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Evaluation of predator-exclusion cages used in turtle conservation: Cost analysis and effects on nest environment and proxies of hatchling fitness


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Context A main goal of conservation is to mitigate anthropogenic impacts on natural ecosystems, thus conservation tools themselves should not negatively affect target species. Predator-exclusion cages are effectively used to reduce predation of turtle nests; however, their effects on nest environment and developing hatchlings have not been examined. Aims Our study had the following four goals: (1) to examine effects of cages on the nest environment, (2) determine whether nest caging affects proxies for hatchling fitness, (3) evaluate whether nest predators preferentially interact with certain cage types, and (4) assess the cost-effectiveness of different nest caging designs. Methods In 2010 and 2011 in Algonquin Provincial Park, Ontario, painted turtle (Chrysemys picta; n≤93) and snapping turtle (Chelydra serpentina; n≤91) nests were assigned to one of three treatments (wooden-sided cages, above- and below-ground wire cages) or a control (no nest cage) and outfitted with a data logger to record incubation temperature. After emergence, hatching success and proxies of hatchling fitness were measured. Key results Nest temperature, hatching success, frequency of hatchling deformities and locomotor performance did not differ among cage treatments. However, hatchling body condition differed among treatments; wooden-sided and below-ground cages had the most positive influence on body condition in painted and snapping turtles, respectively. Predator interactions did not differ among treatments, and wooden-sided cages were the most inexpensive to construct. Conclusions Nest cages did not alter the nest environment from natural conditions but did alter hatchling body condition, and nest caging affected species differently. Implications Nest cages are known to reduce nest depredation, and our data indicated that, in general, nest cages also do not affect the nest environment or proxies for hatchling fitness. Thus, our findings indicated that cages are effective conservation tools that do not present secondary deleterious effects on potential recruitment.
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Evaluation of predator-exclusion cages used in turtle
conservation: cost analysis and effects on nest environment
and proxies of hatchling tness
J. L. Riley
and J. D. Litzgus
Department of Biology, Laurentian University, 935 Ramsey Lake Road, Sudbury, Ontario, P3E 2C6, Canada.
Corresponding author. Email:
Context. A main goal of conservation is to mitigate anthropogenic impacts on natural ecosystems, thus conservation tools
themselves should not negatively affect target species. Predator-exclusion cages are effectively used to reduce predation of
turtle nests; however, their effects on nest environment and developing hatchlings have not been examined.
Aims. Our study had the following four goals: (1) to examine effects of cages on the nest environment, (2) determine
whether nest caging affects proxies for hatchling tness, (3) evaluate whether nest predators preferentially interact with
certain cage types, and (4) assess the cost-effectiveness of different nest caging designs.
Methods. In 2010 and 2011 in Algonquin Provincial Park, Ontario, painted turtle (Chrysemys picta;n= 93) and snapping
turtle (Chelydra serpentina;n= 91) nests were assigned to one of three treatments (wooden-sided cages, above- and below-
ground wire cages) or a control (no nest cage) and outtted with a data logger to record incubation temperature. After
emergence, hatching success and proxies of hatchling tness were measured.
Key results. Nest temperature, hatching success, frequency of hatchling deformities and locomotor performance did not
differ among cage treatments. However, hatchling body condition differed among treatments; wooden-sided and below-
ground cages had the most positive inuence on body condition in painted and snapping turtles, respectively. Predator
interactions did not differ among treatments, and wooden-sided cages were the most inexpensive to construct.
Conclusions. Nest cages did not alter the nest environment from natural conditions but did alter hatchling body condition,
and nest caging affected species differently.
Implications. Nest cages are known to reduce nest depredation, and our data indicated that, in general, nest cages also do
not affect the nest environment or proxies for hatchling tness. Thus, our ndings indicated that cages are effective
conservation tools that do not present secondary deleterious effects on potential recruitment.
Received 16 May 2013, accepted 4 October 2013, published online 7 November 2013
An increasingly important priority in the eld of conservation
biology is the mitigation of human impacts on natural ecosystems.
Thus, conservation techniques themselves should not incur
negative, secondary impacts on target species (Frazer 1992).
A global threat to marine and freshwater turtles and tortoises is
increased nest predation as a result of subsidised predators.
Predators of turtle eggs (e.g. raccoons, skunks, foxes) increase
in abundance because of an increase in food resources associated
with human presence, which in turn causes nest predation to
occur at higher-than-natural levels (Christiansen and Gallaway
1984; Garber and Burger 1995; Mitchell and Klemens 2000;
Engeman et al.2003; Barton and Roth 2008; Kurz et al.2011;
Spotila 2011; Smith et al.2013). In addition, decreases in
populations of top predators in urban areas (e.g. wolves, large
cats) have increased the numbers of mesopredators, again leading
to increases in depredation of turtle eggs (Prugh et al.2009;
Ritchie and Johnson 2009). In some turtle populations, subsidised
mesopredators annually depredate 100% of nests, resulting in
chronic prevention of recruitment (Spinks et al.2003; Fordham
et al.2008). Substantial, repeated reductions in recruitment (e.g.
50% or more decrease in egg survival) have been found to
exacerbate population declines (Crouse et al.1987; Crowder
et al.1994; Heppel 1997; Tomillo et al.2008; Reed et al.2009).
The conservation tool used worldwide to eliminate nest predation
and promote recruitment is nest caging. Nest caging reduces nest
predation from as high as 100% depredation of nests without
cages to as low as 0% depredation of nests with cages (Addiston
1997; Ratnaswamy et al.1997; Yerli et al.1997; Gillingwater
2001; Engeman et al.2006; Kornaraki et al.2006; Kurz et al.
2011; Perez-Heydrich et al.2012; Smith et al.2013). This tool has
been in use since the 1960s (Breckenridge 1960), and specic
methods vary considerably among studies, many of which are
unpublished stewardship projects. Shortcomings of the technique
have been noted, namely, wire cages can entrap hatchlings
(Adamany et al.1997), wire cages alter the magnetic eld
Wildlife Research
Journal compilation CSIRO 2013
around the nest, which may affect sea turtle orientation and
navigation (Irwin et al.2004), and cages with materials above
ground level may alter the nest environment (e.g. shading which
would reduce incubation temperature; Breckenridge 1960;
Rahman and Burke 2010). Female turtles select nest sites on
the basis of environmental characteristics that maximise hatching
success (Wilson 1998; Refsnider and Janzen 2010). Evidence that
nest caging may alter those characteristics suggests that this
technique requires evaluation.
Nest environment (e.g. incubation temperature, soil moisture)
greatly inuences hatchling performance and morphology.
Reduced incubation temperature results in a decline in
hatching success (Correa-H et al.2010; Garrett et al.2010). In
northern temperate regions (e.g. Ontario, Canada), if incubation
temperatures are reduced, turtle embryos may not complete
development or emerge from the nest cavity before the onset
of cool fall temperatures (Yntema 1968; Choo and Chou 1987;
Bobyn and Brooks 1994; Du and Ji 2003). In addition, incubation
may be extended into a time period when habitat conditions are
unfavourable (Bobyn and Brooks 1994; Matsuzawa et al.
2002). Furthermore, embryos exposed to low temperatures
during incubation have reduced body condition, a higher
frequency of deformities and reduced locomotor performance
(Díaz-Paniagua et al.1997; Packard et al.1999; Hewavisenthi
and Parmenter 2001; Steyermark and Spotila 2001; Reece et al.
2002; Du and Ji 2003; Booth et al.2004). Many turtle species
exhibit temperature-dependent sex determination (TSD), and
altered nest temperatures could result in skewed sex ratios
(Schwarzkopf and Brooks 1985; Janzen and Paukstis 1991;
Hanson et al.1998; Wibbels 2003), in turn leading to reduced
population viability (Steen and Gibbs 2004). More broadly,
hatchling survival, growth rates, behaviours and habitat
selection have all been related to incubation temperature
(McKnight and Gutzke 1993;OSteen 1998; Rhen and Lang
1999;Booth et al.2004). In general, a substantial portion
of a turtles individual characteristics are determined by the
environment during embryogenesis.
The goal of the research presented here was to evaluate nest
caging types in terms of their impacts on nest environment,
proxies for hatchling tness, predator attraction and logistical
considerations. The following three types of nest cages currently
used in the recovery of at-risk turtles were evaluated: above- and
below-ground hardware cloth cages, and wooden-sided cages.
Data were also collected from natural nests (e.g. non-caged
control nests). The rst objective of the study was to compare
the effect different nest cage types may have on the environment
of the nest. We tested the hypothesis that if nest cage materials
block solar radiation, then temperature within the nest cavity
of above-ground and wooden-sided cages will be reduced. The
second objective was to determine the effect different nest cages
may have on hatching success, incubation duration, hatchling
body condition and performance. Following the prediction from
objective one, if temperature within the nest cavity is reduced,
this will have negative effects on nest success and hatchling
tness. We tested the prediction that above-ground and wooden-
sided cages would experience lower hatching success and longer
incubation durations. Also, we predicted that above-ground and
wooden-sided cages would have a negative effect on proxies of
hatchling tness, measured as a higher frequency of deformities
(Mast and Carr 1989; Türkozan et al.2001), reduced body
condition (Shine et al.2001) and reduced locomotor
performance (Freedberg et al.2004; Delmas et al.2007). Nest
predators may use research markers as visual cues for predation
(Burke et al.2005; Rollinson and Brooks 2007; Spotila
2011); thus, the third objective was to determine whether
predators preferentially interacted with, and depredated nests
with protective cages. If nest cages were used as visual cues,
then we predicted that predators would preferentially interact
with, and depredate above-ground and wooden-sided nest cages.
As conservation initiatives are often constrained by funding, the
nal objective of our study was to perform a cost analysis of each
nest cage type.
Study area
The study took place in Algonquin Provincial Park, Ontario,
Canada, near the Wildlife Research Station (WRS; 45350N,
78300W). Elevations on the western side of Algonquin Park
(370570 m above sea level) are higher than the surrounding
landscape and the area experiences a colder and wetter climate as a
result (Ontario Ministry of Natural Resources 1998). This climate
is reective of the northern range limits of both turtle species
studied. The study area is within the AlgonquinLake Nipissing
ecoregion, and is a rugged landscape underlain by Precambrian
Shield outcrops (Ontario Ministry of Natural Resources 1998).
Forest cover dominates, including predominantly mixed upland
forests of sugar maple (Acer saccharum), yellow birch (Betula
alleghaniensis) and eastern hemlock (Tsuga canadensis). Field
sampling was concentrated in two study sites, namely, WRS and
Arowhon. Nesting habitat in the WRS site varies from natural
sand dunes to gravel embankments along access roads and
Highway 60. The Arowhon site main nesting area is the sand
and gravel embankment of a public hiking trail (Schwarzkopf and
Brooks 1985).
Snapping and painted turtle populations are substantial at the
study sites, and nesting has been consistently documented over
the past 35+ years (R. J. Brooks, University of Guelph, unpubl.
data). By using these two relatively common species, we could
achieve large sample sizes and robust statistical analyses, leading
to ndings about nest caging applicable to turtle species-at-risk.
Examining two species with different nest characteristics,
namely, shallow nest with a small number of eggs (painted
turtles) vs deep nest with a large number of eggs (snapping
turtles), allowed us to capture variation among species.
Field methodology
Nest-site monitoring occurred from 20 May to 20 June 2010, and
5 June to 4 July 2011. Nest monitoring commenced when females
of either species started to congregate in aquatic habitats adjacent
to nest sites (i.e. staging), and/or terrestrial nest searching
behaviour was observed. Nest sites were monitored visually by
researchers from dawn (~0500 hours) to ~1000hours, and in the
afternoon from just before dusk (~1700 hours) until after dark, as
long as nesting activity was occurring. This timing captured
peak nesting for snapping and painted turtles (Ernst and
Lovich 2009). Nest monitoring ceased when 3 days elapsed
continuously without any observations of nesting activity.
BWildlife Research J. L. Riley and J. D. Litzgus
Nests were excavated after females completed oviposition
and covering of their nests. Nest locations were marked with
metal stakes and agging tape. Eggs were removed, and placed
in plastic bins lined with moistened vermiculite. As eggs were
removed, they were numbered using a pencil, to ensure that they
were returned to the nest cavity in the same order and orientation
as they were found. Depth to the top and bottom of the nest
cavity was measured to the nearest 0.1 cm by using a ruler.
After excavation, nest cavities were lled with soil removed
during egg retrieval, to reduce desiccation of the nest chamber.
Eggs were transported back to the WRS laboratory, where data
were collected for the long-term study. Eggs were returned to
the nest cavity within 24 h post-oviposition, before the vitteline
membrane adhered to the inner shell surface to form a white
spoton the egg (Yntema 1968; Rafferty and Reina 2012),
ensuring no trauma to developing embryos (Samson et al.2007).
