Operating Body Temperatures in a Snake Community of
Northern Virginia
Carl H. Ernst, Terry R. Creque, John M. Orr, Traci D. Hartsell, and Arndt F. Laemmerzahl
Northeastern Naturalist, Volume 21, Issue 2 (2014): 247–258
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Northeastern Naturalist Vol. 21, No. 2
C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl
2014
247
2014 NORTHEASTERN NATURALIST 21(2):247–258
Operating Body Temperatures in a Snake Community of
Northern Virginia
Carl H. Ernst1,*, Terry R. Creque2, John M. Orr2, Traci D. Hartsell3,
and Arndt F. Laemmerzahl4
Abstract - Thermal data were collected from 15 of 16 species of snakes found at the Mason
Neck National Wildlife Refuge, Fairfax County, VA. Data recorded at each capture
included the date, 24-hour military time, body temperature (BT), air temperature (AT),
ground-surface temperature (ST), water temperature (WT) if in water, and the snake’s
activity (under cover, moving on land, basking, foraging, climbing, swimming, courting/
mating). The purpose of this study was to determine the potential range of operating body
temperature (OBT) of the individual species. The range of OBT is interpreted as the snake’s
operating temperature at its current environmental temperatures (ET), which can be used
in comparisons with similar data from other North American regions, and represents the
first such report from the Mid-Atlantic Region. The mean and ranges of BT, AT, ST, and
WT are presented for the eight snakes with 20 or more records: Carphophis amoenus (n =
238), Coluber constrictor (204), Nerodia sipedon (67), Thamnophis sirtalis (55), Diadophis
punctatus (54), Pantherophis alleghaniensis (43), Thamnophis sauritus (26), and Agkistrodon
contortrix (24). New thermal records are reported for several of these species. The
ranges of BT during activities are also reported. New temperature records are also reported
for Virginia valeriae (n = 16 encounters), Storeria dekayi (12), Opheodrys aestivus (6),
Lampropeltis calligaster (6), and Regina septemvittata (2).
Introduction
Ambient temperature plays a determining role in the behavioral, ecological and
social aspects of a reptile’s life (Bartholomew 1982, Cloudsley-Thompson 1971,
Huey 1982, Lillywhite 2001, Lueth 1941, Peterson et al. 1993). All reptiles are capable
of controlling their thermal environment through behavior, and in some cases
physiology. However, temperature still controls such physiological and ecological
life activities as feeding behavior and digestion, ecosystem and habitat selection,
movements (including seasonal migrations), and reproduction (sex cycles, mating
periods, and gestation and parturition periods). If environmental temperatures (ETs)
are either too cold or too hot, the reptile’s behavior and some physiological activities
are adversely affected and usually retarded. This relationship is particularly
true of elongated snakes, which have their body in contact with the ground. Because
of the great effect of ambient temperature (air, ground, water) on the behavior and
physiology of snakes, it is pertinent to study snakes’ occurrence within the ranges
1Division of Amphibians and Reptiles, mrc 162, Smithsonian Institution, PO Box 37012,
Washington, DC 20013-7012. 2Department of Environmental Science and Public Policy,
George Mason University, Fairfax, VA 22030. 3Homeland Security Investigations, 10720
Richmond Highway, Stop 5118, Lorton, VA 20598. 4Biology Program, George Mason University,
Fairfax, VA 22030. *Corresponding author - chernst@frontiernet.net.
Manuscript Editor: Todd Rimkus
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2014 Vol. 21, No. 2
of these temperatures. Such data not only help us to better understand the physiological
and reproductive nature of these animals, but also their ecological needs in
view of conservation.
