J. Zool., Lond. (2005) 267, 397–404
C 2005 The Zoological Society of London
Printed in the United Kingdom
doi:10.1017/S0952836905007533
A comparative study of environmental factors that affect nesting
in Australian and North American freshwater turtles
Kenneth D. Bowen*, Ricky-John Spencer and Fredric J. Janzen
Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, Iowa, 50011, U.S.A.
(Accepted 16 March 2005)
Abstract
The timing of reproductive events is critical for fitness, and these events are often linked to weather and climate.
Weather components are thought to influence the nesting behaviour of freshwater turtles, but to date there have
been few quantitative studies and no comparative studies. We compared the environmental cues used by nesting
Australian (Emydura macquarii and Chelodina expansa) and North American (Chrysemys picta) freshwater turtles,
and quantified the differences in weather between days with and without nesting activity within the nesting season.
We also characterized the diel time of nesting for each species. The results suggest that nesting behaviour is related
to warm air and water temperatures in C. picta and to rainfall in E. macquarii and C. expansa. Chrysemys picta
primarily nests in the afternoon and evening, E. macquarii is a crepuscular nester, and C. expansa nests diurnally.
While changes in life history resulting from climate change are difficult to predict, we suggest that an increase
in the number of El Niño events may have adverse effects on the two Australian species, whereas increases in
environmental temperature may expand the number of nesting opportunities for C. picta.
Key words: Emydura, Chelodina, Chrysemys, weather, life history
INTRODUCTION
The schedule of reproduction at various temporal scales
has substantial fitness ramifications. The relative timing
of reproductive events within the appropriate season and
even within a single day is often critical to reproductive
output and success. For example, reproductive success
of male Douglas firs Pseudotsuga menziesii is dependent
upon phenological overlap with females during the first
two-thirds of the breeding season (Burczyk & Prat,
1997), and male garter snakes Thamnophis sirtalis
that mate with females first can ‘enforce chastity’
by placing a copulatory plug in the female’s cloaca
(Devine, 1975; Shine, Olson & Mason, 2000). Similarly,
the timing of propagule dispersal can reduce parental
energy expenditure (Congdon & Gatten, 1989) or direct
exposure to predation (Tucker, Filoramo & Janzen,
1999), minimize the probability that oviposition sites are
detected by predators (Burger, 1977), swamp dispersers or
predators with propagules (Eckrich & Owens, 1995), and
increase the probability of post-hatch offspring survival
(Warner & Andrews, 2003). Given these consequences
for fitness, identifying potential mechanisms underlying
temporal patterns of reproduction provides crucial
* All correspondence to: K. D. Bowen.
E-mail: hideneck@yahoo.com
information for understanding this fundamental aspect of
living organisms.
Weather and climate are often linked to both the initiation of the breeding season and the timing of reproductive
events within the breeding season. For instance, courtship
and nesting in many birds (Heffelinger et al., 1999;
Whitehead & Saalfield, 2000) and turtles (Seabrook, 1989;
Burke, Gibbons & Greene, 1994; Wilson, Mushinsky &
McCoy, 1999) is stimulated by rainfall. Environmental
temperatures affect the onset of the nesting season in some
birds (MacInnes et al., 1990), the onset of the breeding
season in many amphibians (Gibbs & Breisch, 2001), and
the interval between nesting events in sea turtles (Solow,
Bjorndal & Bolten, 2002). The links between weather,
climate, and reproductive events may be impacted by both
direct and indirect effects of global warming (Janzen,
1994; Parmesan & Yohe, 2003; Root et al., 2003).
