Habitat Preference of the Spotted Turtle

Habitat Preference of the Spotted Turtle in a Micro-Urban Portion of their Southern Range in Eastern North CarolinaMargaret McGuire

15April 3

Advanced Topics in Biological Research Second Draft

Abstract

The spotted turtle, Clemmys guttata, is a semiaquatic freshwater turtle that is on the IUCN

Red List as an endangered species1. Given the endangered condition of the species, many

researchers have attempted to describe the habitat use and behavior of the species to aid

conservation. With the same goal in mind, my study is intended to contribute information about

the species’ ability to survive in highly fragmented portions of its southern range. I tracked four

adult spotted turtles (two males, two females) over three years on a portion of private property in

Eastern North Carolina. The property contains the primary study area, a 0.09-hectare wetlands. I

analyzed the home range of the telemetered turtles and found that some of the home range sizes

were smaller than ever reported, and that the primary study area has a density of 111 turtles, a

density larger than any reported study. There was evidence that spotted turtles vary their home

range annually, and that there is no specific relationship between sex and home range size. I

studied the growth rates of juveniles captured during the study and found that their growth rates

do not appear to be stunted despite the small area of wetlands they inhabit. I also analyzed the

turtles’ use of biotic and abiotic habitat features and found many similarities between the spotted

turtles’ use of habitat in this fragmented area compared to other studies. This observational study

presents evidence that it is possible for spotted turtles to subsist on an annual basis in a small

fragmented habitat, meaning that some fragmented wetlands owned by enlightened individuals

may present viable options for repopulation of the species. However, a remaining concern for the

spotted turtle populations in fragmented habitats is their limited gene flow from other

populations. Further studies about gene flow may be necessary to determine if spotted turtle

populations in isolated wetlands have long-term stability.

Habitat Preference of the Spotted Turtle in a Micro-Urban Portion of the Southern Range, 2

Introduction

The spotted turtle, Clemmys guttata, is a semi-aquatic freshwater turtle that occupies a

broad range from southern Canada to parts of Florida (see Appendix 1 for a map of the range).

This species can be found in shallow, mud-bottomed habitats such as sphagnum swamps, cattail

marshes, sedge meadows, and drainage ditches2. To aid conservation efforts and further the

understanding of the sufficient conditions for the species’ survival, many researchers have

studied the spotted turtle’s behavior and habitat use. Many of these studies have been limited to

relatively unfragmented areas of the spotted turtle’s range such as in nature preserves, or have

been limited by the inaccessibility of private land. To expand the understanding of the ecology of

the spotted turtle in fragmented habitats, I performed an observational study on private land

affected by construction and development. In this report I describe the methods and results of the

study with an eye toward questions answered and unanswered about the needs of this beautiful

and endangered species.

Study Area

The study area is a private property in the mid-Atlantic coastal plain bordering the

Pamlico River in Washington, North Carolina. The wetlands where the study began are

approximately 0.09 hectares in size, are situated at an elevation ranging from 0 to 10 feet (3-4.6

m), and are about 10 to 15 meters away from the Pamlico River on one side. The wetlands are

surrounded by mowed grassland, as neighboring property owners have filled in the wetlands that

were previously on their property. Appendix 1 includes an image showing where wetlands were

in 1990 before housing development began in the area. Historically the area was farmland and

several drainage ditches remain on the undeveloped surrounding properties. Most of the


surrounding area that is not developed and is a mixture of reclaimed deciduous and coniferous

forest. The wetlands are subject to management by landowners who occasionally cut down small

saplings and remove debris after hurricanes. The wetlands become periodically inundated due to

hurricanes, and can be affected by storm surges up to several feet with violent wave action

known to tear off docks3. Using the online USDA soil survey, the soil was determined to be

Seabrook loamy sand. The study area receives an average rainfall of approximately 40 to 55

inches (101.6 to 139.7 cm) and has a “Bermuda High” pressure system leading to regularly

cloudless atmospheric conditions4. Rainfall is heaviest on average in July, August and

September5. The wetlands are determined to be freshwater, but the Pamlico River periodically

becomes brackish and supports typical saltwater wildlife such as rays, jellyfish, and dolphin3.