Each nest was randomly assigned to one of the treatments
(Table 1). In 2010, there were two treatments, above- and below-
ground hardware cloth cages, and a control (no cage). In 2011, an
additional treatment, namely wooden-sided cages, was added.
The cages were all open-bottomed cubes. The above-ground cage
was made with 1-cm-mesh hardware cloth; dimensions were
30 30 40 cm, with 8-cm aps, and they were installed with
20 cm above and 20 cm below ground surface (Fig. 1; Addiston
1997; Irwin et al.2004). Below-ground cages were also made of
1-cm hardware cloth; dimensions were 30 30 20 cm and did
not have any aps, and they were installed so that the top of the
cage was just below ground level (Fig. 1; Hughes and Brooks
2006; Bolton et al.2008). The wooden-sided cages consisted of
a wooden square frame (made of boards 14 3.8 35 cm) with a
1-cm hardware-mesh top. The dimensions were 35 35 9 cm,
and the cages were installed over the top of the nest, with none of
the cage extending below the ground, and with either rocks or
stakes holding the cage securely against the soil (Fig. 1; Standing
et al.1999). Eggs were reburied in the original nest cavity, at
the original depths and order, with a temperature data logger in
the centre of the clutch. The temperature data loggers were
either a waterproofed iButton
(accuracy of 1C or 0.5C;
Thermochron DS1921G; Dallas Semiconductor, Sunnyvale,
CA, USA), or a HOBO StowAway
(accuracy of 0.2C;
TidbiT TBI32-05+37; Onset Computer Corporation, Bourne,
CA, USA). Temperature readings from data loggers of
different types and with and without waterproong did not
differ (F
= 2.01, P= 0.94; Roznik and Alford 2012). Data
loggers recorded temperature hourly. Cages were installed
immediately after egg reburial and data-logger deployment.
For the control nests, a second data logger was buried beside
the nest at the same depth as the logger within the nest cavity.
This was done so that if a control nest was depredated and the
in-nestdata logger was consumed or excavated by the predator,
incubation-temperature data would still be available. In late
August 2010 and 2011, close to the estimated date of
hatchling emergence (and after embryogenesis), above-ground
cages were installed on the control nests so that emerging
hatchlings could be collected for measurement and tness tests.
Nest environmental variables were measured for all cage
treatments. Vegetation cover was estimated by placing a 1-m
quadrat on the ground with the nest in the centre, and the
percentage of bare ground, herbaceous and woody plants, and
leaf litter were visually estimated (Wilson 1998). In 2010 and
2011, vegetation cover was sampled monthly and bi-weekly,
respectively, post-egg reburial until hatchling emergence.
Additionally, on 16 August 2011, soil moisture (%) was
measured at a depth of 10 cm within the area enclosed by the
nest cage, or for control nests, beside the stake marking the
nest site. Soil moisture was measured using a VG-METER-
200 (Vegetronix, Bluffdale, UT, USA).
In 2010 and 2011, predator interactions with nest cages
were recorded daily throughout nesting and hatching seasons.
Outside of those time periods in 2010, nests were surveyed
opportunistically. In 2011, nests were surveyed for predator
interactions once per week. A predator interactionwas
recorded when substrate was cleared away from the nest cage,
and/or the cage was dug up. After recording a predator interaction,
soil was replaced around the nest so that multiple interaction
events could be recorded. If a nest was found with the eggs dug up
and/or eaten, the nest was recorded as depredated. If tracks and
scat were discernible, the predator species was identied and
recorded. Additionally, four trail cameras (119456C; Bushnell
Corporation, Overland Park, KS, USA) were set up from 1 July to
1 October 2011 at four different locations to capture interactions
of predators with nest cages.
Daily monitoring of nests began just before the estimated
period of hatchling emergence. The emergence time for nests was
estimated using incubation durations reported in literature for
snapping (63104 days) and painted turtles (8999 days; Ernst
and Lovich 2009). The rst nests of both snapping and painted
turtles emerged on 25 August in 2010 and, in 2011, on 27 August
for painted turtles and 1 September for snapping turtles. Once a
nest emerged, all hatchlings and unhatched eggs were collected
and transported to the WRS laboratory for processing. Hatchling
carapace and plastron lengths were measured to the nearest
0.01 mm by using digital calipers (3148, Traceable Digital
Calipers, Control Co., Friendswood, TX, USA). Hatchling
mass was measured to the nearest 0.1 g by using a digital scale
(SP202, Scout Pro, Ohaus Corporation, Pine Brook, NJ, USA).
Any deformities (e.g. curly tails, additional scutes) were recorded.
Deformities were considered to be any deviation from the normal
body plan (Ernst and Lovich 2009) that did not appear to be
caused by injury (Davy and Murphy 2009).
Each hatchling underwent a righting test. Each hatchling was
placed on its carapace on a cloth-covered board (30 15 cm) and
Table 1. Number of nests per treatment and number of hatchlings per
treatment (in parentheses, italic font) sampled during the 2010 and 2011
eld seasons in Algonquin Park, Ontario, Canada
For the control treatment, the rst number before the comma represents the
number of nests sampled for both environmental and hatchling data, and
the number after the comma represents the number of nests sampled only for
environmental data
Treatment Chrysemys picta Chelydra serpentina
2010 2011 2010 2011
Control (no cage) 9, 5 (31) 12, 6 (43)8,6(193) 12, 3 (288)
Below-ground cage 12 (63)13(56)12(291)12(352)
Above-ground cage 12 (29)12(61)12(294)14(312)
Wooden-sided cage 12 (66)12 (272)
Total 38 (123)55(226)38(778)53(1224)
Effects of predator-exclusion cages on turtle nests Wildlife Research C
attempts to ip over onto its plastron were observed for 15 min.
The following two variables were timed to the nearest 0.01 s by
using a digital stopwatch: (1) latency period (LP), the time from
placement on carapace until the rst righting attempt; and
(2) righting period (RP), the time from the rst righting
attempt until successful righting (Freedberg et al.2004;
Delmas et al.2007; Rasmussen and Litzgus 2010). Each trial
was recorded with a digital camera (Photosmart R742, Hewlett-
Packard Development Co., Mississauga, ON, USA), and LP
and RP were conrmed from the recordings. The number of
hatchlings that failed to right themselves within 15 min was
compared among treatments; these hatchlings were removed
from the comparison of RP among treatments. A turtle that
cannot quickly right itself is more likely to be depredated, or
to succumb to desiccation and drowning (Finkler and Claussen
1997). Thus, performance in righting tests is thought to reect a
hatchlings future survival, and therefore was used as a proxy
for tness (Freedberg et al.2004; Delmas et al.2007). After data
collection, hatchlings were released at their nests within 24 h. The
unhatched eggs were candled to assess fertility (Yntema 1964).
Emergence ceased on 30 September 2010 and 28 September
2011. Once daily mean air temperature dropped below 5C for
three consecutive days, any remaining nests were dug up to assess
hatching success. In 2010, unemerged nests were dug up from 1 to
4 October, and in 2011 from 2 to 7 October. Any hatchlings were
processed as described above.
We undertook a cost analysis of each caging design. First, we
calculated the monetary cost of equipment for each design, and
second, we calculated the effort (salary cost) to make and install
each cage by a technician. Time (to nearest min) was recorded
as technicians constructed and installed cages. The times for all
actions were then averaged, and multiplied by the technicians
salary cost (CAN$10.25 per h, the minimum wage in Ontario,
Canada) to estimate the effort per cage design.
Nest environmental variables, except temperature, were averaged
for each treatment. Because these data were non-normal, mean
soil moisture and vegetation cover were compared among
Fig. 1. Three nest-cage types were tested. In 2010, nests were randomly assigned to (a) below-ground
cages, (b) above-ground cages (shown before and post-installation from left to right), or (d) uncaged
nests (controls). In 2011, the 2010 treatments were repeated with the addition of (c) wooden-sided nest
DWildlife Research J. L. Riley and J. D. Litzgus
treatments separately for each turtle species, using a non-
parametric KruskalWallis ANOVA test. Depth to the bottom
of the nest cavity was compared between species using an
The temperature data were extracted from data loggers, and
data from in-nestdata loggers were preferentially used for the
control treatments. No difference was found in temperature
between in-nestand out-of-nestdata loggers (2011 data:
= 2.02, P= 0.89), so the out-of-nesttemperature data were
used when a control nest was predated.
Temperature data were analysed three ways. (1) Mean nest
temperature from the date of the last nest reburied to the rst
nest emerged (a 44- and 57-day period in 2010 and 2011,
respectively), and daily temperature variance during this time
period, were calculated for each nest. Mean daily temperature
variance describes daily temperature uctuations above and
below mean nest temperature (Paitz et al.2010; Neuwald and
Valenzuela 2011), and is known to affect hatchling development
(Schwarzkopf and Brooks 1985; Doody 1999; Ashmore and
Janzen 2003; Du and Ji 2003; Mullins and Janzen 2006; Les
et al.2007; Paitz et al.2010). (2) Mean temperature for each
third of incubation (Packard and Packard 1998), and daily mean
temperature and mean temperature variance for the second third
of incubation, the time period when sex is determined (Mahmoud
et al.1973; Yntema 1979; Bull and Vogt 1981; Bull 1985; Paitz
et al.2010; Neuwald and Valenzuela 2011), were calculated.
(3) Heat units (degree days, D) were calculated for each nest
by using the hourly trapezoid method (Holt 2000). Degree days
represent the number of heat units over a 24-h period above a
threshold temperature (T
). Below T
, no development occurs,
but above it, heat units stimulate development (Holt 2000). The
threshold temperature is 14C for painted turtles (Les et al.
2007), and 20C for snapping turtles (Holt 2000). We used
hourly temperatures to capture uctuations in temperature that
affect development. The hourly trapezoid method uses hourly
temperatures (T
,... T
) to calculate heat units (HU)
above a threshold temperature (T
HU ¼ ½ððT0þT1Þ=2ÞþððT1þT2Þ=2Þ
þþððT22 þT23Þ=2Þ=ð24 ToÞ
Temperature, temperature variance, temperatures for each
third of incubation, and heat units were compared among
treatments using ANOVAs that also included the additional
factors of species and year as necessary.
Hatching success (%) for each nest was calculated as the
number of live hatchlings divided by the number of eggs laid.
Hatching success was compared among treatments, species
and years by using a KruskalWallis ANOVA. Incubation
duration was the number of days between oviposition and
hatchling emergence for each nest and was compared among
treatments using an ANOVA that included the additional factors
of species and year. Deformities were quantied as the proportion
of deformed turtles out of the number of hatchlings in a clutch
(Davy and Murphy 2009). Proportion of deformed turtles in
each clutch was transformed using an arcsine-square-root
transformation to ensure normality (Gotelli and Ellison 2004).
Mean number of deformities per turtle in each clutch was also
calculated (de Solla et al.2008). To control for the random effect
of mothers identity, a linear mixed-effects model (LMEM) using
a restricted maximum likelihood estimation of variance was used
to examine whether deformities (proportion of hatchlings with
deformities in each clutch, and mean number of deformities per
hatchling per clutch) varied among treatments. In this model,
additional xed factors of species and year were included. Body
condition was tested separately for each species using a LMEM to
compare mass against the xed effects of treatment and carapace
length, and the random effect of clutch nested in mothers identity
(García-Berthou 2001; Litzgus et al.2008; Rasmussen and
Litzgus 2010). The number of hatchlings that failed to right
themselves within 15 min was compared among treatments
using a Pearsons Chi-squared test of association. Performance
variables (LP and RP) were transformed using log (y+ 1) to ensure
normality. LP and RP were tested separately for each species
among treatments using a LMEM that included the xed effect of
processing temperature (room temperature during righting tests),
which is linearly related to ectotherm performance (Hutchison
et al.1966), and the random effect of clutch nested in mothers
identity (to control for genetic effects).
Pearsons Chi-squared tests of association were used to test
whether count data from predation interactions and depredation
events differed among treatments. A one-way ANOVA was used
to test whether installation time (s) differed among treatments.
In all statistical tests, assumptions of normality and
heterogeneity of variance were veried. Measures were
transformed for normality as needed. An a posteriori Tukey
HSD test, which adjusted for multiple comparisons, was used
to identify differences among sample means when signicant
differences were found among treatments (Logan 2010). If a
signicant interaction was found in models with multiple xed
factors, it was reported, and if no signicant interaction was
found, only main effects were tested and reported. All summary
data are reported as the mean 1 standard error. The signicance
level of a=0.05 was used for all statistical tests. Statistical
analyses were performed using R (R Foundation for Statistical
Computing, Vienna, Austria).