Several authors have suggested a connection between
weather conditions and the nesting behaviour of freshwater turtle species. Obbard & Brooks (1987) found
that the onset of the snapping turtle Chelydra serpentina
nesting season is related to spring water temperatures
in Quebec. Christens & Bider (1987) found that the
onset of the painted turtle Chrysemys picta nesting
season in Quebec is related to ambient temperature in
summer of the previous year. Iverson & Smith (1993)
and Rowe, Coval & Campbell (2003), however, found
that onset of the C. picta nesting season in Nebraska and
398
K. D. BOWEN, R.-J. SPENCER AND F. J. JANZEN
Michigan, respectively, is related to ambient temperatures
in spring of the current year. Red-eared sliders Trachemys
scripta elegans in Illinois seem to nest in response
to rainfall and increased temperatures (Tucker, 1997),
whereas striped mud turtles Kinosternon baurii in Florida
(Wilson et al., 1999), common mud turtles Kinosternon
subrubrum in South Carolina (Burke et al., 1994), and
the broad-shelled turtle Chelodina expansa in Australia
(Georges, 1984; Booth, 2002; McCosker, 2002) emerge in
response to rainfall. To date, however, there are no studies
that quantify a variety of environmental cues to compare
nesting behaviour among multiple species of freshwater
turtles. Such studies might yield insight into the lifehistory evolution of the species involved and aid in the
prediction of the effects of climate change on turtle
populations.
In the current study, the nesting behaviour of three
species of freshwater turtle was compared to determine
how they respond to weather conditions. Specifically, the
behaviour within the nesting season was examined in an
effort to identify the environmental cues that females use
as signals to emerge from the water to nest. Three species
were compared: Emydura macquarii and Chelodina
expansa are sympatric in the Murray River of Australia
and Chrysemys picta is widespread in North America.
Several hypotheses were tested using this comparison.
First, it was hypothesized that E. macquarii and C. picta
would respond similarly to environmental cues because
they have similar life histories: both species nest in
spring/summer, are omnivorous, and prefer to live in
slow-moving or stagnant water (Ernst, Lovich & Barbour,
1994; Cann, 1998). Accordingly, it was hypothesized that
C. expansa might respond differently to environmental
cues than the other two species because it nests during a
cooler time of year (autumn; Cann, 1998). Also, embryos
of C. expansa undergo a period of secondary diapause
and prolonged incubation (Booth, 1998, 2000, 2002).
Finally, based on observations made in the field, it was
hypothesized that all three species would use rainfall as a
cue for nesting.
MATERIALS AND METHODS
Study animals and field methods
Australia
The Murray short-necked turtle Emydura macquarii is a
widespread chelid turtle (suborder Pleurodira) inhabiting
the Murray–Darling drainage system, with several forms
distributed throughout eastern flowing rivers of coastal
New South Wales and Queensland. Emydura macquarii
nests from late spring into summer (October–December;
Cann, 1998). The broad-shelled turtle Chelodina expansa
is the largest freshwater chelid in Australia, and is
sympatric with E. macquarii throughout much of its range.
Chelodina expansa nests in autumn (March until May;
Cann, 1998) at the site used in this study.
Study sites were located in the upper Murray River near
Albury, New South Wales (36. 0863◦ S, 146.9223◦ E; see
Spencer, 2002a,b; Spencer & Thompson, 2003 for full
description). Nocturnal and diurnal searches for female
E. macquarii were conducted from late October to midDecember from 1996 to 1998 (see Spencer, 2002a for
more detail). Searches did not occur for up to 7 days in
1996 and 1997 at the beginning of November, as eggs
were transported to the University of Sydney for a separate
experiment (these days were not included in any analyses).
Nocturnal and diurnal searches for female C. expansa
were conducted from late March to late April in 1997 and
1998.
Water temperatures were measured daily using a
maximum–minimum thermometer placed at a depth of
20 cm in at least 2 lagoons during the nesting season.
Weather data, including daily maximum and minimum
air temperatures, long-term average maximum and
minimum air temperatures, daily precipitation, weather
condition at 09:00, 12:00, and 15:00 (rain, clear overcast,
thunderstorm), and air temperature at 09:00, 12:00, and
15:00, were obtained from the Australia Bureau of
Meteorology (2004).