Primarily freshwater plant species are observed in the wetlands, providing further evidence for

the freshwater nature of the wetlands. The wetlands are characterized by a number of plant

species, including cattail, sedge, maple trees, bald cypress trees, river cane, bulrush, giant

cordgrass, duckweed, wax myrtle and sea myrtle. The study area also expanded to include

another portion of wetlands on another property 500 to 600 feet (152 to 182 meters) away from

the original study area. These wetlands include a small pond with deeper water than the first

study area. Areas of the second wetlands that are closer to the river resemble the first study area

but have been noted to support the narrow leaf cattail in addition to the broadleaf cattail. The

second study area also borders a drainage ditch. Appendix 1 shows the positions of these study

areas relative to each other.

Study Design, Materials and Methods

General Design Considerations


To begin, a number of careful decisions had to be made about the study’s design.

Treatments, controls and replicates were not considered feasible due to time and monetary

constraints, so a purely observational study of turtle movements was appropriate7. No mark and

recapture study was attempted due to the elusive nature of the species. A mark and recapture

study would require finding a number of spotted turtles at once, marking them, and then

recapturing a number of turtles again in another time frame. It is difficult enough to locate just

one turtle in a given day without using radio telemetry equipment, and using telemetry

equipment would violate the assumptions of the mark-recapture calculation8. Thus, only a

minimum value for the population can be put forth based on the number of total individuals

observed.

Tracking Technique

The spotted turtle is a shy species and is difficult to locate in the dense brush of the

wetland study area by visual inspection, which suggested that a study involving telemetry or

another tracking technique should be used instead of visual inspection. Studies on turtle

movements have used a variety of tracking methods, including string, isotope residues, radio

telemetry and satellite tracking. String presents a number of immediate problems, such as

tangling leading to predation or drowning, string breakage, interference with mating, and running

out of string. String seems to be a method best suited for tracking the turtle’s movements in a

small time frame such as a few hours or a day and has been used to track terrestrial box turtles9.

Radioisotope tracking presents fewer problems than string. Ward et al performed radioisotope

tracking using a tantalum-182 pin secured in a hole about 1mm cross in each turtle’s shell10. This

method required bringing the turtles to a laboratory and drilling the carapace of the turtle. No


such laboratory is available near this study area, and it was considered less invasive and less

likely to inadvertently injure the turtles if radio transmitters were attached using epoxy (Devcon,

and later PC-7). Radioisotope tracking was also ruled out due to the obvious health concern

about handling radioactive isotopes. Additionally, Ward et al also reported that turtles could be

detected as far as 10 meters away and that only 63% of tagged turtles were recaptured, whereas

in the current study, turtles could be detected as far as 182 meters away, the distance from the

first study area to the second, and 100% of the turtles were recaptured. Though radio telemetry

was a highly sensitive, effective, and safe alternative to radioisotope tracking, it presented one

significant limitation. Cochran and Litzgus use the rule of thumb that the mass of transmitters

should not be any greater than 5% of the mass of the turtle to prevent the transmitter from

impeding the movement or behavior of the turtle11,12. With this limitation in mind, a transmitter

had to be selected that was light enough to make several individuals viable for radio tracking.

The RI-2B 6-gram model produced by Holohil Systems was chosen to track the turtles in this

study, which was therefore suitable for turtles with masses over 120 grams. This meant that only

adult turtles could be tracked with radio telemetry; if juveniles were captured, they were

identified and their physical attributes and locations were recorded, however they could not be

regularly tracked. The average lifespan of the transmitter was 6 months and turtles tracked over

the entirety of the study had their transmitters changed at most seven times. Transmitters were

attached laterally on the carapace, in hopes of minimizing the transmitter’s possible interference

with mating. When transmitters were replaced, the new transmitter was installed on the opposite

side of the carapace so as not to inhibit growth in the same place (see Image 1).


Image 1. When transmitters were replaced, they were attached to the opposite side of the

carapace. Unfortunately, a thin layer of the outer shell was occasionally removed with the

transmitter, as indicated by the difference in coloration on the right side of the carapace of this

female subject.