Nest environment
Mean soil moisture (%) in the nests of painted and snapping
turtles did not differ among treatments (Table 2). For painted
turtle nests, percentage bare ground, leaf litter and herbaceous
plants did not differ among treatments (Table 2). Mean percentage
woody plants differed among treatments; nests with wooden-
sided cages had a greater percentage of woody plants than did
those in other treatments (Table 2). None of the vegetation
characters differed among treatments for snapping turtle nests
(Table 2). Nest depth differed between species (F
= 726.1,
P<0.01); snapping turtles had deeper nests (20.7 0.4 cm) than
painted turtles (9.6 0.1 cm).
Nest thermal environment
Mean incubation temperature (C) did not differ among cage
treatments (F
= 1.05, P= 0.37) or between species
= 0.01, P= 0.91), but differed between years
= 22.17, P<0.01; Tables 3,4). Mean daily temperature
variance in nests of painted turtles varied more than in those of
Effects of predator-exclusion cages on turtle nests Wildlife Research E
snapping turtles (F
= 203.93, P<0.01; Tables 3,4). Mean
daily temperature variance did not differ among treatments for
painted turtles (F
= 1.42, P= 0.24; Table 3), but did differ
among treatments for snapping turtles (F
= 3.42, P= 0.02;
Table 4). Snapping turtle nests with wooden-sided cages
experienced less variation than did nests with below-ground
cages (P= 0.02 for the comparison between wooden-sided and
below-ground cages, P>0.05 for all other cases; Table 4).
Mean temperature in each third of incubation did not differ
among treatments (F
= 1.09, P= 0.36; F
= 1.98, P= 0.13;
= 2.36, P= 0.08, respectively), or between species
= 1.82, P= 0.18; F
= 0.01, P= 0.94; F
= 0.78,
P= 0.38, respectively), but differed between years
= 39.14, P<0.01; F
= 13.99, P<0.01; F
= 18.17,
P<0.01, respectively; Tables 3,4).
In the second third of incubation, mean daily temperature
did not differ among treatments (F
= 2.09, P= 0.11) or
between species (F
= 0.003, P= 0.95), but differed
between years (F
= 12.76, P<0.01; Tables 3,4). For the
same period, mean daily temperature variance did not differ
among treatments (F
= 1.30, P= 0.28) or between years
= 1.70, P= 0.20), but differed between species
= 300.45, P<0.01); mean daily temperature variance
was greatest in painted turtle nests (Tables 3,4).
Heat units (D) were tested separately for each species,
because the threshold temperature differs between them. Mean
heat units did not differ among treatments or between years
for painted turtles (F
= 0.51, P= 0.68; F
= 0.15, P= 0.71,
respectively; Table 3) or snapping turtles (F
= 0.66, P= 0.58;
= 2.36, P= 0.13, respectively; Table 4).
Clutch and hatchling characteristics
Mean incubation duration did not differ among treatments
= 0.44, P= 0.73), or between species (F
= 0.74,
P= 0.39), but it was shorter in 2011 than in 2010 (F
= 4.27,
P= 0.04; Tables 5,6). Hatching success did not differ among
treatments in painted (H
= 5.25, P= 0.15; Table 5) or snapping
turtles (H
= 2.93, P= 0.40; Table 6).
Mean proportion of deformed turtles in each clutch did not
differ among treatments (F
= 1.56, P= 0.20), between species
= 0.28, P= 0.60) or between years (F
= 2.25, P= 0.14;
Tables 5,6). Mean number of deformities per hatchling in each
clutch also did not differ among treatments (F
= 2.56,
P= 0.06) or between species (F
= 3.15, P= 0.08), but there
were on average more deformities per hatchling in 2011 than in
2010 (F
= 5.11, P= 0.03; Tables 5,6).
Body condition of painted turtles differed among treatments
= 3.09, P= 0.03). Mass was greater at all carapace lengths
measured for hatchlings from wooden-sided cages. For body
condition of snapping turtles, a signicant interaction was found
between treatment and carapace length (F
= 107.09,
P<0.01). Mass was slightly greater at all carapace lengths
measured for hatchlings from below-ground cages than that for
those from the control and above-ground cages. Hatchlings from
above-ground cages had the lowest mass at carapace lengths less
than 27 mm. At carapace lengths less than ~28 mm, hatchlings
from wooden-sided cages had the greatest mass, but at carapace
lengths greater than ~28 mm, they had the lowest masses.
Table 2. Summary of soil moisture and vegetation types quantied in 1-m
quadrats centred on turtle nests in four nest-caging treatments
Data are means s.e. (%). Number of nests (n) is provided for each treatment. Test statistics from the KruskalWallis ANOVA test (H), degrees of freedom, and P-values are given for each nest characteristic.
Signicant test results are indicated in bold font. Data were analysed separately for each species to determine whether nest-environment characteristics differed among nest-cage treatments
Nest-environment Chrysemys picta Chelydra serpentina
characteristics Above-
ground cages
(n= 24)
ground cages
(n= 24)
sided cages
(n= 12)
No cage
(n= 31)
Test statistics Above-
ground cages
(n= 25)
ground cages
(n= 24)
sided cages
(n= 12)
No cage
(n= 29)
Test statistics
Soil moisture 9.2 ± 1.0 6.1 ± 0.5 6.7± 0.8 8.5 ± 1.1 H
= 7.04, P= 0.07 5.3 ± 0.6 6.9 ± 1.0 6.4± 1.5 8.1 ± 1.8 H
= 3.35, P= 0.34
Bare ground 77.1 ± 2.4 81.1 ± 3.3 67.9 ± 5.2 70.5 ± 3.3 H
= 7.74, P= 0.06 87.9 ± 2.7 86.3 ± 2.4 89.2 ± 2.6 84.0 ± 2.6 H
= 1.13, P= 0.77
Herbaceous plants 13.2 ± 1.9 12.2 ± 2.6 13.6 ± 3.7 17.8 ± 2.6 H
= 2.93, P= 0.40 7.5 ± 1.5 7.8 ± 1.7 6.1± 1.8 12.6 ± 2.3 H
= 0.43, P= 0.94
Woody plants 6.5 ± 1.3 3.6 ± 0.9 13.6± 3.7 7.0 ± 1.4 H
= 8.24, P= 0.04 1.3 ± 0.6 1.8± 0.7 3.2 ± 1.9 1.3 ± 0.5 H
= 1.50, P= 0.68
Leaf litter 3.2 ± 0.5 3.1 ± 0.9 6.8± 2.2 4.3 ± 0.8 H
= 5.74, P= 0.13 3.3 ± 1.7 4.0 ± 1.8 1.6± 0.5 2.1 ± 0.6 H
= 3.37, P= 0.34
FWildlife Research J. L. Riley and J. D. Litzgus
The number of hatchlings that failed to right themselves in
15 min did not differ among treatments for painted (c
= 0.52,
P= 0.92; Table 5) or snapping turtles (c
= 3.60, P= 0.31;
Table 6). LP and RP of painted turtles did not differ among
treatments (F
= 1.79, P= 0.15; F
= 0.17, P= 0.92;
Table 5), and LP and RP of snapping turtles did not differ
among treatments (F
= 1.81, P= 0.14; F
= 2.08,
P= 0.10; Table 6). A signicant interaction between treatment
and processing temperature was found for snapping turtle RP
= 2.93, P= 0.03). Hatchlings from above-ground cages
had the slowest RP across all processing temperatures. The slope
of RP versus processing temperature was similar for the wooden-
sided and control treatment; over most processing temperatures,
hatchlings from wooden-sided and control nests had the fastest
RP. However, RP did not vary by more than half a second between
any treatments.
Predators and nest cages
Over the course of incubation, the number of predator interactions
with above-ground cages was 14, with below-ground cages 16,
and with wooden-sided cages it was 2. The number of caged
nests with which predators interacted did not differ among
treatments (c
= 0.06, P= 0.97). The number of successful
depredation events was 3, 1 and 3 for above-ground, below-
ground and wooden-sided cages, respectively. The number of
Table 3. Summary of Chrysemys picta nest-temperature data
Data are means s.e. and sample sizes (n= number of nests) are given in parentheses
Temperature variable Nest-cage treatment
Above-ground cages Below-ground cages Wooden-sided cages Control (no cage)
2010 2011 2010 2011 2010 2011 2010 2011
Summer hourly temperature (C) 23.8 ± 0.15
(n= 11)
24.8 ± 0.26
23.7 ± 0.45
25.3 ± 0.25
24.4 ± 0.31
(n= 12)
23.9 ± 0.24
(n= 14)
24.3 ± 0.30
(n= 16)
Heat units (D) 803.4
815.8 ± 0.5
819.6 ± 0.3
781.8 ± 0.6
849.6 ± 0.3
812.9 ± 0.02
Temperature variance (C) 15.0 ± 3.1
(n= 11)
15.7 ± 1.6
15.6 ± 2.0
19.2 ± 1.2
15.0 ± 1.9
(n= 12)
15.9 ± 1.5
(n= 14)
20.8 ± 1.5
(n= 16)
First third of incubation
hourly temperature (C)
22.7 ± 0.9
22.2 ± 0.5
22.5 ± 0.6
21.9 ± 0.2
22.2 ± 0.2
Second third of incubation
hourly temperature (C)
25.7 ± 0.6
27.5 ± 0.5
25.4 ± 0.7
24.8 ± 0.3
25.4 ± 0.06
Final third of incubation
hourly temperature (C)
21.0 ± 0.6
22.5 ± 0.02
20.4 ± 1.1
22.8 ± 0.3
20.2 ± 0.3
Second third of incubation
daily temperature (C)
25.7 ± 0.6
27.5 ± 0.5
25.4 ± 0.7
24.8 ± 0.3
25.4 ± 0.06
Second third of incubation
temperature variance (C)
20.4 ± 2.1
21.1 ± 5.4
20.39 ± 3.8
19.0 ± 2.9
19.9 ± 2.4
Table 4. Summary of Chelydra serpentina nest temperature data
Data are means s.e. and sample sizes (n= number of nests) are given in parentheses
Temperature variable Nest-cage treatment
Above-ground cages Below-ground cages Wooden-sided cages Control (no cage)
2010 2011 2010 2011 2010 2011 2010 2011
Summer hourly temperature (C) 23.5 ± 0.3
(n= 12)
24.7 ± 0.4
24.1 ± 0.2
(n= 11)
25.0 ± 0.3
(n= 10)
24.2 ± 0.4
(n= 11)
24.2 ± 0.2
(n= 14)
24.5 ± 0.3
(n= 14)
Heat units (D) 291.2 ± 0.2
322.1 ± 0.3
296.6 ± 0.2
326.6 ± 0.3
(n= 10)
310.5 ± 0.3
284.2 ± 0.1
292.0 ± 0.3
(n= 10)
Temperature variance (C) 4.1 ± 0.4
(n= 12)
4.6 ± 0.6
6.3 ± 1.7
(n= 11)
6.7 ± 1.0
(n= 10)
3.1 ± 0.5
(n= 11)
6.0 ± 1.0
(n= 14)
5.1 ± 0.7
(n= 14)
First third of incubation
hourly temperature (C)
21.5 ± 0.4
23.0 ± 0.3
21.1 ± 0.2
23.1 ± 0.2
(n= 10)
22.9 ± 0.4
21.8 ± 0.4
23.0 ± 0.3
(n= 10)
Second third of incubation
hourly temperature (C)
24.6 ± 0.2
26.4 ± 0.5
25.0 ± 0.3
26.3 ± 0.5
(n= 10)
26.1 ± 0.4
24.6 ± 0.2
25.3 ± 0.6
(n= 10)
Final third of incubation
hourly temperature (C)
22.4 ± 0.6
21.4 ± 0.6
23.1 ± 0.3
20.9 ± 0.5
(n= 10)
21.1 ± 0.5
21.3 ± 0.6
20.2 ± 0.7
(n= 10)
Second third of incubation
daily temperature (C)
24.6 ± 0.2
26.4 ± 0.5
25.1 ± 0.4
26.3 ± 0.5
(n= 10)
26.1 ± 0.4
24.6 ± 0.2
25.3 ± 0.6
(n= 10)
Second third of incubation
temperature variance (C)
4.1 ± 0.6
4.7 ± 0.4
4.4 ± 1.0
6.7 ± 2.7
2.7 ± 0.5
3.4 ± 0.4
4.6 ± 0.7
(n= 10)
Effects of predator-exclusion cages on turtle nests Wildlife Research G
nests successfully depredated did not differ among treatments
= 0.22, P=0.90). The number of nests successfully
depredated after being interacted with by a predator one or
more times was 1 for above-ground cages, 0 for below-ground
cages, and 1 for wooden-sided cages.