The literature contains thermal data and studies of many species of snakes
(Avery 1982, Brattstrom 1965, Ernst and Ernst 2003, Lillywhite 2001). However,
studies of the thermal relationships between species and among individuals within
species of snakes are rare (Elick et al. 1980, Fitch 1956). From April 1982 through
August 2006, we studied such relationships within a snake community of 16 species
in northern Virginia (Agkistrodon contortrix (L.) [Copperhead], Carphophis
amoenus (Say) [Eastern Worm Snake], Coluber constrictor L. [Racer], Diadophis
punctatus (L.) [Ring-necked Snake], Heterodon platirhinos Latreille in Sonnini
and Latreille [Eastern Hog-nosed Snake], Lampropeltis calligaster (Harlan)
[Yellow-bellied Kingsnake], L. getula (L.) [Common Kingsnake], L. triangulum
(Lacépède) [Milk Snake], Nerodia sipedon (L.) [Northern Water Snake], Opheodrys
aestivus (L.) [Rough Green Snake], Pantherophis alleghaniensis (Holbrook)
[Rat Snake], Regina septemvittata (Say) [Queen Snake], Storeria dekayi (Holbrook)
[DeKay’s Brown Snake], Thamnophis sauritus (L.) [Common Ribbon
Snake], T. sirtalis (L.) [Common Garter Snake], and Virginia valeriae Baird and
Girard [Smooth Earth Snake]). The purpose of the study was to present data indicating
the normal range of cloacal body temperature (BT) of the snakes during
several common activities. These data can be considered the snake’s operating
body temperature (OBT) range at the site, and are the first reported for the Mid-
Atlantic Region that can be compared with such data from other North American
regions. A snake’s OBT, as used here, is interpreted as that BT it can achieve under
current climatic and meteorological conditions at the study site (Peterson et al.
1993); thus, it is a field temperature measurement only. OBT has been confused
and reported by researchers (Fitch 1960, 1965) as the preferred body temperature
(PBT). But PBT is best associated with the temperature selected by previously
conditioned snakes in a thermal gradient under controlled laboratory conditions
(Elick et al. 1980, Kitchell 1969, Landreth 1972, Lillywhite 2001), and as such is
not equivalent to a field measurement range of BT.
Materials and Methods
Field-site description
Collections were made at a 30-ha site on a peninsula jutting into the Potomac
River at the Mason Neck National Wildlife Refuge, Fairfax County, VA (38°67'N,
77°10'W; ≈25–35 m elevation); the site was restricted and closed to the general
public. The peninsula’s vegetation is composed primarily of upland hardwood
forest, predominantly oak (Quercus), but also includes an old wooded farmstead,
a >3-ha field undergoing succession, a brook with a ≈2-ha pond which flows
into a ≈5-ha tidal-freshwater marsh. The length of the peninsula is bisected by a
gravel road.
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Field materials and methods
Snake collections occurred from April 1982 to August 2006, but predominantly
from 1990 to 2006, and were conducted mostly during the prime annual
snake-activity period at this site (April through November; Ernst et al. 2012).
We employed 9 aged wooden boards and 14 abandoned sheets of roofing tin as
“cover boards” to provide shelter for snakes. Most data were derived from hand
collections because the use of drift fences was prohibited by Refuge policy. We
routinely examined natural hiding places (downed logs and rocks) and manmade
debris (old wood railroad ties, cinder blocks, sections of an old concrete sidewalk,
and a brick spring house).
Data collected from each snake included the snake’s behavior (separately moving
on land or in water, basking, foraging/feeding [ingesting], courting/mating, or
undercover/hibernating); maturity stage (male, female, or juvenile-immature based
on size at attainment of sexual maturity; Ernst and Ernst 2003); and total body
length (TBL) and tail length (TL) measured with a cloth measuring tape (large
snakes) or a standard metric ruler (small snakes). Snout–vent length (SVL) was
then calculated by subtracting TL from TBL. We recorded the mass of each snake
to the nearest 0.1 g with Pesola spring scales. Snakes heavier than 1000 g were
weighed with an ACCulab portable electronic balance of 4000-g capacity. We used
standard scale-clipping to mark all snakes for future identification (Brown and
Parker 1976) and did not count recapture data from the same date.
Body temperature was recorded cloacally with a Miller and Weber Schultheis
quick-reading thermometer accurate to 1 °C. We used gloved hands to handle
snakes to prevent transfer of heat from the collector, which might bias BT readings.
Corresponding air temperature (AT) and surface temperature (ST), or water
temperature (WT) if in water, were recorded at the time of capture and as close to
the position of original sighting as possible with a mercury thermometer accurate
to 1 °C; we also noted the date and 24-hour military time. After processing, snakes
were released at the point of capture. We considered snakes active if they responded
(moved) when handled. BT was not always measured because some snakes escaped
or were too small; we labeled such events as “observations” and recorded the AT,
ST, or WT.