Turtle Capture and Measurement of Physical Features

Turtles were collected first by visual inspection. When turtles were first identified, their

mass, carapace length, plastron length and shell height were recorded using a Pesola spring scale

and a Storm 6 inch digital caliper. Additionally the sex, physical features and health condition of

the turtle were noted. Sex was determined by secondary sex characteristics; males have brown

eyes and black chins whereas females have orange eyes and yellow or tan chins13. Additionally

males have a slightly more concave plastron than females. Checkups were repeated whenever a


transmitter was replaced to confirm that the turtles did not display any significant losses in mass

or any health problems that could be associated with the transmitter. Each turtle was also given

an identifying name or number; the two males and two females tracked were named Al, Tim,

Ms. 3, and Rachel respectively, and they will be referred to by their assigned names in this

report. Juveniles that were recaptured by visual inspection were also subject to checkups in order

to track their growth rate.

Turtle Recapture and Abiotic Measurements

Turtles fitted with transmitters were recaptured every 1 to 2 weeks from 2012 to 2015.

When turtles were recaptured, an orange construction flag with the identifying name of the turtle

and the date of recapture was placed to temporarily mark the position of the turtle. The water

depth, ambient temperature and water temperature were also recorded for each turtle’s location.

When the study began, ambient temperatures and water temperatures were measured from a

fixed point in the study area every time turtles were tracked, but later the ambient and water

temperatures at the exact position of the each turtle were recorded instead. In many cases turtles

would be in forms or under ice and thus water depth or temperature measurements could not be

recorded. The problems encountered with developing a consistent method of measurement for

abiotic factors in the environment made statistical inferences based on this data difficult. Data

was collected in mornings or afternoons, and no turtles were tracked at night.

Reporting Turtle Locations using an Arbitrary Coordinate System

Due to the small size of the study area, it was determined that greater accuracy in

measurement could be achieved by reporting turtle locations using an arbitrary coordinate system


instead of using GPS. WAAS enabled GPS is only accurate to about three meters and

preliminary studies with a GPS data logger showed GPS is subject to drift14. The arbitrary

coordinate system was constructed using two measuring tapes laid down on perpendicular sides

of the study area. The tapes were secured with ground staples to prevent shifting. Using these

axes, a turtle location could be recorded as a coordinate point. Within this coordinate grid, 15 by

15 foot quadrats were established in the study area. Recycled PVC posts were placed at the four

corners of each quadrat to mark the bounds of the quadrat. A total of 36 quadrats were produced

in a 6 by 6 quadrat square configuration, and were labeled A1 through F6, as shown in Figure 1.

Each quadrat was later characterized based on the three most abundant plants in the quadrat, the

relative water depth, and the shade level. In a time period less than one day, three water depth

readings in each quadrat were averaged and compared to the average water depth of other

quadrats to achieve a relative water depth measure. It was assumed that the water depths did not

change significantly in this time period. Shade level was described as sunny if there was no

shade in the quadrat, partly shady if there was some shade and some direct sun, and shady if the

quadrat was in complete shade.


Figure 1. An aerial view of the wetlands overlaid with an approximate outline of the

quadrats.

Expansion of Study Area Using GPS and Method of Calculating Home Range

As the study progressed, three of the four turtles tracked with transmitters periodically

left and returned to the initial study area. GPS points had to be used to determine the positions of

the turtles outside of the primary study area (Garmin GPS 72H model used). To incorporate GPS

points into the data collected using arbitrary (x,y) coordinates, I needed to make a number of

conversions. GPS points for turtles’ locations were collected first by establishing a GPS (0,0)

point at the edge of the wetlands that corresponds approximately with the (0,0) point on the

arbitrary axis. The distance in feet between a turtle’s location and the GPS (0,0) point could be

determined with the use of the FizzyCalc application (15). Using a relative distance between two

GPS points was intended to limit the drift observed in previous study with the GPS data logger.


A true north line was determined to be at a 51° angle to one axis of the arbitrary axis using

Google Earth. With an angle off of north and a distance between two points, the GPS data could

be converted to (x,y) coordinates using polar coordinate trigonometric equations.

Home range was described for each telemetered turtle using a minimum convex polygon

(MCP). The MCP is determined by connecting the points at the outermost positions of a turtle’s

observed home range with lines. Wolfram Alpha was used to calculate the area of the minimum

convex polygon by adding the areas of triangles that constitute the polygon17. Litzgus endorses

the MCP method for determining home range because it has historical prominence, graphical

simplicity, and reasonably good statistical stability16. She also states that the MCP method can be

biased by sample size such that a larger number of locations tends to result in a larger home-

range size estimate, and the estimate can include large areas never used by the animal16. I found

that the MCPs estimated for the turtles that left the primary study area include areas that the

turtles did not use regularly, such as the wet grasslands between the first and second study areas.