Images of predators investigating the nest cages (either
snifng or looking at the cage) were captured 23 times by the
trail cameras, and included Vulpes vulpes,Canis lycaon and
Corvus corax. Predators interacting with nest cages (e.g.
digging) were captured 18 times by the cameras and included
V. vulpes and C. lycaon; these interactions were veried by visual
inspections of the nests.
Cost analysis of nest-cage designs
Wooden-sided cages were made of the least expensive materials,
and above-ground cages required the most expensive materials
(Table 7). Construction time was shortest for wooden-sided cages
and longest for above-ground cages (Table 7). Installation time
did not differ among cage types (F
= 2.11, P= 0.14;
Table 5. Summary of Chrysemys picta clutch and hatchling data
Data are means s.e. For the rst four variables (14), samples size (n) represents the number of nests, and for the last three variables (57), nrepresents the number
of hatchlings. If data were analysed between years, means are shown separated by commas, and in some instances, year data were pooled. LP, latency period; RP,
righting period
Clutch and hatchling variable Nest-cage treatment
Above-ground cages Below-ground cages Wooden-sided cages Control (no cage)
(1) Incubation duration (days) 97.0, n= 1 (2010);
89.3 ± 4.5, n= 4 (2011)
83.5 ± 3.5, n= 2 (2011)
94.0 ± 5.8, n= 4 (2011)
94.2 ± 3.4, n= 6 (2010);
97.3 ± 3.1, n= 3 (2011)
(2) Hatching success (%) 69.3 ± 8.0, n= 24 79.1 ± 6.7, n= 25 76.4 ± 4.4, n= 12 59.7 ± 8.8, n=20
(3) Proportion of deformed
hatchlings per clutch
0.23 ± 0.1, n= 6 (2010);
0.18 ± 0.06, n= 10 (2011)
0.41 ± 0.11, n= 10 (2010);
0.30 ± 0.08, n= 10 (2011)
0.36 ± 0.06, n= 12 (2011)
0.37 ± 0.12, n= 8 (2010);
0.33 ± 0.05, n= 9 (2011)
(4) Number of deformities
per turtle per clutch
0.30 ± 0.12, n= 6 (2010);
0.38 ± 0.14, n= 10 (2011)
1.23 ± 0.41, n= 10 (2010);
0.55 ± 0.2, n= 10 (2011)
0.63 ± 0.1, n= 12 (2011)
0.73 ± 0.27, n= 8 (2010);
0.59 ± 0.12, n= 9 (2011)
(5) Number of hatchlings
that failed to right
3, n=91 5, n= 115 3, n=63 9,n=77
(6) LP (s) 73.9 ± 11.6, n= 86 126.0± 13.9, n= 114 106.0 ± 17.6, n= 62 128.6 ± 17.1, n=70
(7) RP (s) 11.6 ± 4.1, n= 86 23.1 ± 8.0, n= 114 11.0 ± 5.1, n= 62 12.4 ± 4.0, n=70
Table 6. Summary of Chelydra serpentina clutch and hatchling data
Data are means s.e. For the rst four variables (14), samples size (n) represents the number of nests, and for the last three variables (57), nrepresents the number
of hatchlings. If data were analysed between years, means are shown separated by commas, and in some instances, year data were pooled. LP, latency period; RP,
righting period
Clutch and hatchling variable Nest-cage treatment
Above-ground cages Below-ground cages Wooden-sided cages Control (no cage)
(1) Incubation duration (days) 93 ± 2.2, n= 10 (2010);
88.1 ± 3.0, n= 10 (2011)
92.7 ± 1.8, n= 9 (2010);
89.8 ± 1.9, n= 12 (2011)
89.4 ± 2.0, n= 8 (2011)
93.4 ± 2.7, n= 7 (2010);
89.8 ± 2.7, n= 11 (2011)
(2) Hatching success (%) 82.2 ± 6.9, n= 23 85.2 ± 4.2, n= 21 73.2 ± 12.0, n= 10 73.0 ± 7.0, n=20
(3) Proportion of deformed
hatchlings per clutch
0.27 ± 0.06, n= 10 (2010);
0.24 ± 0.07, n= 10 (2011)
0.36 ± 0.06, n= 11 (2010);
0.28 ± 0.06, n= 12 (2011)
0.25 ± 0.07, n= 8 (2011)
0.28 ± 0.08, n= 8 (2010);
0.14 ± 0.04, n= 11 (2011)
(4) Number of deformities per
turtle per clutch
0.47 ± 0.12, n= 10 (2010);
0.41 ± 0.14, n= 10 (2011)
0.72 ± 0.2, n= 11 (2010);
0.53 ± 0.2, n= 12 (2011)
0.41 ± 0.1, n= 9 (2011)
0.54 ± 0.2, n= 8 (2010);
0.19 ± 0.06, n=11 (2011)
(5) Number of hatchlings
that failed to right
53, n= 599 42, n= 643 21, n= 271 19, n= 481
(6) LP (s) 75.2 ± 6.0, n= 546 67.1 ± 5.1, n= 634 108.3 ± 9.6, n= 250 93.7 ± 7.1, n= 429
(7) RP (s) 3.9 ± 0.9, n= 546 6.7 ± 1.9, n= 634 5.5 ± 1.8, n= 250 11.6 ± 2.8, n= 429
Table 7. Summary of the cost analysis for each nest cage design
The costs shown are per single nest cage. Salary cost was CAN$10.25/h, the minimum wage in Ontario, Canada
Nest-cage type Material
cost ($)
time (min)
time (min)
time (min)
cost (CAN$)
cost (CAN$)
Wooden-sided cages 2.20 15 (n= 25) 6 (n= 7) 21 3.60 5.80
Below-ground cages 4.90 82 (n=5) 13 (n= 14) 95 16.20 21.10
Above-ground cages 9.10 100 (n= 15) 10 (n= 7) 110 18.80 27.90
HWildlife Research J. L. Riley and J. D. Litzgus
Table 7). The total cost, including materials and salary, was
lowest for wooden-sided cages (Table 7).
Nest environment
Most environmental characteristics did not differ among nest-
cage types. Around painted turtle nests with wooden-sided cages,
the percentage of woody plants was greater than that in all other
treatments. Installing wooden-sided cages did not involve
digging through plant roots, whereas installation of the other
cages involved digging 20 cm below ground through plant roots.
Thus, differences in cage-installation requirements may alter the
vegetation around the nest from what was maternally selected.
Most thermal-environment characteristics did not differ
among treatments, which did not support our prediction that
nest-cage materials would shade and reduce the temperature
within the nest. Nest temperature, temperature during each
third of embryo development, and heat units did not differ
among treatments. Daily temperature variance in snapping
turtle nests was lower in the wooden-sided than below-ground
cage treatment, but not different among any other treatments
for snapping or painted turtles. Wooden-sided cages appear
to reduce temperature uctuations in snapping turtle nests.
Overall, the thermal environment of the nest was not altered
greatly from natural conditions by any of the nest-cage types.
These ndings indicated that nest cages preserve most of the
thermal characteristics that females select to maximise hatching
success, and turtle researchers who use above- and below-ground
nest cages in their studies are recording temperature data
reective of natural conditions.
None of the nest-cage types tested in our study altered
temperature from natural conditions during the TSD thermo-
sensitive period. During the thermo-sensitive period, painted
turtle embryos across all treatments were incubated at a mean
of 25C, with a daily temperature variance of 20C. According
to the variable degree model of TSD in painted turtles, if
development in the thermo-sensitive period occurs between
22C and 28C, then that clutch will be entirely male (Bull and
Vogt 1981; Neuwald and Valenzuela 2011). However, both
male and female painted turtles occur at our study site, which
may be attributable to temperature uctuations during the thermo-
sensitive period having a feminising effect on the embryos (Les
et al.2007; Paitz et al.2010; Neuwald and Valenzuela 2011), or
as a result of prior higher annual temperatures. Snapping turtles
across all treatments were incubated at a mean of 26C, with a
daily temperature variance of 5C; this mean temperature is
known to result in development of males (Wilhoft et al.1983),
but does not account for an effect of thermal variance, which has
also been found to affect sex ratio in C. serpentina (Freedberg
et al.2011). In recent years, conservation concerns have grown
over road mortality of females that results in male-biased
populations, and global warming which also may skew sex
ratios (Mrosovsky and Provancha 1989; Steen and Gibbs
2004; Hawkes et al.2007). As cages were not found to alter
nest temperature, wildlife managers could not use nest cages to
promote equal sex ratios in turtle populations where sex ratio is
skewed. More importantly, nest caging does not appear to alter
nest temperatures in a way that will affect TSD in turtles.
Clutch and hatchling characteristics
Incubation duration did not differ among treatments, which was
expected because incubation duration is inversely related to
incubation temperature and there were no differences in
temperature among cage treatments. In central Ontario, near
the northern range limits of turtles, this is critical knowledge
as conservation strategies must take into account a short active
season. Nest cages did not extend incubation into colder months
that could prevent development, and/or force over-wintering
within the nest (Bobyn and Brooks 1994). Also, nest cages did
not alter hatching success from natural levels. Thus, nest cages
are a conservation tool that maintains natural levels of hatching
success within the natural emergence period, while in turn
increasing the amount of nest success by protecting nests from
Some proxies of hatchling tness did not differ among
treatments. Deformity rates and locomotor performance (LP
and RP) did not differ among treatments, which is not
surprising because incubation temperature affects both of these
proxies (McKnight and Gutzke 1993; Díaz-Paniagua et al.1997;
Hewavisenthi and Parmenter 2001; Steyermark and Spotila
2001) and we found no differences in temperature among cage
treatments. Hatchling body condition, another proxy for tness,
varied among treatments and the effects of cages on body
condition were not consistent between species. For painted
turtles, wooden-sided cages, and for snapping turtles, below-
ground cages had positive effects on body condition. Above-
ground cages negatively affected body condition of snapping
turtles. Species-specic differences may be due to differences in
nest environment. Nest-site preferences differ between painted
and snapping turtles (Schwarzkopf and Brooks 1987; Weisrock
and Janzen 1999; Kolbe and Janzen 2002; Hughes and Brooks
2006). We found that the amount of woody plants around nests
was different among treatments in painted turtles but not
snapping turtles. Also, nest-temperature variance was much
greater in the nests of painted turtles than in the nests of
snapping turtles, which may relate to the fact that snapping
turtles lay nests about two times deeper than do painted turtles
(Ernst and Lovich 2009); the greater depth buffers the nest from
temperature uctuations (Spotila 2011). The differences found
between species highlighted the importance of a multi-species
approach to the evaluation of conservation techniques. Additional
species-specic evaluation of this conservation tool is necessary
for species with nest characteristics that differ greatly from the
species studied here (e.g. sea turtles; Spotila 2011).
Differences in body condition among treatments did not
appear to be driven by the hypothesised mechanism (shading
by cage material) because incubation temperature did not differ
among treatments. In contrast to our predictions, hatchlings
incubated in wooden-sided and above-ground cages (the cages
with the potential for shading) did not have the poorest body
conditions. So, what is the mechanism behind the differences
found? Temperature variance differed signicantly among
treatments in snapping turtles. Nests with below-ground cages
had the most variable temperatures of all the treatments (Table 4)
and produced hatchlings that were heavier across all carapace
lengths. Painted turtles incubated in wooden-sided cages were
heavier than hatchlings at the same carapace length in other
Effects of predator-exclusion cages on turtle nests Wildlife Research I
treatments, and even though a difference was not found among
treatments, nest temperature was less variable than in the other
treatments (Table 3). Perhaps temperature variation, and in turn
hatchling body condition, are affected by nest-cage type, and
the effect differs between species. Shallow painted turtle nests
experience more temperature variance, so reducing the variance
by using wooden-sided cages may be benecial, whereas in
snapping turtles, increasing the variance is not harmful (and
may even be benecial) because they generally experience low
variance in their deep nests. It would appear that a moderate
amount of temperature variance (~10C) may improve body
condition, and this is achieved by lowering variance in painted
turtle nests and increasing variance in snapping turtle nests.
Furthermore, temperature variation inuences the development
of turtles and has been found to affect body size, locomotor
performance and growth in various species (Doody 1999;
Ashmore and Janzen 2003; Du and Ji 2003; Booth 2006; Les
et al.2007; J. L. Riley, S. Freedberg and J. D. Litzgus 2013,
unpubl. data). Alternatively, other measures of nest environment
that were not measured in our study may have been affected by
nest-cage type, and may have driven the differences in hatchling
body condition among cage types. Overall, more research is
needed to uncover the mechanism driving the differences in
hatchling body condition among treatments.
Predators and nest cages
Predator interactions with nest cages and successful depredation
events did not differ among nest-cage types. This indicates that
predators are not attracted to one nest-cage type over another, and
that all nest-caging types are equivalent in protecting turtle nests.
