Road Mortality Mitigation

 

Beaver Ponds; K. Ovaska Photo

Fencing & Passages

 

Turtles can be exposed to road kill during migrations to and from wetlands and nesting areas on land or when moving among wetlands. Mortality of adult females, in particular, can be devastating to turtle populations that rely on high adult survival for their persistence (add ref). Situations where a nesting area is located across a busy road from water bodies are particularly hazardous. Several technics exist to mitigate road mortality of turtles. Underpasses with drift fences that direct turtles to the passages are suitable for identified migration corridors and well-defined problem areas. In some cases, permanent fencing along the road together with enhancing or creating a nesting area on the wetland side are appropriate. The problem with this method is that turtles can be persistent in attempting to reach tradional nesting areas, and fences have to be long and completely turtle-proof.

Turtles are wary of passages that are dark and of small diameter. These problems can be overcome by using large-diameter culverts or other structures and adding light for longer tunnels. Turtles are known to use square culverts with dimensions of 180 by 180 cm (6x 6 feet) as passageways to cross roads[1]. CARCNET website (http://www.carcnet.ca/english/tunnels/spotted_turtle_tunnel.php) describes a case where a tunnel equiped with a grate to let in light was used to create a safe passage for the Spotted Turtle. Similar specialized underpasses have been used with success for amphibians, and many designs are available (see http://www.carcnet.ca/english/tunnels/amph_tunnels.php). Any installed structures need to be monitored for their effectiveness for turtles. See http://www.icoet.net/ICOET_2011/documents/posters/CRB-P71-DYorks-Poster-ICOET2011.pdf for experiments testing various tunnel designs for freshwater turtles.

Signage

 

Interpretive signs placed in strategic locations in turtle habitat function to increase the public' awareness of turtles and threats to populations and habitat. These signs are particularly useful in parks, beaches, and other recreational sites where turtles occupy wetlands or nest on swimming beaches, in camp sites, or in picnic areas.

Road signs that alert drivers to the possible presence of turtles on the road can be useful for preventing road mortality, although their effectiveness is largely untested. Signs are expected to function best on small side roads - other measures, such as fencing and underpasses, are more appropriate for busy roads and highways. Turtles are especially vulnerable to road mortality where roads intercept migration routes between water bodies and nesting areas on land. Although signage may reduce road kill of adults, it is probably ineffective in preventing mortality of hatchlings, which are too small for most drivers to detect. Again, consider other other methods to prevent hatchling road mortality. See additional pages for examples for case studies of road signage.

Other Techniques

Trapping and manually moving turtles across roads is a temporary method that can be deployed to alleviate road kill in problem areas. This method is labour-intensive and suitable as an emergency measure until more permanent measures, such as underpasses, can be put in place. It is also suitable for hatchling turtles in areas where turtles nest on gravel road sides and where nest sites have been identified.

- To keep turtles off the road, install low (about 2' high) drift fencing flush to the ground on the side of the road; either visually monitor the fence or add a turtle trap (to be described) at each end and at periodic intervals; monitor the fence frequently and move turtles across the road by hand as they are found.

- If the locations of road side nests are known (e.g., emerging nests have been identified by developing exit holes), place a box frame (about 2' x 2') with hardware cloth top on the nest; be sure to insert a branch or an equivalent object to provide shade for the emerging hatchlings. Inspect the boxes frequently and transport emerged hatchlings across the road to the nearest suitable water body.Be patient and let the hatchling turtles to dig their own way out.

Case Study 1: Mitigating Road Mortality of the Western Painted Turtle in the Municipality of Saanich: Road Sign Installation in 2010.

Prepared by Christian Engelstoft1, MSc, RPBio, Kristiina Ovaska1, MSc, PhD, Adam Taylor1, and Darren Copley2

1Habitat Acquisition Trust, P.O. Box 8552, Victoria, BC, V8W 3S2
2District of Saanich, 770 Vernon Avenue Victoria BC V8X 2W7

This project is part of broader conservation effort aiming to mitigate threats to endangered Pacific Coast populations of Western Painted Turtle (Chrysemys picta bellii) on Vancouver Island. In an attempt to mitigate road mortality, the District of Saanich in collaboration with Habitat Acquisition Trust, erected two “turtle crossing” signs in an area where mortality had been observed in 2008 and 2009 on Beaver Lake Road. Signs were installed in late March and removed in mid-September 2010. One of the signs had to be replaced because it disappeared soon after its installation. The road and road shoulders between the signs were surveyed for turtles 117 times from March to July 2010, when hatchlings emerge from their nests and females lay their eggs. Over a weekend, a traffic counter was installed for a 5-day period both before and after the signs were erected. In the first period, 1584 vehicles passed the site going an average speed of 34 km/h; the speed of 85% of the vehicles was less than 42 km/h. In the second period, 2089 vehicles passed the site going an average speed of 33 km/h; the speed of 85% of the vehicles was less than 40 km/h. More than 69-75% of the traffic occurred between 10:00 to 16:00.

The slightly lower speed after the installation of the signs did not prevent five Western Painted Turtle hatchlings from being run over on 31 March 2010. A desiccated Western Painted Turtle hatchling was found on the side of the road on 26 April. A newly emerged nest on the shoulder of the road adjacent to the road kill site was located on 31 March, and we assumed that all six hatchlings emerged from this nest as it was the only nest found in the area. No adult females were seen laying eggs and no other signs of nesting were observed along the road. We did observe adult turtles crossing adjacent gravel roads in June and July 2010.


Considering the small size of newly hatched Western Painted Turtles, it is not surprising that motorists did not see the juveniles on the road. A more effective measure for protecting hatchling turtles would be to install a low fence around the nest sites. The enclosure should be monitored daily for hatchlings and, if found, they should be carried to the nearest pond.

The intention of the signs was to prevent adult mortality, and we documented that the majority of the traffic occur during the day time. Generally the Western Painted Turtle females lay their eggs at dusk and dawn, so traffic at this time of day is the greatest threat to them. Drivers that regularly pass the signs would have been alerted to the possibility of encountering turtles on the road and hopefully would have been prepared to avoid a collision. The signs also functioned as outreach tools, informing drivers of the presence of turtles in the area and their vulnerability to road mortality.

We recommend that the signs be reinstalled for the March – July hatching and breeding period in 2011, that motorist be surveyed to find out whether they saw the signs and how it affected their behaviour. We also recommend that the road be monitored for mortality, turtle nests, and that, if emerging nests are found, the nests be protected with an enclosure and hatchlings be carried to the nearby pond.

  1. Kaye DR, Walsh KM, Rulison EL and Ross CC. 2006. Spotted turtle use of a culvert under relocated Route 44 in Carver, Massachusetts. IN: Proceedings of the 2005 International Conference on Ecology and Transportation, Eds. Irwin CL, Garrett P, McDermott KP. Center for Transportation and the Environment, North Carolina State University, Raleigh, NC: pp. 426-432.

 

Western Painted Turtle Conservation