This is an unfortunate drawback of the MCP method, but due to the technological limitations of

this study, the MCP method was the most feasible approximation of home range. As Litzgus

noted, MCPs are widely used in the primary literature, making them a good choice to use when

comparing my data to that of others who have studied the spotted turtle.

Results and Discussion

Population Density Analysis

The current study captured a total of 10 turtles in a primary study area of approximately

0.09 hectares. Assuming that the turtles captured constituted the entire population of turtles in the

area the study suggests the population has a density of 111 turtles per hectare, a value larger than


that of any other known study. Three of the turtles in this study would periodically leave the

primary study area and travel to another wetlands, but other turtles did not demonstrate this

behavior over the course of the study. Thus when density was calculated, only the primary study

area was considered. The densities of turtles per hectare from a number of studies are compiled

and compared to the current study in Table 1.

Graham hypothesized that smaller wetlands maintain higher turtle density due to an

“edge effect”18. A possible explanation of Graham’s suggestion in the context of the current

study would be that the viable habitat for the turtles (the primary and secondary study areas) is

bounded on all sides by mowed lawns, which present hazards to turtles because they are more

vulnerable to predation and desiccation in these areas. Thus, the turtles do not regularly venture

out of the small area of habitat easily accessible to them, which leads to higher observed

population density. It is of interest to determine if the greater density of the population negatively

impacts the growth rate or adult mass of the turtles.

Table 1: Comparisons of population density. Part of Table 1 is collected from Graham’s 1995 paper, to which I added Graham’s data and my own.

Location Total Habitat (ha)

Estimated Total

Population

Total Captured Density per Ha

Year Reference

Dutchess Co. New York 15.59 - 155 9.35 1974-89 J. BehlerWill Co. Illinois 44 41 32 0.94 1988 Capler and Moll,

1988Cayuga Co. New York 2.83 30 26 10.6 1988 D. Collins

Lancaster Co. Pennsylvania 3.24 127 96 39.2 1967 Ernst, 1976 (19)Lancaster Co. Pennsylvania 3.24 233 155 71.91 1972 Ernst, 1976 (19)Lancaster Co. Pennsylvania 3.24 222 162 68.52 1973 Ernst, 1976 (19)Lancaster Co. Pennsylvania 3.24 258 180 79.63 1974 Ernst, 1976 (19)

Carroll Island, Maryland 3.24 - 1205 5.89 1970-73 Ward 1976 (10)Worchester County,

Massachusetts20.37-14.72 98 38 4.812-6.658 1989-1990 Graham, 1995

Eastern Costal North Carolina 0.09 - 10 111 2012-2015 Current Study


Growth Rate and Turtle Mass Comparisons

To investigate if the “edge effect” induced by land development led to stunted growth

and lower adult masses of C. guttata in the study, I compared the growth rate of juvenile turtles

and adult masses of turtles from my study to other studies. I found some evidence to suggest that

juveniles grew as fast as the juveniles in other studies and that adult turtle masses were smaller in

my study than studies at similar latitudes.

One juvenile estimated at 4 to 6 years old (using annuli as suggested by Cagle) was

identified in August of 2012 and was recaptured 607 days after in early April of 201421. While

this time span is greater than one year, it includes only one season from April to late June in

which spotted turtles are known to grow20, 21. The rest of the time turtles are generally inactive

due to aestivation and hibernation and are not feeding or growing. Cagle suggests that plastron

length better approximates a flat plane than the carapace and should therefore be preferred for

measuring growth rates21. The juvenile’s plastron length grew from 66.62mm to 74.41mm,

suggesting an annual growth rate of 7.80mm. Graham’s 1970 data from Rhode Island indicates

that spotted turtles had annual average plastron lengths (with ranges) of 48.80 (39.6-58.9) for

year 3, 54.89 (44.6-64.8) for year 4, 59.82 (48.5-70.1) for year 5, and 67.47 (53.1-83.8) for year