Similarly, Burke et al.(2005) and Strickland et al.(2010) found
that marking nests did not increase raccoon depredation rates.
Additionally, Kurz et al.(2011) found that an enlarged version of
the above-ground cage in our study did not attract foxes over
other, less conspicuous, cage types. In contrast, Mroziak et al.
(2000) found that nest caging may cue raccoons to the presence
of a nest and attract depredation attempts. In an 8-year study,
Rollinson and Brooks (2007) found that Corvus sp. used nest
markers as visual cues of nests. Within a short-term study period
(2 years), nest cages or nest ags are not likely to be a learnedcue
for nest predators; however, over the long term, certain predator
species may learn to associate nest markers with a food source.
In our study, above-ground and wooden-sided cages both had
instances where after repeated predator interactions, the nest was
successfully depredated. Cages, such as these, that extend above
ground level may attract multiple predation interactions, which
increase both the probability of nest predation, and opportunities
to learn that nest cages cue a food source. It is also important to
note that our study was conducted in an area where predation
pressures were relatively low. In areas where subsidised predators
are abundant, or where burrowing predators (like snakes and
rodents) are present, cages that extend underground around the
nest cavity may be desirable (Rodríguez-Robles 1998; Converse
et al.2002; Plummer 2010).
Cost analysis of nest-cage designs
Often, the biggest constraint for conservation actions is funding.
Our cost analysis showed that wooden-sided cages were the most
cost-effective design. Wooden-sided cages are also simple for
volunteers to construct (Mersey Tobeatic Research Institute and
Parks Canada 2009). However, there are other factors to consider.
For instance, nest caging that extends above the ground
(potentially paired with an educational sign) could be used to
increase public awareness of the threats facing turtle populations
(Newbury et al.2002). At study sites in Algonquin Park, many
park visitors took interest in our nest cages. Signs were posted
around the study sites, which often prompted the public to engage
in discussions regarding actions an individual could take to
restore turtle populations. But, if other concerns are driving
decisions about nest caging, for example maximising crypsis
of nest cages in areas where disturbance from the public is
prevalent (Bolton et al.2008), or if threats of poaching exist,
then other nest-caging types, such as below-ground cages, should
be employed. The highest priority in a management program
should be to maximise nest success and hatchling tness, but it
is understandable that wildlife managers need to also consider
logistical, funding and goal-based concerns when choosing a
nest-cage type for conservation programs.
Overall, nest cages did not substantially alter the nest environment
from natural conditions. Above-ground cages negatively affected
body condition in one species, but the other cage types did not
negatively affect hatchling tness, indicating that they are
effective conservation tools that do not present secondary
deleterious effects on potential recruitment. In conservation of
long-lived species, such as turtles, it is important to pay attention
to indicators of survival in early life stages because it is difcult
to see the population-level outcomes of recovery actions for
decades, which delays evaluation and adaptive management
(Spencer and Janzen 2010). The effects of nest-cage types on
hatchling body condition differed between species, perhaps due
to differences in nest depth and thermal regimes. Selection of a
nest-cage type for conservation strategies should be based on
maximising nest success, hatchling tness, and on logistical
concerns (e.g. ease and efciency of construction, installation
and material costs). Our evaluation of nest caging provides
essential knowledge to researchers, wildlife managers, and
conservationists for use globally in at-risk turtle-management
strategies and research.
Financial support was provided by Natural Sciences and Engineering
Research Council (NSERC; CGS-M scholarship to JLR and Discovery
Grant to JDL), Canadian Wildlife Federation, Ontario Ministry of Natural
Resources (OMNR), Toronto Zoo, and Laurentian University. In-kind
contributions were provided by Algonquin Provincial Park (OMNR) and
University of Guelph. The following people assisted with eldwork:
M. Keevil, P. Moldowan, K. Hall, H. McCurdy-Adams and L. Monck-
Whipp. All work was carried out under an approved Laurentian University
Animal Care Committee protocol (AUP # 2008-12-02) and was authorised by
permits from OMNR.
Adamany, S., Salmon, M., and Witherington, B. (1997). Behavior of sea
turtles at an urban beach III. Cost and benets of nest caging as a
management strategy. Florida Scientist 60, 239253.
JWildlife Research J. L. Riley and J. D. Litzgus
Addiston, D. S. (1997). Galvanized wire nest cages can prevent nest
depredation. Marine Turtle Newsletter 76,811.
Ashmore, G. M., and Janzen, F. J. (2003). Phenotypic variation in smooth
softshell turtles (Apalone mutica) from eggs incubated in constant versus
uctuating temperatures. Oecologia 134, 182188.
Barton, B. T., and Roth, J. D. (2008). Implications of intraguild predation for
sea turtle nest protection. Biological Conservation 141, 21392145.
Bobyn, M. L., and Brooks, R. J. (1994). Incubation conditions as potential
factors limiting the northern distribution of snapping turtles, Chelydra
serpentina. Canadian Journal of Zoology 72,2837. doi:10.1139/z94-
Bolton, S. M., Marshall, S. A., and Brooks, R. J. (2008). Opportunistic
exploitation of turtles eggs by Tripanurga importuna (Walker) (Diptera:
Sarcophagidae). Canadian Journal of Zoology 86, 151160. doi:10.1139/
Booth, D. T. (2006). Inuence of incubation temperature on hatchling
phenotype in reptiles. Physiological and Biochemical Zoology 79,
274281. doi:10.1086/499988
Booth, D. T., Burgess, E., McCosker, J., and Lanyon, J. M. (2004). The
inuence of incubation temperature on post-hatching tness
characteristics of turtles. Intern. Congress Series 1275, 226233.
Breckenridge, W. (1960). A spiny soft-shelled turtle nest study.
Herpetologica 16, 284285.
Bull, J. J. (1985). Sex ratio and nest temperature in turtles: comparing eld and
laboratory data. Ecology 66, 11151122. doi:10.2307/1939163
Bull, J. J., and Vogt, R. C. (1981). Temperature-sensitive periods of sex
determination in emydid turtles. The Journal of Experimental Biology
218, 435440.
Burke, R. L., Schneider, C. M., and Dolinger, M. T. (2005). Cues used by
raccoons to nd turtle nests: effects of ags, human scent and diamond-
backed terrapin sign. Journal of Herpetology 39, 312315. doi:10.1670/
Choo, B. L., and Chou, L. M. (1987). Effect of temperature on the incubation
period and hatchability of Trionyx sirens Wiegmann eggs. Journal of
Herpetology 21, 230232. doi:10.2307/1564488
Christiansen, J. L., and Gallaway, B. J. (1984). Raccoon removal, nesting
success, and hatchling emergence in Iowa turtles with special reference to
Kinosternon avescens. The Southwestern Naturalist 29, 343348.
Converse, S. J., Iverson, J. B., and Savidge, J. A. (2002). Activity,
reproduction, and overwintering behavior of ornate box turtles
(Terrapene ornata ornata) in the Nebraska Sandhills. American
Midland Naturalist 148, 416422. doi:10.1674/0003-0031(2002)148
Correa-H, J. C., Cano-Constano, A. M., Paez, V. P., and Restrepo, A. (2010).
Reproductive ecology of the Magdalena River turtle (Podocnemis
lewyana) in the Mompos Depression Colombia. Chelonian
Conservation and Biology 9,7078. doi:10.2744/CCB-0784.1
Crouse, D. T., Crowder, L. B., and Caswell, H. (1987). A stage-based
population model for loggerhead sea turtles and implications for
conservation. Ecology 68, 14121423. doi:10.2307/1939225
Crowder, L. B., Crouse, D. T., Heppel, S. S., and Martin, T. H. (1994).
Predicting the impact of turtle excluder devices on loggerhead sea turtle
populations. Ecological Applications 4, 437445. doi:10.2307/1941948
Davy, C. M., and Murphy, R. W. (2009). Explaining patterns of deformity in
freshwater turtles using MacCullochs hypothesis. Canadian Journal of
Zoology 87, 433439. doi:10.1139/Z09-028
de Solla, S. R., Fernie, K. J., and Ashpole, S. (2008). Snapping turtles
(Chelydra serpentina) as bioindicators in Canadian Areas of Concern
in the Great Lakes Basin. II. Changes in hatching success and hatchling
deformities in relation to persistent organic pollutants. Environmental
Pollution 153, 529536. doi:10.1016/j.envpol.2007.09.017
Delmas, V., Baudry, E., Girondot, M., and Prevot-Julliard, A. (2007). The
righting response as a tness index in freshwater turtles. Biological
Journal of the Linnean Society. Linnean Society of London 91,
99109. doi:10.1111/j.1095-8312.2007.00780.x
Díaz-Paniagua, C., Keller, C., and Andreu, A. C. (1997). Hatching success,
delay of emergence and hatchling biometry of the spur-thighed tortoise,
Testudo graeca, in south-western Spain. Journal of Zoology (London,
England) 243, 543553. doi:10.1111/j.1469-7998.1997.tb02800.x
Doody, S. (1999). A test of comparative inuences of constant and uctuating
incubation temperatures on phenotypes of hatchling turtles. Chelonian
Conservation and Biology 3, 529531.
Du, W., and Ji, X. (2003). The effects of incubation thermal environments on
size, locomotor performance, and early growth of hatchling soft-shell
turtles, Pelodiscus sinensis. Journal of Thermal Biology 28, 279286.
Engeman, R. M., Martin, R. E., Constantin, B., Noel, R., and Woolard, J.
(2003). Monitoring predators to optimize their management for marine
turtle nest predation. Biological Conservation 113, 171178.
Engeman, R. M., Martin, R. E., Smith, H. T., Woolard, J., Crady, C. K.,
Constantin, B., Stahl, M., and Groninger, N. P. (2006). Impact on
predation of sea turtle nests when predator control was removed
midway through nesting season. Wildlife Research 33, 187192.
Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and
Canada.2nd edn. (Hopkins Fullllment Service: Baltimore, MD.)
Finkler, M. S., and Claussen, D. L. (1997). Use of the tail in terrestrial
locomotor activities of juvenile Chelydra serpentina. Copeia 1997,
884887. doi:10.2307/1447311
Fordham, D. A., Georges, A., and Brook, B. W. (2008). Indigenous harvest,
exotic pig predation and location persistence of a long-lived vertebrate:
managing a tropical freshwater turtle for sustainability and conservation.
Journal of Applied Ecology 45,5262. doi:10.1111/j.1365-2664.2007.
Frazer, N. B. (1992). Sea turtle conservation and halfway technology.
Conservation Biology 6, 179184. doi:10.1046/j.1523-1739.1992.
Freedberg, S., Stumpf, A. L., Ewert, M. A., and Nelson, C. E. (2004).
Developmental environment has long-lasting effects on behavioral
performance in two turtles with environmental sex determination.
Evolutionary Ecology Research 6, 739747.
Freedberg, S., Lee, C., and Pappas, M. (2011). Agricultural practices alter sex
ratios in a reptile with environmental sex determination. Biological
Conservation 144, 11591166. doi:10.1016/j.biocon.2011.01.001
Garber, S. D., and Burger, J. (1995). A 20-yr study documenting the
relationship between turtle decline and human recreation. Ecological
Applications 5, 11511162. doi:10.2307/2269362
García-Berthou, E. (2001). On the misuse of residuals in ecology: testing
regression residuals vs. the analysis of covariance. Journal of Animal
Ecology 70, 708711. doi:10.1046/j.1365-2656.2001.00524.x
Garrett, K., Wallace, B. P., Garner, J., and Paladino, F. V. (2010). Variations in
leatherback turtle nest environments: consequences for hatching success.
Endangered Species Research 11, 147155. doi:10.3354/esr00273
Gillingwater, S. D. (2001). A selective herpetofaunal survey, inventory and
biological research study of Rondeau Provincial Park. Unpublished report
to Rondeau Provincial Park, Morpeth, Ontario, Canada.
Gotelli, N. J., and Ellison, A. M. (2004). A Primer of Ecological Statistics.
(Sinauer Associates: Sunderland, MA.)
Hanson, J., Wibbels, T., and Martin, R. E. (1998). Predicted female bias in
sex ratios of hatchling loggerhead sea turtles from a Florida nesting
beach. Canadian Journal of Zoology 76, 18501861. doi:10.1139/z98-
Hawkes, L. A., Broderick, A. C., Godfrey, M. H., and Godley, B. J. (2007).
Investigating the potential impacts of climate change on a marine turtle
Effects of predator-exclusion cages on turtle nests Wildlife Research K
population. Global Change Biology 13, 923932. doi:10.1111/j.1365-
Heppel, S. S. (1997). On the importance of eggs. Marine Turtle Newsletter 76,
Hewavisenthi, S., and Parmenter, C. J. (2001). Inuence of incubation
environment on the development of the atback turtle (Natator
depressus). Copeia 2001, 668682. doi:10.1643/0045-8511(2001)001
Holt, S. M. (2000). Development and evaluation of a model for turtle
embryonic growth. Unpublished M.Sc. Thesis, Department of Biology,
University of Guelph, Guelph, Ontario.
