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2006 SOUTHEASTERN NATURALIST 5(1):175–183
Monthly and Daily Activity of a Fossorial Lizard,
KYLE G. ASHTON1,2,*, AND SAM R. TELFORD, JR.3
Abstract - Here we evaluate monthly and daily activity patterns of Neoseps
Reynoldsi (Sand Skink), through examination of museum specimens and population
studies at Archbold Biological Station (ABS), Highlands County, FL, and in Ocala
National Forest (ONF), Marion County, FL. Sand Skinks are active throughout the
year, with highest captures in February through May, and August through October.
Museum specimen data suggest a peak in December, but this reflects collector bias.
Number of captures is significantly negatively related to precipitation and positively
related to temperature for Sand Skinks at ABS, but this relationship is due to capture
of hatchlings from July through October. At ONF, no relationship between temperature
and precipitation and number of captures exists. The number of Sand Skink
tracks per day at ABS is not related to temperature, but is significantly negatively
related to precipitation.
Temperature and precipitation influence activity of lizards on a daily,
monthly, and seasonal basis (e.g., Grant and Dunham 1990, Huey and
Pianka 1977, Pianka 1986). In tropical areas, which have relatively
aseasonal temperatures but highly seasonal patterns of precipitation
(wet and dry seasons), activity of lizards tends to be greatest during the
wet season (e.g., James 1994, Lister and Aguayo 1992). In contrast, in
temperate regions, which have relatively aseasonal patterns of precipitation
but highly seasonal temperatures, activity of lizards tends to be
limited by very warm or very cold temperatures (e.g., Fitch 1958, Grant
and Dunham 1990, Pianka 1970).
In addition to temperature and precipitation, the timing of reproductive
events also influences activity of lizards. In particular, lizards tend to be
more active during the breeding season (Fitch 1958, Lister and Aguayo
1992, Pianka 1970), but it is difficult to separate the influence of temperature
and precipitation from reproductive phenology because the timing of
reproduction is itself cued by temperature and precipitation (Duvall et al.
1982). Regardless, it is well established that temperature, precipitation,
and timing of reproductive events (particularly breeding) influence activity
1Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862. 2Current address
- Division of Biological Sciences, University of California at San Diego, 9500
Gilman Drive, MC 0116, La Jolla, CA 92093. 3The Florida Museum of Natural
History, University of Florida, Gainesville, FL 32611. *Corresponding author -
176 Southeastern Naturalist Vol. 5, No. 1
Here we evaluate monthly and daily activity patterns of Neoseps
reynoldsi Stejneger (Sand Skink) relative to temperature, precipitation,
and timing of reproductive events. Activity patterns of Sand Skinks are of
interest for at least two reasons. First, most research on the effects of
temperature and precipitation on activity patterns of lizards has been
conducted in temperate or tropical regions. Sand Skinks occur in a subtropical
environment. Subtropical environments differ from temperate
and tropical environments because they exhibit seasonality in both precipitation
and temperature, providing an opportunity to evaluate lizard
activity patterns in response to both environmental cues. Second, most
studies of activity have focused on terrestrial or arboreal lizards. Sand
Skinks are fossorial and, despite the presence of fossorial lizards on at
least three different continents (Pianka 1986), activity patterns of fossorial
lizards are poorly known.
Patterns of monthly activity
To evaluate monthly patterns of activity of Sand Skinks, we used three
datasets. The first dataset consists of museum specimens. We examined all
available museum specimens (list available from K.G. Ashton) and compiled
month of collection for specimens with known collection dates (n =
225). For this dataset, individuals collected throughout the range of Sand
Skinks are lumped together.
The second dataset is from a population study conducted from February
2002 through January 2003 near the southern extent of the range of Sand
Skinks at Archbold Biological Station (ABS), Highlands County, FL
(464758, 3008716 UTM). Fifty-six bucket traps were placed in long-unburned
rosemary scrub habitat. Traps were arranged in a 7 x 8 grid, with
traps spaced 6.7 m apart (total trapping area = 40 x 47 m). Each 18.9-L
bucket was sunk a few cm below the sand surface and covered with a 30- x
30-cm lid of masonite or hard plastic propped 2 cm above the bucket by four
wooden pegs. Sand was placed in the bottom of each bucket. Traps were
checked every two to three days, and water was added to the sand at each
checking. Each Sand Skink was measured and marked (toe clipping) in the
field, then released immediately after capture.