622. The difference in plastron length between each consecutive year is 6.09, 4.93, and 7.65 for 3

to 4, 4 to 5, and 5 to 6 years respectively. The 7.79 value from the current study appears to be

close to the 5 to 6 year growth rate from Graham’s study, which is consistent with the estimated

age range of the turtle. Even if the turtle was younger than 6 years, the growth rate of 7.79 is

larger than any other growth rate described by Graham, which supports the claim that the turtles

in the current study do not display a stunted growth rate. The similarity in values suggests that

the juvenile did not have a growth rate that was stunted compared to the Rhode Island population


but no statistical analysis of the data can be put forth due to small sample size19. Ernst estimated

a 2 to 3% annual growth rate in the plastron length of turtles in Pennsylvania until the turtle

reached 90mm19. Given a 2% annual growth rate I would expect my juvenile to grow from

66.6mm to 67.96, and given a 3% annual growth rate I would expect growth from 66.6mm to

68.6mm. The annual growth of my juvenile was 66.6 to 71.29 meaning that the turtle is growing

at least as fast or faster than those studied by Ernst. The data suggests that this juvenile does not

appear to be displaying stunted growth compared to other populations despite the small size of

the wetlands it inhabits and the high density of spotted turtles in the area.

This juvenile was recaptured again in March of 2015, 348 days after it was captured in

March of 2014. The plastron length changed by 6.79 mm, which is not as large as the 7.79 value

from the previous year, but is not smaller than 4.93, which suggests the turtle is not displaying

stunted growth.

Another juvenile estimated to be 4 to 6 years old was captured in March of 2014 and

again 203 days later in October 2014. This time period also includes one primary growth season.

The plastron length for this turtle grew from 72.04mm to 79.31mm. From this data the growth

rate is 7.27 mm per growth season, which is slightly lower than but close to the 5 to 6 year

growth rate range presented by Graham22. It does not appear possible to discern by the data if the

growth rate observed is somehow stunted in the case of this juvenile since the exact age of the

juvenile is uncertain.

Adult turtle masses from the four adult turtles (2 male, 2 female) tracked with

transmitters were recorded and compared to other studies as summarized in Table 2. The spotted

turtles of the current study have lower average masses for both males and females as compared

to the populations at similar latitudes investigated by Litzgus and Mousseau and O’Bryan23, 24.


The different sizes of study area may play a role in the difference between mean turtle masses

observed in the current study as compared to other studies at similar latitudes. The Francis

Beidler forest where Litzgus and Mousseau conducted their study was approximately 4500

hectares and the Weyerhaeuser property where O’Bryan conducted his study presented over

222,000 hectares of pine plantations and more than 10,000 km of ditch networks. These sizes

indicate that my study area is far smaller than those of studies at similar latitudes. While it is

difficult to tell if the size of the study area affects the mass of the spotted turtles living in it, a

similar pattern of observations appear at higher latitudes in the Georgian Bay study performed by

Reeves and Litzgus25. The island Georgian Bay turtles presented body masses that were

statistically significantly smaller than their mainland counterparts, and the island turtles had a

smaller area of viable habitat available compared to the mainland individuals. Reeves and

Litzgus thought that the difference in mean mass between the two populations could not be

reasonably attributed to an evolved dwarfism trait in the island population as a response to fewer

resources on the island because spotted turtles have a long generation time (approx. 25 yrs,

Litzgus 2004) and longevity (110 years for females)25, 26. Instead Reeves and Litzgus proposed

that founder’s effect may have played a role in the smaller size of the turtles, meaning that the

founding population of turtles on the island had a stochastically lower mean mass and that

restricted gene flow limited new variation in mean mass of the island population. Given that the

current study area was relatively recently (< ~25 years ago as evidenced by the development map

in Appendix 1) surrounded by a larger area of wetlands, Litzgus et al.’s reasoning suggests an

evolved dwarfism is not likely to explain the difference in body mass between the current study

and those at similar latitudes, but that the founder’s effect presents a plausible answer.


Table 2: Comparison of spotted turtle mean masses. Table 2 is reconstructed from tables produced by

O’Bryan (2014) and Reeves and Litzgus (2008) with the addition of the current study.