North America
The painted turtle Chrysemys picta is a small to mediumsized freshwater turtle (suborder Cryptodira) that ranges
from southern Canada to the Gulf of Mexico and from
the Atlantic to the Pacific Oceans (Ernst et al., 1994).
Chrysemys picta nests from late spring to mid-summer
(May–July in most areas; Ernst et al., 1994). From this
point onward, seasons rather than months are referred
to when comparing species because of the difference in
timing of seasons between hemispheres. Data presented
here represent a portion of a long-term study of the
nesting ecology of the painted turtle (Janzen, 1994) at
the Thomson Causeway Recreation Area (TCRA) near
Thomson, Illinois, U.S.A. (41.9514◦ N, 90.1165◦ W). The
Thomson Causeway is a c. 450 × 900 m island on the
eastern bank of the Mississippi River, and it contains a
c. 1.5-ha nesting area that is bordered on the east side by
a 200-m wide slough from which most turtles emerge to
nest. The site is managed and maintained by the United
States Army Corp of Engineers (USACE; see Kolbe &
Janzen, 2002 for a more complete site description).
The nesting beach at TCRA was monitored for nesting
turtles from early June to late June in 2001 and from late
May to early July in 2002 and 2003. The nesting beach
was searched for females once every hour from dawn
until dusk. In each year, nesting females were observed
leaving the water, constructing nests, and laying eggs. All
nests were excavated in autumn to count hatchlings; so
false nests were identified and removed from the dataset
before analysis. Weather data was obtained for the nesting
season from the USACE Lock and Dam 13 c. 12 km
south of the study site. Data included daily maximum and
minimum air temperatures, long-term average maximum
and minimum air temperatures, daily precipitation, and
water temperature.
Freshwater turtle nesting behaviour
Data analysis
The weather conditions of nesting and non-nesting days
were compared within the nesting season (maximum and
minimum air temperature, water temperature, precipitation, the change in maximum and minimum air temperatures from the previous day, and the change in maximum
and minimum air temperatures from the long-term average
for a given day; air temperature and day condition at
09:00, 12:00, and 15:00 were included for Australian
species only) using non-metric multidimensional scaling
(nMDS), calculated with the software package PRIMER
(Clarke, 1993). nMDS yields a map-like output in which
the relationships among nesting observations can be compared: the nearer the points on the map are to one another,
the more similar the nesting patterns. How well the points
in space match the actual distance between data points
can be measured by stress statistics: stress values < 0.2
give a useful 2-dimensional representation of the data
(Clarke & Warwick, 1994). Differences in weather conditions between nesting and non-nesting days were also
looked for using analysis of similarities (ANOSIM),
a multivariate non-parametric analogue of ANOVA
(Clarke & Greene, 1988). SIMPER, an analysis that calculates the average Bray–Curtis distance between all pairs of
inter-group samples (i.e. distance between each variable
for nesting and non-nesting days), was used for post-hoc
comparisons. The SIMPER module (Clarke & Warwick,
1994) identifies environmental factors that make an individual contribution of > 2% to the ANOSIM result. The
same statistical methods were used to compare among species. In addition to these comparisons, the diel time of nesting for all species was characterized by plotting the number of turtles observed nesting at different times of day.
Turtles are known to retain fully developed eggs for long
periods while apparently waiting for suitable nesting conditions (Galbraith, Graesser & Brooks, 1988; Buhlmann
et al., 1995), and female E. macquarii have been
artificially induced to oviposit up to 2 weeks before the
onset of nesting on the Murray River (Spencer, 2001). In
our comparisons of nesting vs non-nesting days, weather
data for up to 2 weeks before the first turtle observed
nesting was therefore included in addition to data for nonnesting days throughout the nesting season. Data were
standardized (to a mean of 0 and standard deviation of 1)
before analysis to remove any effect of different scales
of measurement for the different variables (Legendre &
Legendre, 1998).
