Surveying and Predicting Hotspots of Herpetofauna
Mortality on New York State Highways
Lindsay Schwarting
Biology / Environmental Science & Policy
Introduction
Our steadily rising human population has had far reaching effects on the natural landscape and
the species that inhabit it. As a result of this growing human population, roads are becoming an
increasingly prevalent feature of landscapes. Roadways have seven general negative effects on both
aquatic and terrestrial ecosystems. These include, but are not limited to, mortality from road construction,
mortality from vehicular collision, the modification of animal behavior, the alteration of the physical
environment, the alteration of the chemical environment, the spread of exotics, and the increased use of
areas by humans (Frissell and Trombulak, 1999).
Herpetofauna populations (reptiles and amphibians) are especially susceptible to the effects of
roadways because of their demographic sensitivity. Turtles in particular are typified by their low annual
birth survival rates and delayed sexual maturity. Consequently, turtle populations have a difficult time
recovering from the loss of individuals; even the smallest change in population size could have a drastic
impact on the population of the species as a whole.
Herpetofauna populations are also highly vulnerable to the effects of human roadways because a
major portion of their life histories include migration between wetland habitats and breeding in upland
areas. Females prefer to nest along roadways. The sandy shoulders and elevated temperatures are ideal
for nesting.
Roadways have the potential to be demographic barriers between wetland habitats, and slowmoving herpetofauna cannot consistently handle these barriers successfully. Roads built through or near
wetlands typically cause higher mortality among reptiles and amphibians, and create barriers to dispersal
(Aresco, 2005). These particular segments of roadway show a higher herpetofauna mortality rate than
others.
Beginning in 2002, surveys of 145 points distributed throughout 353km of highway in St.
Lawrence County, New York were conducted for road mortality of amphibians and reptiles. Survey data
was analyzed based upon natural habitat composition and road structure, in order to identify features that
best predict ‘hotspots’ of mortality. In 2004, surveys were repeated at a subset of 40 locations to quantify
repeatability (Langen in press). Again, these 40 locations were surveyed in 2006. It was found that
Clarkson University, Class of 2008
Biology / Environmental Science & Policy
Honors Program
Mentor: Dr Tom Langen
Poster Presentation
hotspots of herpetofauna mortality were located along heavily traveled highways surrounded by wetland
and forest landscape. However the best indicator of mortality hotspots was the presence of causeways, a
landscape configuration that consist of wetlands on both sides of the road within 100m of the pavement.
The specific objective of our research is to validate whether or not causeways can predict
hotspots of mortality located along highways throughout areas of New York State.
Methods
To accurately locate potential hotspot areas, ARCView GIS (Geographic Information Systems)
software (ESRI) was utilized to pinpoint causeway areas in multiple regions of Northern New York State.
Land use data utilized in this software was obtained from the New York State Department of
Environmental Conservation Regulatory Wetland Maps and road maps were obtained from the Cornell
University Geospatial Data Information Repository (CUGIR). The software was also used to choose
random points along the roadways for comparison against the causeway points.
The regions surveyed included the St. Lawrence Valley, the Adirondack State Park, the
Champlain Valley, and the Lake Ontario Lowlands. Due to relative size differences in the regions, 80
coordinate GPS points (40 causeway and 40 random) were surveyed in both the St. Lawrence Valley and
Adirondack State Park, while only 40 coordinate points (20 causeway and 20 random) were surveyed in
the Champlain Valley and Lake Ontario Lowlands. Causeway and random coordinate points were
located using the Garmin GPS 12XL global positioning device. From the center of each GPS survey
point, a 50m transect was measured and walked in either direction along the road. Any reptiles or
amphibians found in this 100m stretch of road were classified and recorded. Also noted, were any
significant physical features about the landscape (presence of water, sand, etcetera) that would influence
the size and type of reptile and amphibian populations found in the region.
From what is known about the habitat preferences of herpetofauna, we predicted that causeway
areas would produce a higher mortality among reptiles and amphibians than randomly chosen areas. The
need to migrate between wetland areas puts reptiles and amphibians at an elevated risk of mortality at
these areas.
Results & Discussion
Initial examination of the data indicates causeways produce a much higher rate of herpetofauna
mortality than random points along the road. The presence of wetlands within 100m of both sides of a
heavily traveled road greatly increases the probability of mortality among these species.
Clarkson University, Class of 2008
Biology / Environmental Science & Policy
Honors Program
Mentor: Dr Tom Langen
Poster Presentation
Our results indicate that it is possible to form predictive models of hotspots of herpetofauna
mortality. Road characteristics, wetland configuration, and land use data greatly aid in the development
of these models. Land and resource managers will be able to use these models to effectively plan new
roads and mitigate existing roads by placing highway barriers that minimize reptile and amphibian
mortality.
Works Cited
Aresco, Matthew. 2005. Mitigation Measures to Reduce Highway Mortality of Turtles and Other
Herpetofauna at a North Florida Lake. Journal of Wildlife Management 69: 540- 551
Frissell, Christopher and Trombulak, Stephen. 1999. Review of Ecological Effects of Roads on
Terrestrial and Aquatic Communities. Conservation Biology 14: 18-30.
Langen, Tom, et al. Locating Hotspots of Road Mortality. Journal of Wildlife Management. In press.
Clarkson University, Class of 2008
Biology / Environmental Science & Policy
Honors Program
Mentor: Dr Tom Langen
Poster Presentation