The third dataset consists of individuals captured in a population study
conducted from June 1997 through May 1998 near the northern extent of the
range of Sand Skinks in Ocala National Forest (ONF), Marion County, FL
(R25E, T12S, S4). This study took place in Pinus palustris Mill (longeaf
pine)-Quercus laevis Walt (turkey oak) sandhill habitat. A 20- x 20-m
enclosure was constructed of aluminum flashing buried 30 cm in the sand.
Sixteen pitfall drift fences, including 2 m of aluminum flashing with two
3.8-L buckets sunk into the sand at each end, were evenly spaced within the
2006 K.G. Ashton, and S.R. Telford, Jr. 177
enclosure. An additional 3.8-L bucket was placed every 5 m along the
interior and exterior of the enclosure flashing. Additional buckets were
placed at 5-m intervals, extending 10 m in each direction, outside of the
enclosure. The total trapping area was 40 x 40 m and included 148 buckets.
Each bucket contained at least 10 cm of sand, was countersunk to a depth of
13 cm and covered by a masonite board (41 cm2) resting on the surface of the
sand. Each bucket was checked once per week, and all captures were taken to
a laboratory for processing. Snout-vent length was measured for each individual.
All individuals were released at capture sites within three to seven
days of capture.
For each site, we partitioned captures into hatchlings (≤ 35 mm SVL),
juveniles (> 35 mm, but < 45 mm SVL) and adults (≥ 45 mm SVL; Sutton
1996, Telford 1959). We plotted the number of individuals of each age
category caught per month for each site to examine monthly variation in
activity and evaluate the effect of hatchling emergence on number of captures.
We used multiple regression analysis in combination with backward
stepwise multiple regression to test for relationships between mean maximum
temperature, total precipitation, and the total number of lizards
captured per month at each site. Prior to each analysis, data that violated
the assumptions of regression analysis were transformed using log (X+1)
transformation, except in one case (ABS temperature data) with leftskewed
data, for which we used the X2 transformation. Weather data for
the ONF site (Fig. 1) were obtained from the Florida Climate Center
(http://www.coaps.fsu.edu/climate_center/) by averaging data from
weather stations at Ocala and Crescent City, FL, because the study site
was geographically intermediate. Weather data for ABS (Fig. 1) were
collected by staff at ABS.
Patterns of daily activity
To evaluate the effect of temperature and precipitation on daily activity,
we used information from a study of Sand Skink tracks conducted
from November 2001 through October 2002 at ABS (a different area and
habitat than used for the population study at ABS). For this study, we
used a 3- x 75-m area of scrubby flatwoods habitat that was adjacent to an
8-m wide sand firelane. Surveys of the scrubby flatwoods area were conducted
for 14 days each month. Each day of monitoring consisted of one
of us (KGA) walking the study plot and counting the number of Sand
Skink tracks (distinct, sinusoidal tracks; Andrews 1994, Telford 1959)
present. Tracks were considered distinct if discontinuous from other
tracks and located > 1 m from any other track. Given that rainfall erases
tracks, it is important that surveys are conducted before rains occur. On
days without rain (mostly during the non-rainy season from October
through May), track surveys were conducted at the end of the day, just
before sunset. On days with rain (predicted from forecasts and mostly
178 Southeastern Naturalist Vol. 5, No. 1
during the rainy season from June through September), track surveys
were conducted just prior to the onset of rains. In this way tracks could be
Table 1. Mean number of Sand Skink tracks, mean maximum air temperature, and mean total
precipitation per day for each 14-day monthly sampling period from November 2001 through
October 2002 at one site at Archbold Biological Station, Highlands County, FL. For simplicity,
data are presented as January through December. Tracks = mean total number of Sand Skink
tracks/day; Temp. = mean daily maximum air temperature (°C); Precip. = mean total precipitation/
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Tracks 3.1 0.5 2.1 4.1 1.4 0 0.8 1.9 1.1 1.4 2.9 3.3
Temp. 28.0 24.6 28.2 32.0 34.2 32.5 33.7 33.4 32.6 30.7 27.4 27.3
Precip. 0.00 0.08 0.01 0.00 0.55 1.76 0.92 0.11 1.10 0.22 0.00 0.03
Figure 1. Temperature and precipitation for A) Archbold Biological Station (February
2002 through January 2003), and B) Ocala National Forest (from average of
weather data from June 1997 through May 1998 for Ocala and Crescent City weather
stations). For simplicity, data are presented as January through December.
