Behavioral Thermoregulation in Australian Elapid SnakesAuthor(s): Harvey B. LillywhiteSource: Copeia, Vol. 1980, No. 3 (Sep. 6, 1980), pp. 452-458Published by: American Society of Ichthyologists and HerpetologistsStable URL: http://www.jstor.org/stable/1444521Accessed: 29/06/2010 15:15

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Copeia, 1980(3), pp. 452-458

Behavioral Thermoregulation in Australian Elapid Snakes

HARVEY B. LILLYWHITE

Behavioral thermoregulation in laboratory thermal gradients was studied in seven species of Australian snakes of the Elapidae: Acanthophis antarcticus, Aus- trelaps superbus, Notechis scutatus, Pseudechis porphyriacus, Pseudonaja nuchalis, P. textilis and Unechis flagellum. All species exhibited well-developed thermoreg- ulatory behavior and controlled body temperatures with precision comparable to that reported for various heliothermic lizards. Temperature regulation is accom- plished by shuttling and by adjustments in the snake's position or orientation while basking. Thermal preferenda of the various species range roughly between 30 and 35 C and are similar to those of other terrestrial, Temperate Zone snakes in which thermal preferences have been adequately assessed. Thermal preferenda of adult snakes appear to be higher than those of newborn or juveniles (in four species) and may vary with levels of critical thermal minima (in five species) and geographic distribution.

NUMEROUS studies have demonstrated

the abilities of reptiles to maintain a char- acteristic range of body temperatures by pos- tural adjustments and the selection of appro- priate microenvironments (reviews by Cloud- sley-Thompson, 1971; Templeton, 1970; Brattstrom, 1965). In laboratory studies, ther- mal preferenda (Licht et al., 1966) may be de- scribed from analysis of behavioral responses to conditions which allow the opportunity for temperature regulation. These procedures are valuable in ascertaining the capabilities of rep- tiles for behavioral thermoregulation and in studying the levels and plasticity of thermal preferenda in relation to phylogenetic, ecolog- ical or physiological variables. Inherent thermal preferences may be important in limiting mi- crohabitat distribution and the timing of activ- ity (Huey and Slatkin, 1976), and may also un- derlie a suite of physiological adaptations to temperature (Dawson, 1975).

Although there exist numerous data on the thermoregulatory behavior of lizards, our knowledge of this subject in relation to other reptilian taxa is sparse and fragmentary. There has been strong interest in snake thermoregu- lation, but most studies have been limited to either of two families, the Colubridae and Boi- dae (Hammerson, 1977, 1979; Johnson, 1973; Dill, 1972; Webb and Heatwole, 1971; Osgood, 1970; Kitchell, 1969; Hutchison et al., 1966; Stewart, 1965; Cogger and Holmes, 1960). In the interest of extending our knowledge to oth-

er taxa of snakes, I sought to determine the thermoregulatory responses of seven species of Australian elapid snakes in laboratory thermal gradients.

MATERIALS AND METHODS

The snakes used in this study (Table 1) were collected in Victoria, South Australia and New South Wales, and were returned directly to the laboratory at Monash University. The snakes were maintained at 24-26 C in metal or wood cages with continuous access to water. Most snakes were tested in thermal gradients within one week of capture. Some of the snakes were held for 2-3 weeks and were fed mice during this period. However, these snakes were fasted for a minimum of four days prior to testing. All of the snakes selected for testing presum- ably were post-absorptive, appeared to be in a vigorous state of health and were not about to engage in skin-shedding.

Two enclosures were used for thermal gra- dients. Larger snakes (>60 cm total length) were tested in a metal cage 180 x 90 x 30 cm having a thick metal mesh top. Smaller snakes were tested in a wood cage 100 x 46 x 45 cm having a glass front and a screen mesh top. The floor of each cage was covered with dry soil overlain by a thin layer of dried grass clippings. Thermal gradients were established by posi- tioning a reflecting infrared heat lamp (250 watt red bulb) 30-45 cm above the substrate at

? 1980 by the American Society of Ichthyologists and Herpetologists

LILLYWHITE-SNAKE THERMOREGULATION 453

40o-

o

L35 -

w •- 30

- NOTECHIS SCUTATUS

PSEUDECHIS PORPHYRIACUS

- PSEUDONAJA TEXTILIS 25 I I I I

TIME, HOUR INTERVALS

Fig. 1. Telemetered body temperatures depicting thermoregulatory behavior of three different snakes. Examples were selected to illustrate variability and species differences. Note the early warm-up (by bask- ing) in all three individuals.

one end of each cage. The lowest temperature in the gradient was determined by ambient room air which usually ranged between 18 and 22 C. Body temperatures in excess of 40 C were possible if a snake was positioned directly be- neath the heat lamp.

