Effects of Roads and Fencing on the Microclimate of
Turtle Nests
*Andrew Davis
Mentor: **Dr. Tom Langen
The microclimate of a turtle nest determines major physiological characteristics of the hatchlings,
including the mass of the eggs during incubation, the mass of the hatchlings, and the sex of the turtle
(Cagle et Al. 1993). The microclimate also affects the duration of incubation. Our study has been
designed to quantify how paved roadways and fencing affect the soil microclimate at locations where
turtles habitually nest.
The sex of a turtle is determined by the temperature of the nest during incubation (Janzen 1994).
This process is called temperature-dependent sex determination (TSD). In turtles, nests that incubate at
higher temperatures tend to produce female hatchlings and lower temperatures result in males. The sex
ratio of a nest can be affected by as little as a 2° C change in temperature (Kolbe 2002). In one study
conducted in Nebraska on snapping turtles (Chelydra serpentine) documented a dramatic difference in the
sex ratio when the temperature of the nest was changed from 25.8° C to 23.9° C (Kolbe 2002). Similar
trends were found in Illinois during a study on painted turtles (Chrysemys picta); a temperature change
from 26.6° C to 24.5° C caused the nest to shift from 0 to 100 percent male hatchlings (Kolbe 2002).
This sensitivity to temperature change indicates that any change on the surface, including roads, fences,
and vegetation, can cause dramatic differences in a nest’s sex ratio.
The humidity of the nest is another environmental influence that can alter the physical traits of the
hatchlings. The shell of a turtle egg is semi-permeable and therefore allows water to move through it.
When the egg is in a more humid environment, it absorbs a large amount of water from the surrounding
soil. However, in a drier nest, the egg will not absorb as much water and may even lose some of its mass.
This means the eggs in the moist nests will be have more mass and will yield larger hatchlings (Packard et
al. 1991), which have a higher probability of living to sexual maturity (Cagle et al. 1993). The eggs from
a more humid nest also have a longer incubation time then the eggs from a drier nest (Packard et al.
1991). The humidity of the nest does not, however, have any influence on the gender distribution of the
hatchlings (Packard et al. 1991).
These two environmental factors have a profound affect on the hatchlings’ lives. Any change in
the surface that also changes the temperature and humidity of the surrounding soil has the potential to
*Clarkson University Honors Program, Class of 2010, Biomolecular Science Major
** Associate Professor of Biology, Clarkson University
dramatically influence reptile eggs incubating in the soil. In our study, temperature and humidity probes
were used to measure how a paved road and two types of fences affected the soil. The paved road used in
the study was a causeway on New York State Highway 68, Upper and Lower Lakes Wildlife
Management Area in St. Lawrence County. The two fence designs were about 0.5 meters high and were
designed as a barrier to keep amphibians and reptiles from the boarding wetlands off the road. The first
fence was wooden. It consisted of three boards nailed horizontally to support posts and had a wire mesh
to cover the cracks between each board. The second fence was a 10 cm by 5 cm gauge wire mesh, with
the smaller wire mesh from the wooden fence bordering the bottom. Each fence was positioned
approximately halfway between the road and the swamp. These three locations where chosen as the focus
of the study because of the turtles’ natural tendency to construct their nests nearby.
To measure the temperature, sensors called “ibuttons” were buried. The ibuttons are programmed
to take a temperature reading every hour. During this study, they were left in the ground for the month of
July, when turtle nests are incubating. In order to make retrieval easier, the ibuttons were encased in a
wire cage and tied to a nail. They were buried about 0.2 meters below the surface of the soil. Five were
buried along both types of fences, three were buried along the roadway across from the metal fence, and
four were buried along the roadway across from the wooden fence. Later in the study an additional seven
ibuttons were buried. With these new ibuttons there were a total of seven along each fence, five along the
road across of the metal fence, and five along the road across from the wooden fence. They were buried
0.2 meters from the road or fence and 1.2 meters apart.
The experiment also required measurement of the soil humidity. To do this, watermark soil
moisture meters were buried. Three were buried along each of the two types of fencing and four were
buried along the roadway, two across from the metal fence and two across from the wooden fence.
Readings were taken throughout the month of July using a voltmeter.
We predicted that the highway pavement will produce the highest temperatures and the most
fluctuation in soil humidity. The high temperatures are a result of the surface material, pavement. The
pavement absorbs the heat from the sun and this energy is transferred into the nearby soil, raising the soil
temperature. The high temperature will result in a large percentage of all-female nests or nests that are
biased toward the female sex (Janzen 1593). Along with the temperature, the surface material will also
cause a large amount of variation in the soil moisture. On hot, sunny days the heat will be amplified by
the pavement. This will cause the soil to desiccate. Conversely, on wet, rainy days the pavement will not
absorb the precipitation and the water will run off onto the shoulder of the road, elevating the soil
moisture. Consequently, the size of the eggs and hatchlings and the length of incubation will be
dependent on the precipitation. We believe that this fluctuation in humidity will adversely affect the
development of the eggs. This is because the eggs rely on passive processes to absorb moisture from the
soil surrounding them. The constant change in the soil humidity will cause an equal amount of variation
in the mass of the egg. The instability of the egg mass could cause the embryo’s mass to change as well.
Constant weight gain and loss may adversely affect the development of the hatchlings. Ultimately, this
could result in small, lethargic hatchlings that have a short incubation time.
We hypothesized that the wooden fence will cause the soil to have the highest humidity and
lowest temperature. The design of the fence creates a large shadow. By blocking the sun, the wooden
fence causes the soil to cool. The lower temperature will produce a larger number of all-male nests and
nests with more male hatchings (Janzen 1593). The wooden fence also absorbs and retains a larger
amount of water. The water in the fence may soak down the fence and into the soil. This will raise the
humidity in the soil. The elevated humidity levels will produce larger hatchlings and a larger percentage
will live to sexual maturity.
The metal fence was thought to produce dry, warm soil. Because the fence provides little or no
shade, the soil’s temperature is determined by the sun and the amount of vegetation in the area. Because
of the lack of shade, the area around the metal fence will yield higher soil temperatures then the wooden
fence. However, the metal fence will have a lower temperature then the roadway because there is no
pavement or other surface material to absorb the sun’s energy. We believe this will result in the most
variation in the gender distribution of the hatchlings. The humidity by the metal fence will be relatively
constant. The soil will naturally retain some water from rainfall but, because there is nothing to
artificially enhance the amount of water retention, the humidity will not be as high as the wooden fence.
Depending on the amount of rainfall, this may result in shorter incubation times and smaller hatchlings.
Works Cited
Cagle, K.D., G.C. Packard, K. Miller, and M.J. Packard. 1993. Effects of the Microclimate in Natural
Nests on Development of Embryonic Painted Turtles, Chrysemys picta. Functional Ecology 7:
653-660.
Janzen, Fredric J. 1994. Vegetational Cover Predicts the Sex Ratio of Hatchling Turtles in Natural Nests.
Ecology 75: 153-1599.
Kolbe, Jason J. and Fredric J. Janzen. 2002. Impact of Nest-Site Selection on Nest Success and Nest
Temperature in Natural and Disturbed Habitats. Ecology 83: 269-281.
Packard, Gary C., Mary J. Packard, and Lynda Benigan. 1991. Sexual Differentiation, Growth, and
Hatchling Success by Embryonic Painted Turtles Incubated in Wet and Dry Environments at
Fluctuating Temperatures. Herpetologica 47 : 125-132.