2006 K.G. Ashton, and S.R. Telford, Jr. 179
checked before being erased by rainfall. If rains stopped prior to sunset, a
track survey was also conducted just before sunset. In cases where more
than one track survey was conducted on the same day, the number of
tracks was summed to produce the total number of tracks for that day. It
is assumed that Sand Skink tracks were not made during rainfall. All
Sand Skink tracks were wiped away by hand as each survey was conducted.
Thus, any tracks present on subsequent surveys were caused by
new surface activity of Sand Skinks occurring after the last survey.
Maximum air temperature and total precipitation were compiled for each
day that tracks were counted. To evaluate the relationship between surface
activity (as indicated by tracks), air temperature, and precipitation, we first
calculated the mean number of tracks/day, mean maximum air temperature/
day, and mean total precipitation/day for each monthly monitoring period
(Table 1). Prior to conducting multiple regression and backward stepwise
multiple regression analyses to test the dependence of Sand Skink tracks on
precipitation and air temperature across months, we log (X+1) transformed
Patterns of monthly activity
Museum specimens were collected during every month, indicating yearround
activity (Fig. 2a). Most individuals were collected from February
through May (peak in February), with relatively few individuals collected
throughout the rest of the year, with the exception of December. At ABS,
Sand Skinks were captured in every month except January (Fig. 2b). Most
captures occurred between February and May (peak in March). Captures
were few for all other months, except August. At ONF, Sand Skinks were
captured from April to June (peak in May), in August and October, but not in
any other month (Fig. 2c).
At ABS, number of Sand Skinks captured per month was significantly
related to monthly mean maximum temperature and total monthly precipitation
(multiple r2 = 0.56, df = 2,9, F = 5.82, P < 0.05), with a positive
relationship between monthly captures and temperature (β = +0.76) and a
negative relationship between monthly captures and precipitation (β =
-0.60). However, backward stepwise multiple regression analysis revealed
that neither temperature nor precipitation alone were significant
predictors of monthly captures at ABS. At ONF, monthly captures was
not related to temperature or precipitation (multiple r2 = 0.34, df = 2,9, F
= 2.27, P > 0.05).
Analyses of monthly activity of Sand Skinks are confounded by captures
of hatchlings in July through October (Fig. 2) because new individuals are
added to the population. Thus, we also tested for relationships between
monthly captures and temperature and precipitation using only captures of
180 Southeastern Naturalist Vol. 5, No. 1
Figure 2. Monthly distribution of captures based on A) museum specimens, B) a
population study at Archbold Biological Station from Feb. 2002 through Jan. 2003,
and C) a population study at Ocala National Forest from June 1997 through May
1998. For simplicity, data are presented as January through December.
2006 K.G. Ashton, and S.R. Telford, Jr. 181
juveniles and adults. Number of juveniles and adults collected each month at
ABS (multiple r2 = 0.38, df = 2,9, F = 2.77, P > 0.05) and at ONF (multiple r2
= 0.32, df = 2,9, F = 2.08, P > 0.05) failed to show a significant relationship
with temperature and precipitation.
Patterns of daily activity
Sand Skink tracks were most abundant in April, and November through
January; tracks were least common in June and July (Table 1). Across
months, the mean number of Sand Skink tracks per day was significantly
related to mean maximum daily air temperature and mean total daily precipitation
(multiple r2 = 0.61, df = 2,9, F = 7.06, P < 0.05). Backward stepwise
multiple regression revealed precipitation as the only significant predictor of
Sand Skink tracks, with a negative relationship between tracks and precipitation
(β = -0.74; r2 = 0.54, df = 1,10, F = 11.83, P < 0.01).
Sand Skinks can be captured every month of the year (Fig. 2). Most
specimens are captured between February and May, with low numbers of
captures for most other months. Many museum specimens were collected in
November and December, but field study does not corroborate this result.
Instead, our field studies suggest a second peak of captures in August
through October. Field studies of populations in Marion County, FL (Smith
1982), and in Orange and Osceola Counties, FL (Sutton et al. 1999), show
similar peaks in the number of captures (February through May, and September).