Body temperatures of larger snakes were de- termined at intervals from a temperature trans- mitter positioned freely in the gut at mid-body.

Two types of transmitter were used. A short

range transmitter consisted of a squegging Hartley oscillator with an operating frequency of approximately 1 mHz on the AM broadcast band. A longer range, pulsed, crystal controlled citizen's band transmitter was sometimes used with an operating frequency of 27.24 mHz. Both types of transmitter emitted pulse rates dependent on temperature and were calibrated by use of a mercury thermometer and a con- trolled temperature bath. Each transmitter was coated with silicone before calibration and

feeding (forcibly) to a snake. The size of each transmitter with silicone was approximately 3 x 1.5 cm.

Each snake equipped with its transmitter was tested individually. A snake was introduced into the thermal gradient usually about 0700 h and observed at intervals thereafter. The snake's body temperature and position in the thermal

gradient were determined every 20 min (but sometimes shorter or longer intervals: see be- low) throughout the rest of the work day (end- ing at 1700-1800 h). Some snakes were ob- served (similarly) for 2-5 days.

Snakes smaller than 60 cm were tested in

TABLE 1. BODY TEMPERATURES OF SNAKES IN LABORATORY THERMAL GRADIENTS. The mean and range de- scribe all temperatures measured after each snake had first warmed (by basking) to its preferred or activity range of temperatures. Voluntary maxima are indicated as a single temperature or as a range of single

temperatures from different snakes.

No. No. measure-

Species animals ments X + SD Range Voluntary maxima Method

Acanthophis antarcticus 1 72 32.9 ? 3.64 27.2-38.5 38.5 telemetry

Austrelaps superbus

juveniles 2 38 31.0 ? 2.37 25.8-35.3 34.8-35.3 thermometer adults 4 78 32.8 ? 2.12 26.6-37.1 34.6-37.1 telemetry

Notechis scutatus

newborn 8 69 29.6 ? 2.66 23.0-34.0 34.0 thermometer adults 7 170 32.2 ? 1.58 25.9-35.5 32.2-35.5 telemetry

Pseudechis porphyriacus newborn 7 61 31.0 ? 1.90 27.0-35.0 35.0 thermometer adults 3 60 32.7 ? 1.70 28.1-36.3 33.7-36.3 telemetry

Pseudonaja nuchalis

juvenile 1 11 32.0 ? 1.01 30.2-33.8 33.8 thermometer adult 1 23 34.0 ? 1.21 31.8-36.9 36.9 telemetry

Pseudonaja textilis 2 36 34.5 ? 1.81 28.7-37.8 36.5-37.8 telemetry Unechis flagellum 3 51 30.1 ? 2.87 24.0-36.2 34.2-36.2 thermometer

454 COPEIA, 1980, NO. 3

TABLE 2. VARIABILITY OF THERMOREGULATION

AMONG INDIVIDUAL ADULT TIGER SNAKES, Notechis scu-

tatus. Temperatures were determined as in Table 1.

Body temperature, C Indi- Body vidual mass, g + SD Range

A* 380 33.0 ? 1.35 30.0-34.6 B* 300 31.5 ? 1.35 29.6-34.3 C 285 32.4 ? 1.20 29.7-34.3 D 200 30.7 ? 3.30 25.9-35.0 E 300 32.8 ? 1.36 30.2-35.0 F 296 30.4 ? 0.33 30.0-31.2 G 314 29.9 ? 4.16 23.8-35.5

* Gravid female.

thermal gradients without the use of transmit- ters. In these cases, the protocol was similar to that described for the larger snakes except that body temperatures were taken by a Schultheis thermometer inserted (orally) a few cm into the neck. Because of the disturbance to snakes, body temperatures were taken every hour or at longer intervals (1.5-3 h), and the period of measurements was protracted for several days. The smallest snakes (less than 30 cm total length) were tested in groups of 3-8 individu- als.

For purposes of correlating preferred tem- peratures with thermal tolerance, the critical thermal minimum (CTMin) was determined in twelve snakes. In these tests, a snake was cooled in chipped ice at a rate of about 1 C min-1 until immobilized. The criteria used to determine each snake's CTMin were 1) inability of the an- imal to right itself or to twist the body when turned ventral side up, and 2) the cessation of tongue flicks. The test was ended only when both of these conditions occurred. Tests for CTMin were conducted on snakes that had been held in the laboratory (24-26 C) for at least two weeks.

