Hermann’s tortoise (photo by the authors of the paper)

First, we ran a velocity experiment, in order to estimate the average speed of tortoises on paved surfaces. As expected, the tortoise are slow (average speed = 3 meters/minute), males moved slightly faster than females, and heavier tortoises proved to be the slowest.  Second, we used this empirical data to estimate the probability that a tortoise would be killed as it crosses a road for different road traffic intensities and road types. We found that there was <0.001 probability that a tortoise would be killed on unpaved, local roads, and this probability increased up to 0.19 for high traffic, 4-lane roads. The maximum road mortality probability estimated for Hermann’s tortoises in Romania was 0.53 for the European E70 high traffic 4-lane road, which crosses the eastern part of the range (at current traffic levels of 6500 vehicles/day). If the traffic is to increase to 35000 vehicles/days, every tortoise attempting to cross this road would be roadkill. Lastly, we estimated annual road-associated mortality within the entire range using the probability of being killed during a road crossings and the number of the roads an adult tortoise would encounter during its annual movements. We identified local hotspots of mortality significantly higher than expected. Overall, the predicted mean annual road-associated mortality for the entire range was 1.6%, but several population groups bisected by European or National roads may lose up to 30% of the population any given year.  While the overall mortality sees low, it could be a tipping point for population declines (if it has not yet happened) given the synergy with other threats, such as poaching, nest predation, afforestation of abandoned hayfields, and increase in fire frequency.

Eastern Hermann’s tortoise - roadkill (photo by the authors of the paper)

The main result of our broad-scale modeling approach – the identification of road mortality hotspots – can be used in road mortality mitigation efforts. We identified population groups under no risk of road-associated mortality, mainly due to isolation from the nearest roads or adjacency to low traffic, unpaved roads. For the road mortality hotspots associated with National and European roads, a range of mitigation techniques could be implemented: underpasses, roadside fences, guardrails, signage, as well as drivers education. While some strategies, such as underpasses and roadside fences can be costly, signage and drivers education are critical not only for Hermann’s tortoises, but for other wildlife at risk from road mortality.

Reference 

Modeling road mortality hotspots of Eastern Hermann’s tortoise in Romania, Amphibia-Reptilia, doi: 10.1163/15685381-00002878

Ruben IOSIF^ab, Laurenţiu ROZYLOWICZ^a, Viorel Dan POPESCU^ac

a) Centre for Environmental Research (CCMESI), University of Bucharest, 1 N. Balcescu Blvd., RO-010041, Bucharest, Romania. 

E-mail RI: ios_ruben@yahoo.com, 

E-mail LR: rozylowicz@gmail.com 

b) Faculty of Natural and Agricultural Sciences, Ovidius University of Constanţa, Aleea Universităţii 1, Building B, 900470 Constanţa, Romania

c) Earth2Ocean Research Group Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
E-mail: viorelpopescu@gmail.com