Data analysis
Data were gathered over a relatively long period at different diel times, dates,
and meteorological conditions, and used to determine relationships between the
BT and the current ETs (AT, ST) and behavior of all eight species of snakes. The
correlation of BT to WT was only determined for Northern Water Snake, as no
other species had a large enough sample of swimming individuals. We performed
all statistical tests using R, Version 3.0.1, with alpha set at α = 0.05. However, we
adjusted alpha by dividing it in half because two correlations, AT and ST, were done
for each species, except for three for Northern Water Snake (AT, ST, and WT; α =
0.05/3).
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Results and Discussion
Correlations between the individual species’ BT and the ETs at the time of capture
are presented in Table 1 for those species captured and/or observed 20 or more,
and can be compared with like field data and laboratory studies involving thermal
gradients from other North American regional studies of snake thermal ecology
(summarized in Ernst and Ernst 2003). New BT, ST, and WT records are reported
for several Mason Neck snakes. The annual and daily activity cycles of Mason
Neck snakes has been previously reported by Ernst et al. (2012). Here, we recorded
environmental temperature and ancillary behavioral data for 15 of 16 snake species
present at the study site. A single juvenile Milk Snake was collected on 15 March
1999, but no temperature data were recorded.
In addition, new temperature records (*) were recorded for five snakes with fewer
than 20 encounters. Smooth Earth Snake (16 captures, 2 observations)—BT: range =
14.8–25.8* (mean = 20.5) °C, AT: range = 10.7*–23.0 (mean = 19.4*) °C, ST: range
Table 1. Relationships of cloacal body temperatures (BT) and environmental temperatures (AT = air
temperature, ST = substrate temperature, WT = water temperature) of snakes encountered more than
20 times at the Mason Neck National Wildlife Refuge. Correlation coefficients for BT vs. AT, ST, and
WT are given as r values. All temperatures in degrees Celsius. * = new record temperature
BT AT ST WT
Mean Mean Mean Mean
Species (n) (Range) (Range) (Range) (Range)
Carphophis amoenus (238) 23.1 22.3 19.9 -
(10.0–30.9) (10.4–31.9) (9.9–30.2)
r = 0.73 r = 0.76
Coluber constrictor (204) 28.1 17.9 24.6 -
(11.0–35.0) (11.5–36.4) (11.0–39.8)
r = 0.68 r = 0.72
Nerodia sipedon (67) 23.9 24.2 24.4 20.5
(14.4*–30.0) (14.4–33.0) (15.8–30.3) (13.6–27.8)
r = 0.71 r = 0.88 r = 0.93
Thamnophis sirtalis (55) 23.5 23.6 23.5 15.7*
(13.2–32.5) (14.1–31.6) (11.7–37.1*)
r = 0.87 r = 0.81
Diadophis punctatus (54) 18.6 20.3 18.1 -
(8.0–29.9) (10.0–28.0) (12.0–28.6)
r = 0.76 r = 0.84
Pantherophis alleghaniensis (43) 18.2 18.8 17.6 17.0*
(5.8*–32.2) (1.5–29.4) (5.7*–31.1*)
r = 0.91 r = 0.96
Thamnophis sauritus (26) 21.1* 23.3 23.0* 15.7
(14.0–32.5) (8.0–32.0) (8.0*–30.3)
r = 0.76 r = 0.90
Agkistrodon contortrix (24) 23.1 22.9 23.5 -
(16.0–30.5) (14.5–28.8) (16.0–31.0)
r = 0.91 r = 0.91
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= 11.0*–24.4* (mean = 17.9*) °C; Dekay’s Brown Snake (12 captures)—BT: range
= 14.8–30.8* (mean = 23.8) °C (C. Ernst [2003] reported temperature ranges for over
800 Dekay’s Brown Snakes in Lancaster County, PA, approximately 150 mi north
of Mason Neck: BT range = 10.0–29.5 °C, with 70% in the 20–27 °C range); Rough
Green Snake (6 captures, 1 arboreal observation)—AT: range = 22.9–27.5 (mean =
24.4*) °C, ST: range = 22.0*–29.0* (mean = 24.8*) °C; Yellow-bellied Kingsnake
(six hatchlings with yolk sacs found at nest with egg shells; 16 August 1982) – BT:
range = 25.9–26.2 (mean = 26.0) °C, AT = 30.0 °C, ST = 26.5* °C; and Queen Snake
(2 captures, basking)—BT = 24.0 and 29.0 °C, AT = 16.5* °C.