Hughes, E. J., and Brooks, R. J. (2006). The good mother: does nest-site
selection constitute parental investment in turtles? Journal of Zoology 84,
Hutchison, V. H., Vinegar, A., and Kosk, R. J. (1966). Critical thermal
maxima in turtles. Herpetologica 22,3141.
Irwin, W. P., Horner, A. J., and Lohmann, K. J. (2004). Magnetic eld
distortions produced by protective cages around sea turtle nests:
unintended consequences for orientation and navigation? Biological
Conservation 118, 117120. doi:10.1016/j.biocon.2003.07.014
Janzen, F. J., and Paukstis, G. L. (1991). Environmental sex determination in
reptiles: ecology, evolution, and experimental design. The Quarterly
Review of Biology 66, 149179. doi:10.1086/417143
Kolbe, J. J., and Janzen, F. J. (2002). Spatial and temporal dynamic of turtle
nest predation: edge effects. Oikos 99, 538544. doi:10.1034/j.1600-
Kornaraki, E., Matossian, D. A., Mazaris, A. D., Matsinos, Y. G., and
Margaritoulis, D. (2006). Effectiveness of different conservation
measures for loggerhead sea turtle (Caretta caretta) nests at Zakynthos
Island, Greece. Biological Conservation 130, 324330. doi:10.1016/j.
Kurz, D. J., Straley, K. M., and DeGregorio, B. A. (2011). Out-foxing the red
fox: how to best protect the nests of the endangered loggerhead marine
turtle Caretta caretta from mammalian predation? Oryx 2011,16.
Les, H. L., Paitz, R. T., and Bowden, R. M. (2007). Experimental test of the
effects of uctuating incubation temperatures on hatchling phenotype. The
Journal of Experimental Zoology 307A, 274280. doi:10.1002/jez.374
Litzgus, J. D., Bolton, F., and Schulte-Hostedde, A. I. (2008). Reproductive
output depends on body condition in spotted turtles (Clemmys guttata).
Copeia 2008,8692. doi:10.1643/CH-07-093
Logan, M. (2010). Biostatistical Design and Analysis Using R, a Practical
Guide.(Wiley-Blackwell: Chichester, UK.)
Mahmoud, I. Y., Klicka, J., and Hess, G. L. (1973). Normal embryonic
stages of the western painted turtle, Chrysemys picta belli. Journal of
Morphology 141, 269279. doi:10.1002/jmor.1051410303
Mast, R. B., and Carr, J. L. (1989). Carapacial scute variation in Kemps
Ridley sea turtle (Lepidochelys kempi) hatchlings and juveniles. In
Proceedings of the First International Symposium on Kemps Ridley
Sea Turtle Biology, Conservation and Management. (Eds C. W. Caillouet
and A. M. Landry.) pp. 202219. (National Marine Fisheries Service and
Texas A&M University at Galveston: Galveston, TX.)
Matsuzawa, Y., Sato, K., Sakamoto, W., and Bjorndal, K. A. (2002). Seasonal
uctuations in sand temperature: effects on the incubation period
and mortality of loggerhead sea turtle (Caretta caretta) pre-emergent
hatchlings in Minabe, Japan. Marine Biology 140, 639646. doi:10.1007/
McKnight, C. M., and Gutzke, W. H. N. (1993). Effects of the embryonic
environment and of hatchling housing conditions on growth of young
snapping turtles (Chelydra serpentina). Copeia 1993, 475482.
Mersey Tobeatic Research Institute and Parks Canada (2009). Annual report
of research and monitoring in the greater Kejimkujik ecosystem 2008.
Mersey Tobeatic Research Institute and Parks Canada, Kempt, Nova
Scotia, Canada.
Mitchell, J. C., and Klemens, M. W. (2000). Primary and secondary effects
of habitat alteration. In Turtle Conservation. (Ed. M. W. Klemens.)
pp. 532. (Smithsonian Institution Press: Washington, DC.)
Mrosovsky, N., and Provancha, J. (1989). Sex ratio of loggerhead sea turtles
hatching on a Florida beach. Canadian Journal of Zoology 67,
25332539. doi:10.1139/z89-358
Mroziak, M. I., Salmon, M., and Rusenko, K. (2000). Do wire cages protect
sea turtles from foot trafc and mammalian predators? Chelonian
Conservation and Biology 3, 693698.
Mullins, M. A., and Janzen, F. J. (2006). Phenotypic effects of thermal means
and variances on smooth softshell turtle (Apalone mutica) embryos and
hatchlings. Herpetologica 62,2736. doi:10.1655/04-02.1
Neuwald, J. L., and Valenzuela, N. (2011). The lesser known challenge of
climate change: the variance and sex-reversal in vertebrates with
temperature-dependent sex determination. PLoS ONE 6, e18117.
Newbury, N., Khalil, M., and Venizelos, L. (2002). Population status and
conservation of marine turtles at El-Mansouri, Lebanon. Zoology in the
Middle East 27,4760. doi:10.1080/09397140.2002.10637940
OSteen, S. (1998). Embryonic temperature inuences juvenile temperature
and growth rate in snapping turtles Chelydra serpentina. The Journal of
Experimental Biology 201, 439449.
Ontario Ministry of Natural Resources (1998). Algonquin Provincial Park
Management Plan.(Queens Printer for Ontario: Ottawa, Canada.)
Packard, G. C., and Packard, M. J. (1998). Water relations of embryonic
snapping turtles (Chelydra serpentina) exposed to wet or dry
environments at different times in incubation. Physiological Zoology
Packard, G. C., Miller, K., Packard, M. J., and Birchard, G. F. (1999).
Environmentally induced variation in body size and condition in
hatchling snapping turtles (Chelydra serpentina). Canadian Journal of
Zoology 77, 278289.
Paitz, R. T., Clairardin, S. G., Grifn, A. M., Holgersson, M. C. N., and
Bowden, R. M. (2010). Temperature uctuations affect offspring sex but
not morphological, behavioral, or immunological traits in the northern
painted turtles (Chrysemys picta). Canadian Journal of Zoology 88,
479486. doi:10.1139/Z10-020
Perez-Heydrich, C., Jackson, K., Wendland, L. D., and Brown, M. B. (2012).
Gopher tortoise hatchling survival: eld study and meta-analysis.
Herpetologica 68, 334344. doi:10.1655/HERPETOLOGICA-D-11-
Plummer, M. V. (2010). Habitat use and movements of kingsnakes
(Lampropeltis getula holbrooki) in a partially abandoned and
reforested agricultural landscape. Herpetological Conservation Biology
5, 214222.
Prugh, L. R., Stoner, C. J., Epps, C. W., Bean, W. T., Ripple, W. J., Laliberte,
A. S., and Brashares, J. S. (2009). The rise of the mesopredator. Bioscience
59, 779791. doi:10.1525/bio.2009.59.9.9
Rafferty, A. R., and Reina, R. D. (2012). Arrested embryonic development:
a review of strategies to delay hatching in egg-laying reptiles. Proceedings
of the Royal Society. B: Biological Sciences 279, 22992308.
Rahman, S., and Burke, R. L. (2010). Evaluating nest protectors for turtle
conservation. In Final Reports of the Tibor T. Polgar Fellowship
Program. (Eds D. J. Yozzo, S. H. Fernald and H. Andreko.) pp. 123.
(Hudson River Foundation: New York, NY.)
Rasmussen, M. L., and Litzgus, J. L. (2010). Patterns of maternal investment
in spotted turtles (Clemmys guttata): implications of trade-offs, scales of
analyses, and incubation substrates. Ecoscience 17,4758. doi:10.2980/
Ratnaswamy, M. J., Warren, R. J., Kramer, M. T., and Adam, M. D. (1997).
Comparisons of lethal and nonlethal techniques to reduce raccoon
depredation of sea turtle nests. The Journal of Wildlife Management
61, 368376. doi:10.2307/3802593
LWildlife Research J. L. Riley and J. D. Litzgus
Reece, S. E., Broderick, A. C., Godley, B. J., and West, S. A. (2002). The
effects of incubation environment, sex, and pedigree on the hatchling
phenotype in a natural population of loggerhead turtles. Evolutionary
Ecology Research 4, 737748.
Reed, J. M., Fefferman, N., and Averill-Murray, R. C. (2009). Vital rate
sensitivity analysis as a tool for assessing management actions for the
desert tortoise. Biological Conservation 142, 27102717. doi:10.1016/
Refsnider, J. M., and Janzen, F. J. (2010). Putting eggs in one basket:
ecological and evolutionary hypotheses for variation in oviposition-site
choice. Annual Review of Ecology Evolution and Systematics 41,3957.
Rhen, T., and Lang, J. W. (1999). Temperature during embryonic and juvenile
development inuences growth in hatchling snapping turtles, Chelydra
serpentina. Journal of Thermal Biology 24,3341. doi:10.1016/S0306-
Ritchie, E. G., and Johnson, C. N. (2009). Predator interactions, mesopredator
release, and biodiversity conservation. Ecology Letters 12, 982998.
Rodríguez-Robles, J. A. (1998). Alternative perspectives on the diet of
gopher snakes (Pituophis catenifer, Colubridae): temperature records
versus stomach contents of wild and museum specimens. Copeia 1998,
463466. doi:10.2307/1447442
Rollinson, N., and Brooks, R. J. (2007). Marking nests increases the frequency
of nest depredation in a northern population of painted turtles (Chrysemys
picta). Journal of Herpetology 41, 174176. doi:10.1670/0022-1511
Roznik, E. A., and Alford, R. A. (2012). Does waterproong Thermochron
iButton dataloggers inuence temperature readings? Journal of Thermal
Biology 37, 260264. doi:10.1016/j.jtherbio.2012.02.004
Samson, J., Hughes, E. J., and Brooks, R. J. (2007). Excavation is a
nondeleterious method for obtaining fecundity and morphometric data
from small-sized eggs of freshwater turtles. Chelonian Conservation and
Biology 6, 255259. doi:10.2744/1071-8443(2007)6[255:EIANMF]2.0.
Schwarzkopf, L., and Brooks, R. J. (1985). Sex determination in northern
painted turtles: effect of incubation at constant and uctuating
temperatures. Canadian Journal of Zoology 63, 25432547.
Schwarzkopf, L., and Brooks, R. J. (1987). Nest-site selection and offspring
sex ratio in painted turtles, Chrysemys picta. Copeia 1987,5361.
Shine, R., LeMaster, M. P., Moore, I. T., Olson, M. M., and Mason, R. T.
(2001). Bumpus in the snake den: effects of sex, size, and body condition
on mortality of red-sided garter snakes. Evolution 55, 598604.
Smith, L. L., Steen, D. A., Conner, L. M., and Rutledge, J. A. (2013). Effects of
predator exclusion on nest and hatchling survival in the gopher tortoise.
The Journal of Wildlife Management 77, 352358. doi:10.1002/
Spencer, R., and Janzen, F. J. (2010). Demographic consequences of adaptive
growth and the ramications for conservation of long-lived organisms.
Biological Conservation 143, 19511959. doi:10.1016/j.biocon.2010.
Spinks, P. Q., Pauly, G. B., Crayon, J. J., and Shaffer, H. B. (2003). Survival of
the western pond turtle (Emys marmorata) in an urban California
environment. Biological Conservation 113, 257267. doi:10.1016/
Spotila, J. R. (2011). Saving Sea Turtles.(The John Hopkins University
Press: Baltimore, MD.)
Standing, K. L., Herman, T. B., and Morrison, I. P. (1999). Nesting ecology of
Blandings turtle (Emydoidea blandingii) in Nova Scotia, the northeastern
limit of the speciesrange. Canadian Journal of Zoology 77, 16091614.
Steen, D. A., and Gibbs, J. P. (2004). Effects of roads on the structure of
freshwater turtle populations. Conservation Biology 18, 11431148.
Steyermark, A. C., and Spotila, J. R. (2001). Effects of maternal identity
and incubation temperature on hatching and hatchling morphology in
snapping turtles, Chelydra serpentina. Copeia 2001, 129135.
Strickland, J., Colbert, P., and Janzen, F. J. (2010). Experimental analysis of
effects of markers and habitat structure on predation of turtle nests. Journal
of Herpetology 44,467470. doi:10.1670/08-323.1
Tomillo, P. S., Saba, V. S., Piedra, R., Paladino, F. V., and Spotila, J. R. (2008).
