Culvert use by Chelydra serpentina to move
between wetlands bisected by a highway
Briita Orwick1 and Dr. Tom Langen2**
Introduction
Wetlands with high road densities and traffic flows show significant declines in
herpetofauna species richness and abundance (Findlay et al. 1997, 2001; Houlahan and Findlay
2003). Each year along Hwy. 68 in St. Lawrence County, New York thousands of frogs and over
a hundred turtles are killed due to vehicle collision (Langen unpublished data).
Turtles, with their late reproductive maturation and long life-span are especially
susceptible to population decline due to changes in their environment that lead to high adult
mortality rates (Gibbs and Shriver 2002). Roads present a real threat to turtle survivorship as they
move from one habitat to another. Turtles will migrate considerable distances to forage, nest,
pursue potential mates, and disperse as juveniles.
Our study is conducted within the Upper and Lower Lakes Wildlife Management Area
(3,554 ha), with marsh and shrub swamp being a predominant feature (75˚ 15’ N, 44˚ 40’ W).
The area is bisected by NYS Highway 68. These stretches of pavement increase habitat
fragmentation and pose a threat to the herpetofauna that try to cross over them. Over time turtle
populations can experience reduced fecundity and increased mortality in isolated patches of
habitat, resulting in turtle populations that are unable to sustain themselves (Klemens 2000).
In an attempt to mitigate large reptile and amphibian mortality along Hwy. 68, roadside
barriers were installed in April 2006 by the New York State Department of Transportation.
228.44 meters of wood and wire fencing separate deep marsh from the highway on the east side,
while on the west 244.66 meters of exclusively wire fencing separate the highway from shrub
swamp and open impounded water (Langen unpublished data). The roadside barriers are located
along a 385 meter transect that bisects adjacent wetland, therefore representing a causeway zone
with abundant amphibian and reptile populations and subsequently much road crossing. As the
barrier clearly represents an obstacle for animal movement, alternative routes must be present. A
1
Class of 2007, Department of Environmental Studies, Lewis and Clark College, Portland, OR 97219,
participant in NSF-REU Program in Environmental Science and Engineering, Clarkson
University, Summer 2006, oral presentation
2
Project Mentor and Associate Professor, Department of Biology, Clarkson University, Potsdam, NY
13699
steel culvert measuring 1.22 meters in diameter passes under the road and remains half full with
water in summer months. The culvert allows for water levels to equilibrate, but also acts as a
possible vector for animal movement.
The goal of this project is to analyze the success of the culvert located within the test site
as a passageway to maintain turtle population connectivity. Turtles were captured at the test site
and surrounding areas and later released with radios attached to their carapace. I predict that a
portion of the turtles observed will use the culvert system to return to their capture site. By
tracking turtle movements within a roadside barrier culvert system we can better forecast the
outcome of future implemented systems of this design in regards to turtle migratory movements.
Methods
To determine whether turtles moved freely through the culvert system WL300-7PN slow
pulse radios each weighing 14 grams were attached to the carapaces of nine snapping turtles
using epoxy glue. One painted turtle was equipped with a similar radio that weighed six grams to
compensate for its smaller body mass. Turtles were hand-captured or caught while nesting
alongside the road. Hoop-net traps and floating traps that target basking turtles were also used to
capture turtles that were later fitted with radios in lab. Turtles were released on the opposite side
of the highway from their capture site under the hypothesis that they would attempt to return to
their original range. Radio-tracking started June 6, 2006 and is continuing. On average, every
three days during this period the location of each turtle has been determined using an AVM
Instrument LA 12-Q Radio-telemetry receiver and hand-held antennae. The precise coordinates
were measured using a handheld Garmin GPS device. After sufficient data has been recorded for
the movements of each radioed turtle I will map their routes using ARC GIS 8.1 geographic
information systems (GIS) software. With these maps we will be able to compare movement
patterns among the ten radioed turtles, and interpret whether culverts are sufficient for
maintaining turtle population connectivity.
Results
As of July 19, 2006 two radioed snapping turtles have successfully used the culvert to
cross from one side of Hwy. 68 to the other. One such turtle crossed through the culvert from the
east side of Hwy. 68 just three days after it was released, and traveled a great distance past its
original capture site on the western side of the highway. The second turtle passed under the road
through the culvert system and was caught in a hoop trap on the other side just seven days after it
was released.
References
Findlay, C.S., and J. Houlahan. 1997. Anthropogenic correlates of species richness in
southeastern Ontario wetlands. Conservation Biology 11:1000-1009.
Gibbs, J.P., and G. Shriver. 2002. Estimating the effects of road mortality on turtle populations.
Conservation Biology 16:1647-1652.
Langen et al. 2006. Methodologies for surveying patterns of herpetofauna road mortality along a
highway network. Journal of Wildlife Management. In press.
Mitchell, J.C., and M.W. Klemens. 2000. Primary and secondary effects of habitat alteration.
Pages 5-21 in M.W. Klemens, editor. Turtle conservation. Smithsonian Institution Press,
Washington D.C.