Species
Eastern Worm Snake (209 captures, 29 observations). Prior to some graduate
studies at Mason Neck (Creque 2001; Hartsell 1993; Orr 2003, 2006), nothing had
been reported about the thermal ecology of the Eastern Worm Snake. All previous
reports on the genus have concerned C. vermis (Western Worm Snake). Most Mason
Neck Eastern Worm Snakes spend the warmest months (July, August) underground.
We observed little surface activity (n = 2) for this species during this period. When
surface active, the species is almost exclusively nocturnal (Barbour et al. 1969).
Daylight hours were spent under cover (rocks, logs), resulting in the low mean BTs
reported (Table 1), which are comparable with similar reports for Western Worm
Snake (Clark 1967, 1970). Both species are secretive and not very tolerant of high
ambient temperatures. The behavioral thermal data gathered (Table 2) have not
been previously reported.
The range of OBTs for each snake activity (Table 2) varied with normal seasonal
ETs (lower in the spring and fall, higher in the warm summer months) and between
adults and immatures (juveniles, neonates/hatchlings). Sixty-eight percent of the
BTs of captured male Eastern Worm Snakes fell between 22 and 29 °C, and 50%
were in the range of 22–26 °C. Adult females had a similar peak (45%) between
23–26 °C, as also did immature individuals, 22–26 °C (50%). This is most likely
the OBT of Eastern Worm Snakes at Mason Neck.
Racer (157 captures, 47 observations). At Mason Neck, the Racer is entirely
diurnal (Ernst et al. 2012), and possibly because of its larger size is capable of
being surface active at higher ambient temperatures than the other snakes present
(Tables 1, 2). Its mean BT and highest AT, ST, and basking BT were all significantly
warmer than for the other species (P = 0.05). It was the only surface-active snake at
the refuge on extremely hot days, even at midday. Kitchell (1969) reported Racers
chose temperatures of 22.4–37.4 °C in a thermal gradient with a mean PBT of 31.5
°C, and the species is capable of experiencing BTs of 43–45 °C for a short period
(Bogert and Cowles 1947). In contrast to this, one found basking in this study had
a BT of 11.5 °C, the lowest recorded at Mason Neck for a basking snake. Fitch
(1963a) gave a BT range of 17–38 °C for hand-collected individuals, with most
records between 29–35 °C.
Most BTs records (60%) of mature male Racers were within the range 20–32
°C, but a second grouping (28%) of spring and fall records fell within the range
18–23 °C. Mature females had similar BT ranges of 28–32 °C (45%), and 21–26
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Table 2. Relationship of activity and cloacal body temperature (means and ranges °C) of snakes encountered more than 20 times at the Mason Neck Natural
Wildlife Refuge. * = new record temperature.
Cover Move Bask Forage Climb Swim Court
Mean Mean Mean Mean Mean Mean Mean
Species (n) (Range) (Range) (Range) (Range) (Range) (Range) (Range)
Carphophis amoenus (238) 22.6* 23.0* - - - - 25.1*
(10.0*–30.9*) (20.0*–26.0*) (23.1*–26.4*)
Coluber constrictor (204) 21.5 27.5 29.2 27.6 25.1 - 24.5
(12.0–30.0) (18.0–34.0) (11.5*–34.0) (22.0–30.4) (21.1–28.2) (15.0–35.0)
Nerodia sipedon (67) - 21.9 23.8 25.8 - 24.9 -
(20.0–23.8) (16.0–30.3) (23.8–27.8) (19.8–27.8)
Thamnophis sirtalis (55) 21.2 23.2 26.8* 31.0* 27.7* 19.6* -
(14.0–32.0*) (13.2–29.0) (20.0–32.5*)
Diadophis punctatus (53) 18.2 19.2 29.9 - - - -
(8.0–26.2)
Pantherophis alleghaniensis (43) 20.2 24.2 26.2 - 20.8 17.0 -
(5.8*–29.0) (19.0–32.2) (22.6–28.5)
Thamnophis sauritus (26) - 24.7 25.0* - 27.7* 19.6* -
(20.0–29.0) (14.0*–32.5*)
Agkistrodon contortrix (24) 24 27.8 21.3 - - - -
(21.0–25.0) (25.0–30.5) (16.0–27.0)
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°C (29%); 40% of female BTs were in the 17–26 °C range. Most combined adult
BTs (55%) were within the range of 26–32°C, and this appears to be the OBT range
for normal adult surface activity during the species’ most active annual period of
June–August. The Racer’s OBT range was the highest of the snakes at Mason Neck,
and matches the warm ETs during their most active months (Ernst et al. 2012).