Location Mean Mass StudyMales Females

Francis Beidler Forest, SC 168 190 Litzgus and Mousseau (2004)

Georgian Bay (inland) ON 238.5(M & F combined) Litzgus unpubl. as reported in Reeves and Litzgus (2008)

Georgian Bay (island) ON 219.8 212.2 Reeves and Litzgus (2008)Weyerhaeuser Property, NC 156.3 173.8 O'Bryan Thesis (2014) >220,000 ha

Eastern NC 146.8 171.5 Current Study

Analysis of Home Range Data

Home range data of two males and two females have been collected over the course of

the study (see Appendix 1 for graphical representation of MCPs for each individual). An initial

question is, does home range change depending on available habitat? Researchers disagree about

this question. Graham suggests that turtles in marginal environments exhibit larger home ranges

because they need to travel farther to find suitable habitat and complete their annual cycles

(mating, nesting, aestivating and hibernating). In contrast, Litzgus and Mousseau23 found that

home range sizes do not tend to be larger in fragmented habitats because their study at the

relatively unaltered Francis Biedler Forest presented turtles with home-range sizes that were

larger than all other conspecific populations compared (see Table 3, cells highlighted in green).

Similarly, the home range size of turtles at the large (>222,000 hectares) Weyerhaeuser property

studied by O’Bryan presented large home range sizes, the largest recorded in Table 3 for males

and the second largest for females24. The current study presents small home ranges

corresponding to a small amount of available habitat, suggesting that home range becomes

smaller as available habitat becomes smaller.


The smallest home range observed was by a female (0.046 ha) and the largest by a male

(1.5 ha), but there is no clear trend in the data to suggest that males have a larger home range size

than females or vice versa. Furthermore the data of all past studies compared in Table 3 shows

that there is high variability in home range size and that males do not always have larger home

range sizes than females or vice versa. This may indicate that spotted turtles adapt their home

ranges to a specific landscape and do not have a generally applicable home range size. Some

researchers have proposed the reproductive strategies hypothesis to explain spotted turtle

movements, that is, researchers expect gravid (egg bearing) females to travel farther distances

during the nesting season and would expect males to travel farther during the mating season.

Females could not be identified as gravid, so no claim about their movement in the current study

can be put forward. The two largest movements made by males occurred in March, which is a

month considered part of the mating season. Tim moved and remained in the second study area

until mid-June, where he was found dead (cause of death unknown, predation suspected). Al

moved to an area with upland pine forest and another small wetlands behind a neighborhood

adjacent to the primary study area. It is suspected that these turtles moved in search of new

mates, but it cannot be said for certain.

Spotted turtles’ home ranges varied on an annual basis. For example, Al did not leave the

primary study area for the first two years of the study, leaving only in March of 2015. Similarly,

O’Bryan reported statistically significant evidence that spotted turtles have different home ranges

from year to year24. Why turtles vary their home range annually is unclear, though it may depend

on several factors such as variation is water depth (e.g. if there is a drought one year) or variation

in available food supply, as well as the motivation to search for new mates.


Table 4: Comparison of MCP Home Ranges. Table 4 is reproduced from Litzgus and Mousseau (2004) with added

recent studies as well as the current study. Cells highlighted in green are those from Litzgus and Mousseau

(2004).

Home Range Size (ha)Location Males Females Source

Francis Beidler Forest, SC 33°N 5.15 19.06 Litzgus and Mousseau, 2004Lancaster, PA 40° N 0.53 0.53 Ernst, 1970

Lockport IL 41° N 0.72 1.75 Wilson, 1994Romeoville, IL 42° N 0.99 0.58 E. McGee, E O. Moll, and D. Mauger, unpubl.

Cedar Swamp, MA 43°N 0.84 0.56 Graham, 1995Victoria Co., ON 44°N 2 4.7 Haxton and Berrill, 1999

Georgian Bay, ON 45°N 3.58 3.22 Litzgus, 1996Massachusetts 1.9 4.6 Milam and Melvin 2001

Ontario 2.1 1.3 Seburn 2012Weyerhaeuser Property, NC 37.3 12.2 O'Bryan Thesis1

Eastern North Carolina, 35°N 0.55, 1.5 0.046, 1.00 Current Study

Biotic and Abiotic Habitat Preference Data

Biotic and abiotic habitat use was determined primarily during the second year of the

study. Most statistics about habitat use are reported by excluding data from quadrats that contain

cavern-like structures called forms that spotted turtles use for aestivation and hibernation; this is

in an effort to eliminate the form data as a possible bias in the analysis.