RESULTS

All of the snakes behaviorally regulated body temperature in the thermal gradients. Typical- ly, each snake elevated its body temperature by warming itself (basking) beneath the heat source and then maintained a relatively narrow range of elevated body temperatures during subsequent activity within the gradient (Fig. 1). Periods of movement generally included peri- odic sojourns to the warmer end of the thermal gradient, and periods of inactivity usually were

TABLE 3. CRITICAL THERMAL MINIMA DETERMINED

IN FIVE SPECIES OF ELAPID SNAKES.

Critical thermal Snake minimum, C

Austrelaps superbus A 1.0 B 0.1 C 1.8 a = 0.97

Notechis scutatus A 2.0 B 1.0 C 0.1 D 0.5 E 1.0 f = 0.92

Pseudechis porphyriacus A 3.0 B 3.0 I = 3.00

Pseudonaja nuchalis A 7.0 t = 7.25 Pseudonaja textilis A 7.5 = 7.25

spent near the heat source. All of the species exhibited thermal preferenda at or somewhat above 30 C (Table 1), although a broader range of body temperatures was tolerated. With one exception (see below), thermal preferenda of individual snakes differed little on different days, and there were no consistent trends in the daily differences. Control of body temperature was very precise in some individuals (F, Table 2). Smaller snakes appeared to maintain lower body temperatures than did larger snakes (Ta- ble 1), but these differences were not tested sta- tistically because the smaller snakes were un- marked in groups and the variance between or within individuals could not be distinguished. Differences in thermal preferenda were cor- related with differences in voluntary maxima (r = 0.577, P < 0.01, N = 23 observation pairs) and with levels of CTMin (Tables 1, 3).

During basking, snakes positioned their bod- ies in configurations which varied from out- stretched to tightly coiled. Adult specimens of Notechis scutatus, Pseudechis porphyriacus and Aus- trelaps superbus sometimes were observed at 5 or 10 min intervals and were seen to adjust bask- ing positions so as to vary the part of the snake which received the most heat (Fig. 2). It did not appear that (over time) any particular part of the body was warmed preferentially, and usu- ally all segments of the body length were posi- tioned to receive maximum heating at different times. Coil adjustments also were observed in the other species, but their temporal aspects were not noted in detail. Newborn snakes fre- quently formed aggregations near the heat source.

LILLYWHITE-SNAKE THERMOREGULATION 455

0910 0920 0930 27.1 31.2 32.2

Fig. 2. Sequence of body positions at ten minute intervals of an adult red-bellied blacksnake, Pseudechis porphyriacus, basking beneath an infrared heat lamp. The x represents the center of irradiance from the heat lamp, and the circle indicates roughly the iso- therm where irradiation is reduced to 50% of maxi- mum. Numbers indicate time and core temperature of the snake.

The single specimen of Acanthophis antarcticus was relatively sedentary, and its behavior dif- fered from that of the other species. This snake

usually remained in a stationary coil near the heat source, but occasionally changed the po- sition of its body as described above for N. scu- tatus, P. porphyriacus and A. superbus. I did not observe the nocturnal behavior of this snake, although on two occasions the heat lamp was left on overnight. Both times the snake was found near the heat lamp on the following morning and had a body temperature compa- rable to that which it maintained during the

daylight observation periods. On one occasion the heat lamp was positioned directly over the snake which allowed its body temperature to rise to 38.5 C before moving. Conversely, when the snake was lifted away from the lamp (two occasions), the animal returned to occupy a po- sition nearer the heat source. Body tempera- ture did not fall below 27.2 C during these ob- servations. Unlike individuals of other species, the mean preferred body temperature of A. antarcticus varied considerably on five different days (daily thermal preferenda = 36.3, 29.4, 29.7, 33.6, 31.3 C).

Unechis flagellum is a secretive species, and the specimens studied remained concealed beneath a dense layer of dried grass clippings which covered the cage floor. These snakes clearly thermoregulated and usually were found near the heat source, but their movements and be- havior were not observed.