Northern Water Snake (28 captures, 39 observations). All individuals were
found active and no more than 10 m from water. Most individuals close to water escaped
into deeper water when discovered, so temperature data are limited (Tables 1,
2). All data are comparable to those previously reported for the species (Ernst and
Ernst 2003). Sixty-nine percent of mature male Northern Water Snake BT records
fell between 23–26 °C. BTs of mature females occurred in two peak ranges: 20–26
°C (57%) and 28–31 °C (30%; all basking individuals). Eighty-nine percent of immature
BTs of swimming individuals were within the range of 19–24 °C. Fifty-two
percent of all Northern Water Snakes captured had BTs within 23–26°C, closely
matching the OBT range of most other snake species at Mason Neck. Lueth (1941)
reported the maximum temperatures selected in a thermal gradient were 36.5–43.0
°C. The minimum Northern Water Snake BT of 14.4 °C is slightly below the previously
reported range, but the ATs recorded were within the reported range. This
individual snake had probably just emerged from cooler water. Little or no data has
been previously correlated with activities of Northern Water Snakes (Table 2). No
hibernating Northern Water Snakes were found at Mason Neck.
Common Garter Snake (46 captures, 9 observations). The Common Garter
Snake is the most widely ranging snake in North America and the species that occurs
the farthest north. It is common in most regions, and its thermal ecology is
probably the best studied of North American snakes.
Common Garter Snake BTs of 0.5–35.0 °C for active individuals have been
reported, with most in the range of 25.0–29.0 °C; summer field BTs reported were
16.5–34.4 °C at ATs of 13.3–31.8 °C and STs of 14.5–33.4 °C (Ernst and Ernst
2003, Fitch 1965, Rossman et al. 1996). Common Garter Snake placed in laboratory
thermal gradients have chosen STs of 16.0–35.0 °C (Lueth 1941; Stewart 1965;
Kitchell 1969). Stewart (1965) reported the following differential sex ST preferences:
19.6–33.0 °C for males, 22.3–34.6 °C for nongravid females, and 21.2–33.7
°C for gravid females. The critical thermal maximum (CTmax) has been reported as
38.5–41.0 °C (Brattstrom 1965, Lueth 1941). Fitch (1956) found an apparently dying
wild Common Garter Snake with a BT of 40.5 °C.
The ranges of BTs and environmental temperatures recorded from free ranging
Mason Neck Common Garter Snakes (Table 1) are similar to those previously reported.
Unfortunately, few reported BTs have been correlated with snake activity other
than for surface-active, undercover, or hibernating individuals. Our BT/activity
correlations (Table 2) for moving and undercover Common Garter Snakes fit the reported
data well. The basking snakes we captured had a warmer range of BTs than
those previously reported (Fitch 1956), but some of the warmer reported BTs
may have been from basking snakes whose activity was not recorded. The only
reported BT of a swimming individual was 14 °C (Nelson and Gregory 2000); the BT
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of the only swimming Mason Neck Common Garter Snake collected was considerably
higher at 19.6 °C (WT 15.7 °C). A number of physiological laboratory studies
have shown that the Common Garter Snake is the most cold adapted of North American
snakes, especially those individuals from the more northernmost populations (for
a discussion and references of adaptations allowing this, see Ernst and Ernst 2003).
At Mason Neck, 60 percent of the BTs of male Common Garter Snakes were in
the range encompassing 22–27 °C, and 68% of female BTs were in this same range;
too few immature were captured to give a meaningful range estimate for that age
class. The OBT range for the species is apparently that of the two mature sexes,
22–27 °C.
Ring-necked Snake (47 captures, 7 observations). The Ring-necked Snake is another
predominately nocturnal species at Mason Neck; only two were found diurnally
surface active (Table 2). Reported BTs of Ring-necked Snakes have ranged from 0.0
°C to 34.4 °C (Brattstrom 1965, Ernst and Ernst 2003, Fitch 1975). The overall temperature
data recorded at Mason Neck fall within this range (Tables 1, 2).