During the second year the relative water depths of each quadrat were determined and

compared to the frequency of turtle visits in each quadrat using the Spearman rank correlation

coefficient (SRCC). The SRCC value determined was 0.48 (n=34, P<0.01), indicating that as the

frequency of turtle visits to a quadrat increased, the relative water depth of the quadrat tended to

increase as well. While the SRCC suggests a generally positive trend toward areas with deep

water, spotted turtles were not found regularly in extremely deep water. Instead they visited areas

1O’Bryan’s spotted turtles made extensive use of long ditch systems, which may explain part of the reason why his estimate is so unusually large, since the MCP may include large areas of non-ditch habitat that the spotted turtles do not actually use.


with a mean water depth of 12.4 ± 1.72 cm (99% confidence). This estimate is consistent with

other reports that spotted turtles prefer shallow habitats2, 27.

The relative shade level of each quadrat was recorded and a chi-squared goodness of fit

test was conducted on the frequency of turtle visits to quadrats based on the categories shade,

partial shade, and sunny. Excluding form data, the chi-squared test was significant (P<0.01),

indicating that the difference between the expected and observed values were too large to be

attributed to random sampling error. Figure 2 shows the observed and expected frequencies for

the corresponding categories and suggests that spotted turtles prefer quadrats with more sunlight.

Despite the high frequency of spotted turtle visits to quadrats with direct sunlight, spotted turtles

were not regularly found basking; instead they were mostly found buried deep in brush or mud,

occasionally in close proximity to Kinoternon subrubrum (eastern mud turtle).

Shade Partial Shade Sun0

20

40

60

80

100

120

C. Guttata Sunlight Preference

Observed

Homogenous Expected

Quadrat Categories

Freq

uen

cy o

f Tu

rtle

Loc

atio

ns


Figure 2. Sunlight preference of spotted turtles in the primary study area. An increasing trend

toward full sunlight may have caused the significance of the chi-squared test.

The turtles’ biotic preferences with regard to plants were also tested using chi-squared

analyses, and almost all of the tests were significant. The results of these tests suggest that

spotted turtles frequently visit areas with Typha latifolia (broadleaf cattail), Carex nigra

(rivercane), and Baccharis halimifolia (sea myrtle) more than expected, and they frequently visit

areas without Spartina cynosuroides (giant cordgrass), Myrica cerifera (wax myrtle), Taxodium

distichum (bald cypress) and Acer rubrum (red maple) less than expected. Expectations are based

on a homogenous model where every turtle would be expected to visit each quadrat equally as

often because it is assumed in the null hypothesis that turtle locations are independent of the

types of plants in the quadrats. Figure 3 shows an example of the kind of data analyzed of each

plant using the cattail data; there is a high frequency of turtle visits to areas with broadleaf

cattail, whereas there are relatively few visits to areas without cattails, which may explain why

the chi-squared test is significant. An environmental consultant studying the spotted turtle in

Suffolk County, New York suggested that spotted turtles prefer habitats with emergent

vegetation characterized largely by cattails in addition to phragmites and sedges (28). It appears

that the turtles in the current study use habitat similarly to those of the same species in other

studies despite the small portion of wetlands they primarily use.


With Cattails Without Cattails0

20406080

100120140160180200

C. Guttata Cattail Preference

Observed Fre-quencies

Expected Fre-quencies

Quadrat Locations

Freq

uen

cy o

f Tu

rtle

Vis

its

Figure 3. Spotted turtles’ use of quadrats with cattails versus without cattails in the primary

study area. Turtles tend to visit quadrats with cattails more than quadrats without cattails.

Note that correlations in biotic and abiotic data do not imply that these factors are the

cause of turtle movements. For instance, plant types present in the habitat may be correlated with

water depth or water quality. Additionally, shade level may be confounded with water depths

because tall trees shade the areas of the wetlands where there is little to no water. The current

study is purely observational and cannot make claims about causation with any certainty, though

I have offered some speculations.