At ABS (Fig. 2b), ONF (Fig. 2c), and in Orange and Osceola
Counties (Sutton et al. 1999), peak captures is in March (ABS), April
(Orange and Osceola Counties) or May (ONF), which may indicate geographic
variation in the peak of monthly activity (ABS is the furthest south
and ONF is the furthest north). The large number of museum specimens
from February, November, and December reflects time of collection of
mainly three researchers (N.R. Wood, R.H. Mount, and one of us, S.R.
Telford) rather than indicating levels of activity.
Timing of reproductive events is associated with number of captures of
Sand Skinks. Sand Skinks mate between February and May (Ashton 2005,
Telford 1959). The greatest numbers of Sand Skinks are captured during this
time period (Fig. 2), indicating increased activity during the mating season,
similar to other lizards (e.g., Lister and Aguayo 1992, Pianka 1970). Females
lay eggs principally in June, and hatchlings emerge in late July
(Ashton 2005, Telford 1959). The emergence of hatchlings causes an increase
in number of captures of Sand Skinks from July through October
(with a particularly strong effect in August at ABS).
Though total monthly captures at ABS are higher in months with lower
precipitation and higher temperatures, this pattern is not present when
hatchlings are excluded from the analysis. Total monthly captures of Sand
Skinks at ONF show no relationship with temperature and precipitation.
182 Southeastern Naturalist Vol. 5, No. 1
Given that the significant relationship at ABS can be explained by the
presence of hatchlings in July through October, and data at ONF show no
association with temperature or precipitation, temperature and precipitation
do not have a direct effect on the number of captures of Sand Skinks
Daily surface activity, as indexed through tracks, depends on precipitation,
with more tracks detected on days with less precipitation. Precipitation
increases soil compaction, which may impede movement of Sand Skinks
through sand, causing less activity on days with rain. In fact, sand with >
27% moisture impedes movement of Sand Skinks (Lee 1969).
Daily activity does not depend on temperature, suggesting that environmental
conditions, at least at the southern portion of its range, permit
Sand Skinks to attain temperatures necessary for activity on most days
throughout the year. Indeed, in our study, Sand Skinks were found active
on days with maximum air temperatures as low as 20.6 °C, 8 to 12 °C
lower than selected body temperatures for Sand Skinks (Andrews 1994).
Activity at relatively low ambient temperatures may be facilitated by
fossoriality, because temperature profiles 5 mm into sand (Sand Skink
activity occurs just below the surface of sand) are higher, particularly
during mid-day, than air temperatures 1 mm above sand in open areas
(Andrews 1994). Even though we did not find a significant relationship
between activity per day and temperature, temperature does influence
daily activity cycles, with Sand Skinks showing unimodal activity (active
during the day) in January, but bimodal activity (activity mainly in the
evening and morning) in April and May (Andrews 1994).
In sum, activity of Sand Skinks is primarily influenced by precipitation
and reproductive activities. Unlike most tropical lizards (e.g., James 1994,
Lister and Aguayo 1992), the highest levels of Sand Skink activity do not
occur during times of greatest rainfall. In fact, activity is negatively associated
with rainfall. Instead, Sand Skinks show monthly activity patterns
similar to temperate zone species that breed in the spring (e.g., Fitch 1940,
Tinkle 1961). But unlike temperate zone species, temperature appears to
have less of an influence on Sand Skink activity than precipitation.
For access to museum specimens, we thank L. Ford (AMNH), J. Wiens (CM), A.
Resetar (FMNH), J. Simmons (KU), K. Beaman (LACM), J. Hanken (MCZ), A.
Braswell (NCSM), H. Dundee (TU), K. Krysko and M. Nickerson (UF), A. Kluge
(UMMZ), and K. de Queiroz (USNM). For permitting, we thank the Florida Fish and
Wildlife Conservation Commission (permits WX 01623, WX 97122). For weather
data, we thank N. Deyrup and M. Griffin. For funding, we thank Archbold Biological
Station, the Earthwatch Institute, USDA Forest Service, and US Fish and Wildlife
Service. For field assistance at ABS, we thank A. Knipps, B. Meneken, B.
Branciforte, and Earthwatch volunteers. For field assistance at ONF, we thank D.
Auth, L. Lowery, R. Lowery, M. Telford, and R.S. Telford. For comments and
discussion, we thank R. Andrews, M. Jennings, E. McCoy, P. Moler, H. Mushinsky,
K. Penney, and H. Swain.
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