In a laboratory thermal chamber, Ring-necked Snakes selected STs of 8–42
(mean = 34) °C, their maximum tolerated temperature was 37 °C, CTmax was 38 °C,
and mean habitat temperature was 25.5 °C (Elick et al. 1980). The species’ CTmin
and CTmax are probably 0 °C and 41 °C, respectively (Ernst and Ernst 2003). Because
the Ring-necked Snake seems to rarely bask and is usually found under cover
(often beneath tree bark), it probably most often thermoregulates through contact
with sun-warmed objects.
Most (69%) mature male Ring-necked Snakes at Mason Neck had BTs within the
range 20–26 °C, those of most mature females (50%) were within 21–25 °C, and
those of the majority (63%) of captured immature individuals were slightly cooler,
21–24 °C, but fell within the adult OBT range.
Rat Snake (31 captures, 12 observations). Some previous data are available for
the temperature relationships of Rat Snakes (Fitch 1963b, Landreth 1972). Reported
BTs of active individuals have been in the range of 18–38 °C, with most in
the range of 24–30 °C (Brattstrom 1965; Ernst and Ernst 2003; Fitch 1956, 1963b).
Overall, the majority (74%) of Rat Snake BTs recorded at Mason Neck fell between
16–30 °C (Table 1). A BT of 5.8 °C was recorded from three sluggish snakes at a
hibernaculum with an AT of 1.5 °C (see below). These temperatures are the lowest
so far reported for any Rat Snake responsive to touch; otherwise active Mason Neck
Rat Snakes had BTs within the range reported in the literature.
The BTs of adult male Rat Snakes fell between two ranges, 26–29 °C and 19–23
°C, which both had 29% of captures. Captured adult females had one major BT
range spanning 20–27 °C (54%). Seventy-nine percent of the BTs of captured immature
Rat Snakes were in the range of 17–20 °C, but most were found undercover.
The OBT of the Rat Snakes captured in the open at Mason Neck is probably in the
range of 22–29 °C.
Our Mason Neck data are valuable as neither ST nor WT correlations have
been previously reported for the species. Also, while some BTs and ATs have been
reported for Rat Snakes, few have been correlated with specific activities (Table 2).
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We have grouped and compared the temperatures of captured or observed snakes (all
showed some activity) into the categories of moving on the surface (7 captures, 7
observations), swimming (1), basking (5), under cover (8 captures, 3 observations),
and those at a hibernaculum (10 captures, 2 observations; the only hibernating species
found). Four of the movement records are of climbing snakes, though unfortunately
three of which were too high in trees to capture; ATs of 21.0–26.6 °C, STs
of 20.8–21.8 °C, and a single BT of 20.8 °C were recorded for the climbing snakes.
We assumed that the climbing snakes were either foraging for birds or squirrels.
The brick walls of an old spring house were used as a hibernaculum. Twelve
snakes (two too deep to capture) were found in various positions within crevices
during March of several years. They were apparently arising from hibernation and
all captured individuals responded to stimulation, although most were sluggish.
The mean BT of the 10 Rat Snakes captured at the hibernaculum was 8.4 (range =
5.8–23.8) °C; a BT of 23.8 °C was recorded from an animal that apparently had not
yet undergone spring emergence. The mean AT and ST of the 12 snakes encountered
at the spring house were 5.9 (range = 1.5–21.2) °C and 5.95 ( range = 5.7–21.2) °C,
respectively. If the high preemergence temperature is removed, the semi-dormant
snakes experienced the following temperatures: BT range = 5.8–12.0 (mean = 6.8)
°C, AT range = 1.5–16.8 (mean = 8.9) °C, and ST range = 5.7–16.1 (mean = 4.6)
°C. Weatherhead (1989) reported an approximate seven-month hibernation (October–
April) in Ontario with the snakes achieving BTs near 10 °C in January—higher
than recorded at Mason Neck, but the depth and description of the hibernaculum
were not given.