The spotted turtles’ use of forms is an important feature when describing the species

preferred habitat. Forms function as a protected area for aestivation and hibernation. Litzgus et

al. have found that spotted turtles use forms with water (an illustration of the types of forms they

found is reproduced in Appendix 1), whereas others such as Harms have described dry form use

29, 30. In the current study, spotted turtles were known to use two forms for both aestivation and

hibernation. One form bordered the edge of the primary study area in quadrat F6 and the other


form was in quadrat E4. Both forms were wet. On one day a waterproof plumbing inspection

camera was used to determine internal structure of the F6 form. A spotted turtle shell was

identified briefly on the camera’s display inside the form, however the turtle could not be

identified nor was a transmitter visible on it. The ceiling of the F6 form was made from a

decomposing tree stump and a large, layered root system, while the floor of the form was a soft

mud bottom. Less is known about the E4 form, but it is also wet. In a rare case where the turtles

could be found inside the E4 form, two turtles, Al and Rachel, were found almost on top of each

other inside the form. It was unclear if they were mating or were merely occupying the same

form in close proximity, but mating inside forms has not been reported nor would it be expected

since aestivation and hibernation are recognized as distinct seasons from mating for this species.

Conclusion

The spotted turtle is a species that shows a preference for an early successional wetland

habitat with shallow standing water. Populations of spotted turtles are in decline due to a number

of factors that may include habitat loss due to natural succession and human development as well

as trafficking and poaching motivated by the pet trade. Despite the potentially bleak future of this

species, the current study suggests that spotted turtles have the capacity to adjust their home

range and habitat use to a small or fragmented habitat. This provides a possible means for

enlightened homeowners with small wetlands on their property to aid in the conservation of this

endangered species. A remaining concern is whether small populations are unstable or

vulnerable to decline due to limited gene flow and inbreeding. With limited introduction of new

genetic variation, the turtles may be less capable of maintaining a stable population in the long

term. Future studies to consider the stability of isolated populations and effective methods of


introducing genetic variation are necessary for a complete picture of what conservation methods

will help this endangered species.

Acknowledgements

I would like to thank Cheryl and Timothy McGuire for their continued support of my

project, and for their aid in collecting the flag point data during the project, a task I certainly

could not have done alone. They generously funded the project.

I would also like to thank Kelly Davis, former US Fish and Wildlife biologist and native

plant expert, for her assistance in characterizing my study area. I also owe thanks to the

professionals who have advised me on the methods, data analysis and conceptual models for my

project, including Jeff Hall (NC Wildlife), Chris O’Bryan, Jeff Beane (NC Museum of Natural

Science) Dr. Joshua Beattie and Dr. Kim Failor.


Appendix 1


Above: Study areas depicted in a map from 1990. The large arrow indicates the direction of

North. The primary study area is on the rightmost lot labeled with a circled 1. The secondary

study area is on the property labeled with a circled 6. All of the wetlands corresponding to lots

labeled 2 through 5 have been mowed and are now wet grassland.

Above: A map of the spotted turtles’ known range, reproduced from Ernst and Lovich’s Turtles

of the United States and Canada.


Above: An illustration reproduced from Litzgus et al.’s 1999 paper Phenology and ecology of

hibernation in spotted turtles (Clemmys guttata) near the northern limit of their range. Forms in

the current study highly resemble those of Figure 2 A in this illustration.


Minimum Convex Polygons

Below are the four minimum convex polygons calculated from locations using GPS and

arbitrary (x,y) coordinates adjusted to be on the same axes. The (x,y) area that corresponds to the

primary study area is within 100 feet of the (0,0) mark in the x and y direction. The triangles

formed by the lines were added together to determine the area of the MCP, but the triangles do

not indicate the movements of the turtles. Note the scale of the axes of the graphs are not the

same.

Above: Minimum convex polygon for Tim. Total area calculated was 59,495 square feet, or 0.55

hectares. Tim was found deceased in the second study area on a particularly hot (40°C) day and

could not longer be tracked after 6/11/14.


Above: Minimum convex polygon for Al. Al left the primary study area and moved to an upland

pine forest with a nearby wetland between 3/9/15 and 3/18/15 for the first known time in the

course of the study, which began on 1/4/12.


Above: Minimum convex polygon for Ms. 3. Ms. 3 moved to the second study area on 5/19/12,

remained there until 7/6/12, and then was located again in the primary study area on 7/25/12.

Ms. 3 could not be located from 9/7/13 to 10/18/13 (no transmitter sound could be heard in any

direction) but was relocated in the primary wetlands on 10/27/13.


Above: Minimum convex polygon for Rachel. Rachel was never documented leaving the primary

study area. However, given that other individuals moved only after several years there is reason to

suspect that Rachel may leave the primary wetlands as well on rare occasions.


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