Effects of illegal harvest of eggs on the population decline of leatherback
turtles in Las Baulas Marine National Park, Costa Rica. Conservation
Biology 22, 12161224. doi:10.1111/j.1523-1739.2008.00987.x
Türkozan, O., Ilgaz, C., and Serdar, S. (2001). Carapacial scute variation in
loggerhead turtles, Caretta caretta. Zoology in the Middle East 24,
137142. doi:10.1080/09397140.2001.10637893
Weisrock, D. W., and Janzen, F. J. (1999). Thermal and tness-related
consequences of nest location in painted turtles (Chrysemys picta).
Functional Ecology 13,94101. doi:10.1046/j.1365-2435.1999.00288.x
Wibbels, T. (2003). Critical approaches to sex determination in sea turtles.
In The Biology of Turtles. 2nd edn. (Eds P. L. Lutz and J. A. Musick.)
pp. 104126. (CRC Press LLC: Boca Raton, FL).
Wilhoft, D. C., Hotaling, E., and Franks, P. (1983). Effects of temperature on
sex determination in embryos of the snapping turtle, Chelydra serpentina.
Journal of Herpetology 17,3842. doi:10.2307/1563778
Wilson, D. S. (1998). Nest-site selection: microhabitat variation and its effects
on the survival of turtle embryos. Ecology 79, 18841892. doi:10.1890/
Yerli, S., Canbolat, A. F., Brown, L. J., and Macdonald, D. W. (1997). Mesh
grids protect loggerhead turtle Caretta caretta nests from red fox Vulpes
vulpes predation. Biological Conservation 82, 109111. doi:10.1016/
Yntema, C. L. (1964). Procurement and use of turtle embryos for experimental
procedures. The Anatomical Record 149, 577585. doi:10.1002/ar.
Yntema, C. L. (1968). A series of stages in the embryonic development of
Chelydra serpentina. Journal of Morphology 125, 219251. doi:10.1002/
Yntema, C. L. (1979). Temperature levels and periods of sex determination
during incubation of eggs in Chelydra serpentina. Journal of Morphology
159,1727. doi:10.1002/jmor.1051590103
Effects of predator-exclusion cages on turtle nests Wildlife Research M
... Traffic volumes at PQP were 161-212 vehicles/h during fieldwork (Boyle et al., 2021). Fieldwork at APP was undertaken as part of a long-term turtle life-history project, which has been previously described Riley & Litzgus, 2013) but here we analyzed opportunistic on-road observations collected from a larger area of APP, beyond marked study populations, that includes a 60-km length of highway corridor bisecting the park. Summer average annual daily traffic volumes vary by highway segment and were 1250-4050 vehicles/day in 2016 (Ontario Ministry of Transportation, 2016). ...
... Adult survivorship (Armstrong et al., 2018;Brooks, Brown, & Galbraith, 1991;Keevil et al., 2018) and the fertility and body size relationship (Armstrong et al., 2018) have been previously estimated for this population. Published nest survival and hatching success estimates (Bobyn & Brooks, 1994a;Brooks et al., 1988;Brooks, Bobyn, et al., 1991;Riley & Litzgus, 2013;Rouleau et al., 2019) were combined with previously unpublished observations from 2014 to 2015 by weighted averaging according to the sample size (Appendix S1: Table S2). ...
Adult mortality is often the most sensitive vital rate affecting at‐risk wildlife populations. Therefore, road ecology studies often focus on adult mortality despite the possibility for roads to be hazardous to juvenile individuals during natal dispersal. Failure to quantify concurrent variation in mortality risk and population sensitivity across demographic states can mislead efforts to understand and mitigate the effects of population threats. To compare relative population impacts from road mortality among demographic classes, we weighted mortality observations by applying reproductive value analysis to quantify expected stage‐specific contributions to population growth. We demonstrate this approach for snapping turtles (Chelydra serpentina) observed on roads at two focal sites in Ontario, Canada, where we collected data for both live and dead individuals observed on roads. We estimated reproductive values using stage‐classified matrix models to compare relative population‐level impacts of adult and juvenile mortality. Reproductive value analysis is a tractable approach to assessing demographically variable effects for applications covering large spatial scales, non‐discrete populations, or where abundance data are lacking. For one site with long‐term life‐history data, we compared demographic frequency on roads to expected general population frequencies predicted by the matrix model. Our application of reproductive value is sex‐specific but, as juvenile snapping turtles lack external secondary sex characters, we estimated the sex ratio of road‐crossing juveniles after dissecting and sexing carcasses collected on roads at five sites across central Ontario. Juveniles were more abundant on roads than expected, suggesting a substantial dispersal contribution, and road‐killed juvenile sex ratio approached 1:1. A higher proportion of juveniles were also found dead compared to adults, and cumulative juvenile mortality had similar population‐level importance as adult mortality. This suggests that the impact of roads needs to be considered across all life stages, even in wildlife species with slow life histories, such as snapping turtles, that are particularly sensitive to adult mortality. This article is protected by copyright. All rights reserved.
... Worldwide, various methods have been trialed in attempts to protect turtle nests and other vulnerable native species from fox depredation: poison baits, shooting and trapping, and nest caging are a few examples (Fagerstone et al. 2004;Gentle et al. 2007;Riley and Litzgus 2013). Although these methods show short-term successes (e.g., Spencer 2000), in the long term they are generally not effective or are extremely labor-intensive to maintain indefinitely (Harding et al. 2001;Gentle et al. 2007;Spencer et al. 2016Spencer et al. , 2017. ...
... While nest caging is an effective method of nest protection (Riley and Litzgus 2013), protecting a small area of nesting beach and enticing female turtles to nest within is an alternative that has seen success in previous studies (e.g., Quinn et al. 2015), and if successful could be employed on a broad scale to increase recruitment. In this study, a nesting refuge structure design was tested in the summers of 2019-2020 and 2020-2021 at sites within the Bell's turtles' range. ...
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Invasive red foxes (Vulpes vulpes) are a serious conservation issue for Australia's freshwater turtle species, including the endangered Bell's turtle (Myuchelys bellii). As many as 96% of Australian freshwater turtle nests may be depredated in a season by foxes. Current methods of turtle nest protection rely on early detection of nesting activity, followed by nest-specific structures to prevent predation. An alternative method to provide protection against fox raiding was tested: nesting refuge structures based on a design successfully used in the United States to protect diamondback terrapin (Malaclemys terrapin) nests. Six wood and chicken wire structures were placed at different sites beside large riverine pools on the Macdonald and Gwydir rivers, northeastern New South Wales, Australia, in the summers of 20192020 and 20202021. Sites were chosen for known previous nesting activity or presence of mature females, and each structure was placed in typical Bell's turtle nesting habitat at known nesting sites. Prior to placement, the soil was tilled with a rotary hoe to make the interior of the structure more enticing as nesting habitat, because Bell's turtles had been previously seen to nest in disturbed soils. Although females did approach the structures and in one case entered, no females were recorded nesting inside. Further, severe flooding in both years damaged and/or displaced 4 of the 6 structures. Rigid nest protection structures were therefore not shown to be an effective nest protection method for this species, despite their success in other regions for other species. Negative results such as these are important for conservation studies because they guide conservation efforts away from expending limited resources on ineffective methods and strategies.
... However, depredated nests can be observed throughout the whole incubation period (Riley and Litzgus, 2014). Therefore, to protect chelonian populations from nest predation, various predator-exclusion approaches have been used in conservation actions (Buhlmann and Osborn, 2011;Riley and Litzgus, 2013;Schindler et al., 2017). ...
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The viability of many turtle species, including the European pond turtle (Emys orbicularis), is imperilled by nest depredation. Depredation rates of the E. orbicularis population in eastern Slovakia are high; therefore, we aimed to identify nest predators and to determine which sensory cues they use to find the nests. From the set of different experimental trials with artificial nests in the field, only the application of turtle-scented water imitating the female migration path to the nesting site suggested potential predation of turtle nests driven by olfactory cues. Although we did not observe depredation of the installed artificial nests, we identified badgers (Meles meles), wildcats (Felis silvestris), and wild boars (Sus scrofa) as potential predators. Our results also imply that the use of chemical repellents should be considered for nest protection of the study species in Tajba National Nature Reserve.
... In 2013 and 2014, we incubated all nests in situ (i.e., where oviposited) under natural conditions and protected them from predation with hardware cloth caging; this type of predator excluder is unlikely to affect nest temperatures (Riley and Litzgus, 2013;Burke et al., unpublished data). Immediately after oviposition and prior to installing predator excluders, we carefully excavated all nests by hand, recorded clutch sizes, and promptly returned all eggs to their nest cavities. ...
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Wood turtles (Glyptemys insculpta) have been suffering range-wide population declines since the 1900s. Most monitoring efforts of these turtles involve population surveys to assess population size and viability but relatively few investigate rates of reproductive success. We collected four consecutive years (2013–2016) of wood turtle nesting data at a nesting site in northwestern New Jersey; population-level hatching success was unusually low. Furthermore, annual, intra-individual hatch rates and comparisons between natural and artificial incubation revealed that approximately half of all females usually produced clutches with low (<50%) hatch rates, regardless of incubation conditions. In contrast, the annual hatch rates of other females were either consistently high (>50%) or highly variable, ranging from 0 to 100%. Thus, some adult females are potentially making much larger contributions to the next generation than others. A repeatability analysis suggested that approximately 60% of the hatch rate variability observed in this population can be attributed to maternal identity. The remaining 40% may be attributed to the random environmental factors that are often theorized to be potential reasons for reduced hatch rates in turtle populations (e.g., unsuitable incubation conditions, flooding, desiccation, egg infertility, egg damage due to improper handling by researchers, root and insect predation, and microbial infection). The ultimate causes of this population’s hatching success variability are uncertain, but maternally-linked hatching failure in turtle populations could be associated with inbreeding, infertility, senescence, inadequate maternal diets, or environmental contamination. This study indicates that commonly suggested hypotheses for hatching failure, such as unsuitable incubation conditions or infertility, are unlikely to explain all of the hatch rate variability in some turtle populations. This study also reveals a cryptic conservation implication for vulnerable turtle populations: that the presence of many nesting females and nests does not necessarily assure high or even sustainable reproductive rates. When coupled with the high rates of nest predation and low juvenile survival rates that are common in most turtle populations, the exceedingly low hatch rates observed in this population suggest that recruitment in some turtle populations could be severely hindered even when nests are protected in the field or incubated in laboratory settings.
... There are several solutions for the size and design of nesting grids and cages. Riley and Litzgus (2013) used belowground and aboveground cages and wooden-sided nest cages. Aboveground cages may attract multiple predators, but their effectiveness was excellent with only two nests being predated across the three design treatments. ...
... Locating intact turtle nests and covering them with predator-exclusion screens or cages can also be effective for inhibiting both foxes and other predators (Graham 1997;Riley and Litzgus 2013). This technique proved more effective than lethal fox control via trapping and den fumigation for protecting eggs of Australian sea turtles (O'Connor et al. 2017). ...
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It has been asserted that introduced red foxes (Vulpes vulpes) destroy ∼95% of nests of freshwater turtles in south-eastern Australia, are more efficient predators of freshwater turtle nests than Australian native predators, and are driving Australian freshwater turtle species to extinction. Available information was reviewed and analysed to test these assertions. Nest predation rates for all predators including foxes averaged 70% across Australia and 76% for south-eastern Australia compared to 72% for North America where freshwater turtles co-exist with many native predators, including foxes. Predation rates on Australian freshwater turtle nests did not differ significantly where foxes were included in the identified nest predators and where they were not, but sample sizes were very small. Evidence was lacking of foxes being the primary driver of population declines of Australian freshwater turtles, and some turtle populations are stable or increasing despite exposure to fox predation. Australian native species can be effective nest predators, and their role has probably been usurped by foxes to some degree. Where research shows that increased recruitment is necessary to conserve Australian freshwater turtle populations, strategies such as electric fencing of nesting beaches, nest protection cages and ex situ incubation of turtle eggs will probably be more cost-effective than efforts to reduce fox numbers. Further research is also needed to better understand the biological and environmental factors that regulate nest predation rates.
... 'Nest protection'. To reduce nest predation rates, various types of predator exclusion devices are designed for a wide range of freshwater and marine turtle species (Riley and Litzgus 2013;Buzuleciu et al. 2015;Schindler et al. 2017). Until now, square metal grids attached to the ground (similar to design C presented by Schindler et al. 2017) have been used for the protection of turtle nests in the Tajba NNR. ...