Common Ribbon Snake (18 captures, 8 observations). All Mason Neck Common
Ribbon Snakes were active when captured or observed (Tables 1, 2). Thermal data
recorded compares closely with the ranges reported elsewhere (Ernst and Ernst
2003, Rossman et al 1996), although the means for BT and ST are somewhat lower
because five of the 26 snake records were from active individuals in the cool month
of January. Carpenter (1956) found that 123 active Michigan Common Ribbon
Snakes had a mean BT of 26.0 (12.6–34.0) °C, with 70% falling between 20–30
°C, a mean AT of 22.28 (7–32) °C, and a mean ST of 26.23 (11–40) °C, with most
between 20–34 °C. Rosen (1991) reported a mean BT of 27.5 (19.0–33.4) °C for
Common Ribbon Snakes during the active season, and 30.0 °C during the middle
of clear warm days. The Common Ribbon Snakes he captured about the time of
entering or leaving hibernacula had a BT range of 12.0–32.2 °C; the BT means for
the males and females, respectively, were 25 and 23.5 °C. Rosen (1991) thought
the PBT for activity of these snakes to be about 30 °C as determined in controlled
laboratory studies.
Five Mason Neck Common Ribbon Snakes were observed on 5 January 1998,
an unseasonably warm day, basking on and around a large fallen tree beneath which
they had apparently been overwintering in rodent tunnels. Three escaped, but two
males captured had BTs of 26 °C and 29 °C at an AT of 22 °C (Hansknecht et al.
1999). On 22 March 2003, we captured two Common Ribbon Snakes which had
apparently just emerged from hibernation in a nearby decaying stump; the snakes
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2014 Vol. 21, No. 2
had BTs of 26.6 and 27.0 °C at an AT and ST of 21.6 and 22.0 °C, respectively. In
comparison, Carpenter (1953) recorded BTs of 5.4–5.8 °C for 11 yearling Michigan
Common Ribbon Snakes hibernating at depths of 20–38 cm in an ant mound.
Too few mature female or immature Mason Neck Common Ribbon Snakes were
captured to present meaningful OBT projections; however, 64% of the BTs of mature
males caught in the open were between 22–29 °C, and this is most likely the
species’ OBT range during the active season.
Copperhead (24 captures). The Copperhead is the only venomous snake at
Mason Neck, and past research elsewhere have yielded comparative temperature
data. Twenty-five active Kentucky Copperheads had BTs of 12–28 (mean = 20.0)
°C at ATs of 8–28 (mean = 21.9) °C, and STs of 8–31 (mean = 23.5) °C (Ernst and
Ernst 2011). Fitch (1956, 1960) thought that the species’ OBT in Kansas is between
26–28 °C. Clarke (1958) found other Kansas Copperheads active at ATs of 7.5–30.0
°C. Thus, the OBT range for activity is probably 23–31 °C for Kansas snakes. Sanders
and Jacob (1981) reported that summer BTs of Tennessee Copperheads varied
significantly according to snake SVL, and consequently thought the species’ CTmin
negatively correlated with SVL. Most Mason Neck Copperheads were captured
while undercover, but 50% of their BTs were in the range of 22–25 °C, a normal
OBT range for North American snakes.
The overall temperature data recorded for active Mason Neck Copperheads essentially
match those published previously, and most fall within the PBT range for
activity of 23–31 °C suggested for Kansas snakes by Fitch (1956, 1960), although
the mean BT of 23.1 °C of Mason Neck Copperheads was lower than that Fitch
(1960) referred to as the snake’s PBT. Fitch (1956) recorded a range of BTs of
17.5 and 34.5 °C for 39 found active in the open (AT range = 11.7–32.4 °C); BTs
of 67% of these snakes were within the range of 25.5–30.0 °C. BTs and ATs of the
two Mason Neck Copperheads found moving in the open (BT = 25.0 and 30.5 °C,
AT = 25.0 and 28.8 °C) fall within his ranges. Anderson (l965) reported that in
Missouri Copperheads remain stationary or crawl toward cover when found if ATs
are about 21 °C, , but become aggressive if the AT is about 27 °C, particularly in
the spring. Mason Neck Copperheads were aggressive at an AT of 18 °C.
The data presented in Tables 1 and 2 are only to show the snakes’ OBT ranges
during particular activities at a site in the Mid-Atlantic Region. Fifty-four percent
of all BTs of snakes captured were within the range of 20–26 °C, and we interpret
this as the OBT for normal snake activity at Mason Neck during the annual activity
season. Most of the temperatures recorded in Tables 1 and 2 fall between the ranges
reported previously (Avery 1982; Brattstrom 1965; Ernst and Ernst 2003, 2011).
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