RESULTS
Comparison of nesting vs non-nesting days
Differences in climate during the nesting period relate to
season, but comparing the weather conditions of nesting
vs non-nesting days determines environmental preferences
(and avoidances) of species within the season. Seventy-six
E. macquarii nests from 33 nesting days, 29 C. expansa
nests from 22 nesting days, and 504 C. picta nests from
399
Table 1. SIMPER analysis of dissimilarity of weather conditions
during nesting and non-nesting days for Emydura macquarii.
Change in daily MAX and MIN, change in maximum and minimum
temperatures from the previous day, respectively, for a given day
during the nesting season; change in average MAX and MIN,
change in maximum and minimum temperatures from the long-term
average for a given day during the nesting season. Only climate
conditions that contributed substantially to differences between
nesting and non-nesting days are displayed (see text for more detail)
Average value
Variable
Nesting
Nonnesting
Rainfall (mm)
Change in daily MAX (◦ C)
Change in daily MIN (◦ C)
Change in average MIN (◦ C)
MIN (◦ C)
Air temperature at 15:00 (◦ C)
MAX (◦ C)
Change in average MAX (◦ C)
5.6
−1.1
0.6
2.0
12.2
22.5
24.3
−1.2
0.3
0.6
0
−0.5
9.8
24.3
25.7
0.2
Average
contribution
(%)
15.3
14.0
11.7
10.1
9.7
9.5
8.7
8.7
93 nesting days were used in our analyses. Multidimensional scaling of environmental variables produced a plot
with good separation of nesting and non-nesting days and
a good stress value for all species. Weather conditions
differed significantly between nesting and non-nesting
days for all species (E. macquarii, nMDS stress = 0.09,
ANOSIM global R = 0.20, P = 0.001; C. expansa, nMDS
stress = 0.08, ANOSIM global R = 0.31, P = 0.001; C.
picta, nMDS stress = 0.1, ANOSIM global R = 0.48,
P = 0.001). Rainfall made the greatest contribution to
the dissimilarity between nesting and non-nesting days
in E. macquarii (15%). Emydura macquarii individuals
preferred to nest during or after rainfall. Minimum air
temperatures were slightly warmer and maximum air
temperatures slightly cooler than the previous day and
the long-term average (Table 1). Similarly, C. expansa
individuals generally nested during or shortly after rain,
although changes in air temperatures contributed greatest
to the dissimilarity between nesting and non-nesting
days, with turtles avoiding cooler days with below
average temperatures (Table 2). In contrast, temperature
related variables, rather than rainfall, make the greatest
contribution to the dissimilarity between nesting and
non-nesting days in C. picta (> 80%; Table 3). The
air temperature on nesting days was c. 7 ◦ C warmer
than non-nesting days, and the water temperature on
nesting days was c. 5 ◦ C warmer. The air temperature
on non-nesting days was generally 5 ◦ C below the longterm average (Table 3). Once the nesting season began,
C. picta individuals were observed nesting almost every
day throughout the nesting season, whereas the two
Australian species nested more sporadically (Fig. 1).
