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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 Northeastern Naturalist 248 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 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. Northeastern Naturalist Vol. 21, No. 2 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 249 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). Northeastern Naturalist 250 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 Vol. 21, No. 2 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 Northeastern Naturalist Vol. 21, No. 2 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 251 = 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 Northeastern Naturalist 252 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 Vol. 21, No. 2 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) Northeastern Naturalist Vol. 21, No. 2 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 253 °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 Northeastern Naturalist 254 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 Vol. 21, No. 2 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). Northeastern Naturalist Vol. 21, No. 2 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 2014 255 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 Northeastern Naturalist 256 C.H. Ernst, T.R. Creque, J.M. Orr, T.D. Hartsell, and A.F. Laemmerzahl 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. 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