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The European pond turtle ( Emys orbicularis ) is the only native freshwater turtle species in Slovakia. Due to watercourse regulations in the middle of the 20 th century, its range became fragmented and, currently, there are only two isolated populations. From a total of 1,236 historical records in Slovakia, most observations (782 records) came from the area of the Tajba National Nature Reserve (NNR). Three of the population viability analysis models (‘baseline’, ‘catastrophe’, ‘nest protection during a catastrophe’) indicated the extinction of the population in Tajba, with the highest probability of extinction occurring during a catastrophic event (probability of extinction 1.00). We also evaluated information about the activity patterns of seven radio-tracked individuals and about the number of destroyed nests from the area. During the period 2017–2021, we recorded only two turtles leaving the aquatic habitat of Tajba. An alarming fact is the massive number of destroyed nests found in the area during the study period (Tajba 524; Poľany 56). Our results indicate that the population in the Tajba NNR require immediate application of management steps to ensure its long-term survival.
... We reburied eggs in their original orientation and position within the nest chamber and installed an above-ground hardware cloth (0.63 cm galvanized wire) nest cage (30 cm diameter) to protect the nests from predators. This style of predator-exclusion cage does not interfere with nest temperature or soil moisture (Riley and Litzgus, 2013) and, because they were applied to all sites, are expected to have consistent effects, if any. At the beginning of August, three openings (5x5 cm) were cut in each predator-exclusion cage to allow hatchlings to escape. ...
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At present, some 11,440 extant reptile species have been described on Earth and several hundred new species have been described each year since 2008 (Uetz & Hosek 2018). As grazers, seed dispersers, predators, prey and commensal species, reptiles perform crucial functions in ecosystems (Böhm et al. 2013). Reptiles are a hugely diverse group of animals (Pincheira-Donoso et al. 2013) and are adapted to live in a wide range of tropical, temperate and desert terrestrial habitats, as well as freshwater and marine environments (Böhm et al. 2013). That said, reptile species usually have narrower geographic distributions than other vertebrate taxonomic groups (e.g. birds or mammals), and this coupled with particular life history traits makes some reptile species particularly vulnerable to anthropogenic threats (Böhm et al. 2013, Fitzgerald et al. 2018). For example, some turtle species are 16 typically very long lived, take years to reach full maturity, produce small clutches and have variable reproductive success, which means that they are vulnerable to loss of adults and take many years to recover from declines (Congdon et al. 1994). Multiple threats to reptile populations have been identified and are implicated in species declines (Gibbons et al. 2000, Todd et al. 2010). These threats include habitat modification, loss and fragmentation (Neilly et al. 2018, Todd et al. 2017), environmental contamination (Sparling et al. 2010), potentially unsustainable harvesting and/or collection (van Cao et al. 2014), invasive species (Fordham et al. 2006), climate change (Bickford et al. 2010, Sinervo et al. 2010) and disease and parasitism (Seigel et al. 2003). Also, due to their physical characteristics, reputation (warranted or otherwise) and in some cases venomous bites, some reptile species are viewed with distaste, which leads to apathy around their conservation (Gibbons et al. 1988). According to the IUCN Red List, of 10,148 reptile species that have been assessed, some 21% are considered to be threatened (IUCN 2021). Extinction risks are particularly high in tropical regions, on oceanic islands and in freshwater environments (Böhm et al. 2013), with some 59% of turtle species assessed at risk of extinction (van Dijk et al. 2014). Reptiles with specialist habitat requirements and limited ranges that are in areas accessible to humans are likely to face greater extinction risks (Böhm et al. 2016). Many island reptile species are endemic and are therefore even more vulnerable to extinction as a result of human disturbance (Fitzgerald et al. 2018). For a comprehensive summary of threats to different families of reptiles see Fitzgerald et al. (2018). Evidence-based knowledge is key for planning successful conservation strategies and for the cost-effective allocation of scarce conservation resources. To date, reptile conservation efforts have involved a broad range of actions, including protection of eggs, nests and nesting sites; protection from predation; translocations; captive breeding, rearing and releasing; habitat protection, restoration and management; and addressing the threats of accidental and intentional harvesting. However, most of the evidence for the effectiveness of these interventions has not yet been synthesised within a formal review and those that have could benefit from periodic updates in light of new research. Targeted reviews are labour-intensive and expensive. Furthermore, they are ill-suited for subject areas where the data are scarce and patchy. Here, we use a subject-wide evidence synthesis approach (Sutherland et al. 2019) to simultaneously summarize the evidence for the wide range of interventions dedicated to the conservation of all reptiles. By simultaneously targeting all interventions, we are able to review the evidence for each intervention cost-effectively, and the resulting synopsis can be updated periodically and efficiently. The synopsis is freely available at and, alongside the Conservation Evidence online 17 database, is a valuable asset to the toolkit of practitioners and policy makers seeking sound information to support reptile conservation. We aim to periodically update the synopsis to incorporate new research. The methods used to produce the Reptile Conservation Synopsis are outlined below. This synthesis focuses on global evidence for the effectiveness of interventions for the conservation of reptiles. This subject has not yet been covered using subject-wide evidence synthesis. This is defined as a systematic method of reviewing and synthesising evidence that covers broad subjects (in this case conservation of multiple taxa) at once, including all closed review topics within that subject at a fine scale, and analysing results through study summary and expert assessment, or through meta-analysis. The term can also refer to any product arising from this process (Sutherland et al. 2019). This global synthesis collates evidence for the effects of conservation interventions on terrestrial, aquatic and semi-aquatic reptiles, including all reptile orders, i.e. Crocodilia (alligators, crocodiles and gharials), Testudines (turtles and tortoises), Squamata (snakes, lizards and amphisbaenians) and Rhynchocephalia (tuatara). This synthesis covers evidence for the effects of conservation interventions for wild reptiles (i.e. not in captivity). We have not included evidence from the substantial literature on husbandry of marine and freshwater reptiles kept in zoos or aquariums. However, where these interventions are relevant to the conservation of wild declining or threatened species, they have been included, e.g. captive breeding for the purpose of increasing population sizes (potentially for reintroductions) or gene banking (for future release).
Procyon lotor (Raccoon) are a dominant predator on eggs of Malaclemys terrapin (Diamondback Terrapin), an estuarine specialist turtle endemic to saltmarshes of the eastern and gulf coasts of the United States. The purpose of this study was to determine if broadcast predator vocalizations could potentially deter Raccoons from foraging on Diamondback Terrapin eggs. We used artificial nests arrays to test 2 hypotheses: (1) predator vocalization playbacks (barking Canis lupus familiaris [Domestic Dog]) reduce number of artificial nests depredated by Raccoons compared to non-predator vocalization playbacks (Urocyon cinereoargenteus [Gray Fox]) or control treatments (no playbacks), and (2) predator vocalization playbacks reduce frequency of visits by Raccoons and overall foraging time compared to non-predator playbacks and control treatments. We randomly assigned sound treatments to each night of a 3-day trial, with 3 trials conducted at 4 experimental sites. We counted the number of depredated artificial nests and used trail cameras to document number of Raccoon visits and Raccoon foraging time following each sound treatment. On average, 51% of artificial nests were depredated in the predator vocalization treatments, 66% in the non-predatorvocalization treatments, and 81% of nests in the control treatments. Average number of Raccoon visits was about 3 times higher in the control treatment compared to the predator treatment but auditory treatment did not affect time spent foraging. Response to predator vocalization was attenuated by repeated exposure to recorded predator playbacks. Variation in type of predator vocalization, length, and frequency of playbacks may increase effectiveness of auditory deterrents on predators of Diamondback Terrapin nests.
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All sea turtle nests at Boca Raton, Palm Beach Co., Florida, U.S.A., are epowsed to foot traffic from visitors that use the beach, and to predators (raccoons, foxes, and sknks) that feed upon the egg and hatchlings of marine turtles. To protect the nests, managers have covered them with square wire cages anchored in the sand. We compared the fate of caged and uncaged nests exposed to high and low levels of food traffic, and to high and low levels of predation. We found no evidence that foot traffic posed a threat to the nests. Predators (mostly raccoons) used the cages as landmarks to locate nests. Predators reduced hatchling productivity on the beach more during the year of our study (1996) than during the following year when cages were not used. We conclude that the cages used failed to protect the nests. We recommend that at this and at other sites were similar conditions exist, management efforts should shift away from efforts to discourage mammalian predators and toward efforts to reduce predator populations adjacent to the nesting beach.
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Hatching success, egg incubation, emergence and hatchling characteristics were assessed for 44 naturally incubating nests of Testudo graeca in south-western Spain. Nest predation rate was 4.5% and overall hatching success was 82.4%. Incubation periods ranged from 78 to 114 days, and hatchlings delayed emergence from the nest from one to 23 days. Emergences occurred from mid August to late September, and were not correlated with nesting dates, but earlier laid nests had longer incubation times, which was probably owing to lower temperatures experienced by clutches laid at the beginning of the nesting season. Variance of hatchling body size and mass was high and was mainly influenced by the gravid female. Mean straight carapace length was 34.14 mm, and mean body mass 10.8 g. Hatchlings from clutches laid last in the nesting season had significantly better physical condition. Hatchling mass was positively correlated with egg mass, and both variables were positively correlated with emergence date. Both better physical condition and relatively late emergence may confer advantages to hatchlings in the face of unfavourable environmental conditions in autumn.
R - the statistical and graphical environment is rapidly emerging as an important set of teaching and research tools for biologists. This book draws upon the popularity and free availability of R to couple the theory and practice of biostatistics into a single treatment, so as to provide a textbook for biologists learning statistics, R, or both. An abridged description of biostatistical principles and analysis sequence keys are combined together with worked examples of the practical use of R into a complete practical guide to designing and analyzing real biological research. Topics covered include: simple hypothesis testing, graphing. exploratory data analysis and graphical summaries. regression (linear, multi and non-linear). simple and complex ANOVA and ANCOVA designs (including nested, factorial, blocking, spit-plot and repeated measures). frequency analysis and generalized linear models. Linear mixed effects modeling is also incorporated extensively throughout as an alternative to traditional modeling techniques. The book is accompanied by a companion website with an extensive set of resources comprising all R scripts and data sets used in the book, additional worked examples, the biology package, and other instructional materials and links.
Flexible-shelled eggs of common snapping turtles (Chelydra serpentina) were halfburied in wet (water potential = -150 kPa) or dry vermiculite (water potential = -950 kPa), and then were incubated in covered containers at 29.0 C. Half the eggs on each substrate were transferred to the other substrate at the end of the first trimester of development, and half the eggs were transferred between wet and dry substrates at the end of the second trimester. Thus, the experiment conformed with a 2₃ factorial design in which eight treatment groups were recognized on the basis of the hydric conditions encountered by eggs during each of the three trimesters of incubation (wetwet-wet, wet-wet-dry, etc.). Hydric conditions encountered at any time during incubation affected the pattern of net water exchange between eggs and their surroundings and also influenced the size of hatchlings and the amount of residual yolk available to sustain emergent young. Size of hatchlings was positively correlated with net water exchange by eggs, but mass of the residual yolk was negatively correlated with net water exchange. Thus, water exchanges occurring at any time in incubation seemingly influence the size of the pool of water available inside eggs, and the size of this pool of water, in turn, affects physiological processes that influence body size and nutrient reserves in hatchlings.
Abstract Huge breeding aggregations of red-sided garter snakes (Thamnophis sirtalis parietalis) at overwintering dens in Manitoba provide a unique opportunity to identify sources of mortality and to clarify factors that influence a snake's vulnerability to these factors. Comparisons of sexes, body sizes, and body condition of more than 1000 dead snakes versus live animals sampled at the same time reveal significant biases. Three primary sources of mortality were identified. Predation by crows, Corvus brachyrhynchos (590 snakes killed), was focussed mostly on small snakes of both sexes. Crows generally removed the snake's liver and left the carcass, but very small snakes were sometimes brought back to the nest. Suffocation beneath massive piles of other snakes within the den (301 dead animals) involved mostly small males and (to a lesser extent) large females; snakes in poor body condition were particularly vulnerable. Many emaciated snakes (in= 142, mostly females) also died without overt injuries, probably due to depleted energy reserves. These biases in vulnerability are readily interpretable from information on behavioral ecology of the snakes. For example, sex biases in mortality reflect differences in postemergence behavior and locomotor capacity, the greater attractiveness of larger females to males, and the high energy costs of reproduction for females.
Sex is determined by incubation temperature in many reptiles, but precise quantifications of these effects have been obtained only in the laboratory. Here, temperatures and sex ratios were studied from 75 clutches of map turtles incubated in their natural nests. Clutch sex ratio showed a clear association with each of the two measures of nest temperatures studied: (1) hours per day above 30@? or 32@?C, and (2) the mean and variance of nest temperature. The best associations with sex ratio were obtained from temperatures experienced during the 4th through 7th wk of development and from temperatures during July. Results from this study were similar in several respects to results from previous laboratory studies on sex determination, despite the fact that natural incubation entails fluctuating temperatures and other environmental effects not incorporated in most laboratory studies.