Comparison among species
Multidimensional scaling of environmental variables on
days of nesting produced a plot with a separation of species
400
K. D. BOWEN, R.-J. SPENCER AND F. J. JANZEN
Table 2. SIMPER analysis of dissimilarity of weather conditions
during nesting and non-nesting days for Chelodina expansa. Change
in daily MAX and MIN, change in maximum and minimum
temperatures from the previous day, respectively, for a given day
during the nesting season; change in average MAX, change in
maximum temperature from the long-term average for a given day
during the nesting season. Only climate conditions that contributed
substantially to differences between nesting and non-nesting days
are displayed (see text for more detail)
Average value
Variable
Nesting
Nonnesting
Change in average MAX (◦ C)
Change in daily MAX (◦ C)
Rainfall (mm)
Temperature at 15:00 (◦ C)
MAX (◦ C)
Change in daily MIN (◦ C)
MIN (◦ C)
0.4
0.6
6.3
23.7
24.7
0.4
9.3
−3.1
−0.6
0.0
20.0
21.7
−0.3
6.9
Average
contribution
(%)
12.7
11.5
11.4
10.8
10.8
10.7
10.0
Table 3. SIMPER analysis of dissimilarity of climate conditions
during nesting and non-nesting days for Chrysemys picta. Change
in daily MAX and MIN, change in maximum and minimum
temperatures from the previous day, respectively, for a given day
during the nesting season; change in average MAX, change in
maximum temperature from the long-term average for a given day
during the nesting season. Only climate conditions that contributed
substantially to differences between nesting and non-nesting days
are displayed (see text for more detail)
Average value
Variable
Nesting
Nonnesting
Change in daily MAX (◦ C)
Change in daily MIN (◦ C)
MIN (◦ C)
MAX (◦ C)
Change in average MAX (◦ C)
Water temperature (◦ C)
0.9
0.4
15.4
26.4
1.1
21.5
0.2
−0.4
8.6
18.4
−3.8
16.7
Average
contribution
(%)
19.3
18.3
17.3
13.3
10.8
10.8
1
Proportion of days
0.8
0.6
0.4
0.2
0
Emydura macquarii
Chelodina
expansa
Chrysemys
picta
Species
Fig. 1. Proportion of days that turtles were (white portion of bars)
or were not (grey portion of bars) found nesting during the entire
nesting season. Days included were from the first turtle observed
nesting until the last turtle observed nesting.
and a reasonable stress (0.15). There was a statistically
significant difference in the weather conditions of
nesting days between species (ANOSIM global R = 0.33,
P = 0.001). Both of the Australian species were likely
to nest under a wider variety of weather conditions than
C. picta, and nested under different weather conditions
than C. picta overall (ANOSIM global R = 0.30, P =
0.001 for E. macquarii; ANOSIM global R = 0.49, P =
0.001 for C. expansa). There was only a minor difference
in the weather conditions of nesting between E. macquarii
and C. expansa (ANOSIM global R = 0.07, P = 0.05)
despite these species nesting in different seasons.
Both E. macquarii and C. expansa individuals tend to
nest when it is raining and maximum air temperatures
are lower than the day before. Because E. macquarii
individuals nest in spring, maximum and minimum air
temperatures are greater than for the autumn-nesting
C. expansa. The primary difference in nesting weather
between the Australian species and C. picta seems to be
rainfall: the Australian species generally nest during or
after rain (cf. Tables 1 & 2 to Table 3).
Diel time of nesting
Emydura macquarii has a bimodal daily nesting activity
with peaks occurring near dawn and dusk (Fig. 2a).
Chelodina expansa individuals were observed nesting
only during daylight hours (Fig. 2b). Chrysemys picta
individuals nest throughout the day with peak activity
several hours before dusk (Fig. 2c).
DISCUSSION
The timing of reproductive events within the reproductive
season has wide-ranging fitness ramifications. Reproduction early or late in the breeding season is related to
survival and fecundity of adults (Brinkhof et al., 2002)
and the survival of offspring (Einum & Fleming, 2000).
The timing of reproduction with respect to unpredictable
environmental factors within the reproductive season may
affect the probability of reproducing successfully and
can have indirect effects on fecundity (Thorhallsdottir,
1998; Satake, Sasaki & Iwasa, 2001). Describing the
timing of reproductive events in relation to environmental
conditions within the reproductive season is thus a critical
component of the study of life-history evolution.
Emydura macquarii and C. expansa respond strongly to
rain and the air temperature changes associated with rain,
usually emerging to nest during or after storms. Contrary
to our expectations, this behaviour differs from that of
C. picta, which respond to air and water temperature
by predominantly nesting when temperatures are at or
above average during the nesting season. How do these
differences provide insight into life-history evolution of
these species?
The nesting behaviour of C. picta in response to
environmental cues may be explained by the thermal
energy needed for successful nesting. Chrysemys picta
Freshwater turtle nesting behaviour
401
10
(a)
9
8
7
6
5
4
3
2
1
6
02:00
00:00
22:00
20:00
18:00
16:00
14:00
12:00
10.00
08.00
06.00
04.00
0
(b)
5
Turtles (n)
4
3
2
1
00:00
02:00
00:00
02:00
22:00
20:00
18:00
16:00
14:00
12:00
10:00
08:00
06:00
04.00
0
(c)
120
100
80
60
40
20
22:00
20:00
18:00
16:00
14:00
12:00
10:00
08:00
06:00
04:00
0
Time
Fig. 2. Daily nesting activity of (a) Emydura macquarii, (b) Chelodina expansa and (c) Chrysemys picta. The white portion of the bar
underneath the histogram corresponds to daylight hours during the nesting season.
402
K. D. BOWEN, R.-J. SPENCER AND F. J. JANZEN
may require warm morning and midday temperatures for
basking before nesting in the afternoon. Basking functions
in thermoregulation (Boyer, 1965; Crawford, Spotila &
Standora, 1983; Schwarzkopf & Brooks, 1985), drying
and ectoparasite removal (Cagle, 1950; Neill & Allen,
1954; Boyer, 1965), digestive facilitation (Moll & Legler,
1971), vitamin D synthesis (Pritchard & Greenhood,
1968), and may aid in eggshell development before nesting. Evening temperatures at TCRA can be highly variable
and several turtles were observed stranded overnight on
the nesting beach during cool evenings. Increased body
temperature from basking may hasten nest construction
and reduce the amount of time spent on land by a female.
It is possible that any day that is warm enough to obtain
sufficient thermal energy for nesting is suitable. Once
ambient temperatures are warm enough for the nesting
season to begin, factors other than weather may be driving
the decision to emerge and nest. This hypothesis would
explain the fact that very few days lack nesting turtles
once the nesting season begins for C. picta.
Unlike C. picta, rainfall seems to be a critical determinant of nesting behaviour within the nesting season
for E. macquarii and C. expansa. Rain may soften the
ground and make nest excavation easier and thus faster
(Seabrook, 1989), minimizing the time that turtles spend
on land and are exposed to predators. Water may also
play an important role in nest construction. During excavation, female C. expansa and E. macquarii release fluid
from their cloaca (Goode & Russell, 1968), presumably
to soften the substrate. Predators use both visual and
olfactory cues to detect nests (Spencer, 2002a) and nesting
during rain may have the dual effect of diluting body
fluid (i.e. urine and scent trails; Burke et al., 1994)
and disguising the nest by compacting loose soil or
disturbing the ground surrounding the nest. Rain would
also minimize evaporative water loss of nesting turtles
(Wilson et al., 1999). Because many of these factors could
also benefit C. picta, we are currently unable to explain this
difference between the turtle species. However, consistently high levels of nest depredation at the Australian
sites (Spencer, 2002a; Spencer & Thompson, 2003)
compared to fluctuating levels at TCRA (Kolbe & Janzen,
2002) and different nest predators at the sites (primarily
fox Vulpes vulpes in Australia and raccoon Procyon lotor
at TCRA) may be responsible.
Each species nests during different periods of the day.
Nesting of C. expansa in northern Australia is also
associated with rainfall (Georges, 1984; Booth, 2002;
McCosker, 2002) and occurs during the day (Georges,
1984). Emydura macquarii are associated with nesting
during the evening after rain as well (Green, 1996). Peak
nesting occurs in the afternoon or evening hour in C. picta
(Congdon & Gatten, 1989; Rowe et al., 2003). The diel
nesting activity of C. picta is probably linked to basking
activity, as discussed earlier. However, the differences in
diel activity between the two Australian species may be
more difficult to interpret. Spring–summer storms usually
occur in the late afternoon in south-eastern Australia
(Australia Bureau of Meteorology, 2004) and nesting of
E. macquarii individuals generally occurs en masse in
discrete areas close to shore (Spencer, 2002a) throughout
the night and into the following morning. Chelodina
expansa nest individually much farther from shore than
E. macquarii (Georges, 1984; Spencer & Thompson,
2004) and diurnal nesting may simply embody the process
of finding an adequate nesting site and returning to the
water. Diel activity may also reflect different strategies of
predator avoidance, as E. macquarii is known to avoid
predators during nesting (Spencer, 2002a; Spencer &
Thompson, 2003).
It is difficult to predict the precise effects of climate
change on life history evolution, in part because
physiological or genetic constraints may prohibit or
minimize climate-driven changes in any particular lifehistory trait (Winkler, Dunn & McCulloch, 2002).
However, the close coupling of the nesting of Australian
turtles with rainfall events suggests that a decrease in
rainfall may adversely affect the reproduction of these
animals. This finding is important considering that El
Niño–Southern Oscillation (ENSO) events result in dry
conditions in Australia. If the frequency and intensity of
ENSO events continue to increase (Trenberth & Hoar,
1997), the decreasing occurrence of storms and rain
may adversely affect E. macquarii and C. expansa by
delaying nesting, making nest construction more difficult,
or making nests more conspicuous to predators. It is well
known that global temperatures are increasing (IPCC,
2001), and while this warming may adversely affect the
sex determination of C. picta (Janzen, 1994), little effect
on the nesting behaviour of this species is anticipated
within the nesting season. At this time, some C. picta
individuals emerge on almost every day of the nesting
season. Rising temperatures are unlikely to alter this
pattern because average or above average temperatures
characterize nesting days. An interesting avenue for future
study would be to determine if temperature increases
affect the initiation and duration (i.e. number of clutches)
of the nesting season of C. picta. The implications of
such a change for reproductive energetics and population
dynamics could be substantial.
Phylogeny has not been considered in these comparisons, and our interpretations are therefore tentative.
For example, the similarities and differences in nesting
behaviour discussed here could result from phylogenetic
constraint. Future studies should focus on addressing this
possibility by adding more species to the comparison
and then adopting analytical approaches that specifically
incorporate phylogenetic relationships. We also advocate
continued monitoring of these and other populations of
freshwater turtles and their responses to weather. Such
long-term studies may provide valuable insight into the
effects of climate change on natural systems.
Acknowledgements
We thank the U.S. Army Corps of Engineers for continued
access to the Illinois field site and the Janzen Lab
turtle camp crews from 2001 to 2003 for helping with
data collection at this site. The research in Illinois was
Freshwater turtle nesting behaviour
conducted under approved animal care protocol 1-14733-J from Iowa State University and by permission of
the U.S. Fish & Wildlife Service (2001 permit 3257601017; 2002 permit 32576-02024; 2003 permit 3257603014) and the Illinois Department of Natural Resources
(2001 permit NH-01.0073; 2002 permit NH-01.0073;
2003 permit NH-01.0073). Funding for this part of the
study was provided by NSF grants DEB0089680 and
IBN0080194 to FJJ. Research in Australia was supported
by a Reserves Advisory Committee Environmental Trust
Grant and an Australian Research Council Small Grant,
and was conducted under New South Wales National Parks
and Wildlife Service permit B1313, New South Wales
Fisheries License F86/2050, and University of Sydney
Animal Care and Ethic Committee approval L04/1294/2/2017. We thank M. Thompson for support during
this part of the study, as well as the Webb, Griffith, and
Delaney families, R. Ruwolt, and Z. Ruwolt for their
support and use of their property. KDB acknowledges
the support of an Iowa State University Graduate College
Fellowship.
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