DISCUSSION

Thermoregulatory behavior is well devel- oped in all of the snakes which were studied

and is comparable in pattern and precision to that reported for various heliothermic lizards. Thermal preferenda of the seven species range roughly between 30 and 35 C and are (gener- ally) similar to preferred temperatures report- ed for other terrestrial, Temperate Zone snakes in which thermal preferences have been stud- ied adequately (Hammerson 1977, 1979; Moore, 1978; Jacobson and Whitford, 1971; Platt, 1969). There is considerable convergence of thermoregulation between Australian brown snakes (Pseudonaja) and the colubrid Masticophis studied by Hammerson (1977, 1979). Both gen- era are characterized by relatively high thermal

preferenda, similar behavior in a thermal gra- dient and generally comparable precision and consistency of body temperature control. These snakes are taxonomically and geographically distant, but are similar ecologically in that both are swiftly-moving diurnal animals which feed on small rodents and other reptiles sometimes in xeric habitats. Hence, this example suggests that predictable adaptive patterns of thermo- regulatory behavior have evolved among snakes.

The nocturnal snakes A. antarcticus and U. flagellum regulated body temperature in pho- tothermal gradients but with less consistency than was observed in the other species. This difference possibly was evoked by the testing procedure which was not entirely appropriate for nocturnal or secretive snakes.

There is very little information on the body temperatures of elapid snakes under natural conditions. Heatwole (1976; Heatwole and Johnson, 1979) reported ranges of 25.0-33.8 and 27.2-33.2 C for naturally active N. scutatus and P. porphyriacus, respectively, and these tem- peratures correspond reasonably well with the range and preferenda of body temperatures determined in the laboratory (Table 1). Ham- merson (1979) found that body temperatures of Masticophis in thermal gradients were very similar to those obtained in outdoor enclosures under a variety of weather conditions. My data for laboratory thermal preferenda differ only a little from independent assessments by Geof- frey Witten (pers. comm.) who determined a thermal preferendum of 33.8 C for P. porphy- riacus; those of four other diurnal elapid species, including N. scutatus and A. superbus, were ca. 31 C.

The behaviors of snakes altered both the di- rection of heat exchange (e.g., basking) and the rate at which body temperatures changed (pos-

456 COPEIA, 1980, NO. 3

ture or orientation). Coarse body temperature control was achieved principally by shuttling between the heat source and other parts of the thermal gradient, while adjustments in posture and orientation during basking permitted finer control of body temperature and probably min- imized horizontal temperature gradients within the snake. The dynamics of orientation behav- iors observed in basking snakes (Fig. 2) impli- cate a role of peripheral thermal receptors (Ca- banac and Hammel, 1971) in regulating heat uptake over the whole body and provide the inference that body temperatures were rela- tively uniform. Heatwole and Johnson (1979) observed flattening and tilting in cold red-bel- lied blacksnakes, P. porphyriacus, basking in sunlight. They concluded that posture is a ma- jor influence on the rate of change of core tem- perature and suggested that horizontal gradi- ents are more important than are vertical ones in influencing the heating and cooling of the body. I did not observe pronounced flattening by snakes, but the snakes I observed were never as cold as those studied by Heatwole and John- son. Several reports have emphasized the ap- parent tendencies of certain snakes to selective- ly heat different parts of the body and to maintain thermal gradients within body tissue (Hammerson, 1977; Johnson, 1973; Webb and Heatwole, 1971; Regal, 1966; Benedict, 1932). I did not have the capability to monitor regional body temperatures from snakes during the present investigations; however, the shifting behavior of these snakes while basking (Fig. 2) probably eliminated appreciable thermal gra- dients within their bodies.

Little attention has been paid to possible changes in thermal preferenda during the on- togeny of reptiles. In the present study, mean preferred body temperatures of newborn orju- venile snakes were lower than those of adults of the same species (Table 1). This possibly in- dicates an ontogenetic difference in thermal choice, but alternative interpretations come to mind. First, it is possible that in the newborn of N. scutatus and P. porphyriacus the tendency to aggregate interfered with thermoregulatory behavior, although I did not observe anything to indicate that thermoregulation was socially inhibited as reported for some lizards (Regal, 1971). Second, body temperatures of small snakes were taken at intervals with a thermom- eter whereas body temperatures of larger snakes were obtained from radio transmitters positioned in the gut. If indeed head-body tem-

perature differences were maintained by these snakes, these differences might be reflected by thermometer placement. The Schultheis meth- od perhaps comes closer to measuring head temperatures than does the transmitter meth- od. It is further conceivable that the mere pres- ence of an object in the gut causes the heat seeking behavior reported to occur in certain snakes and other ectothermic vertebrates (Lang, 1979; Witten and Heatwole, 1978; Re- gal, 1966; Cogger, 1974; Gatten, 1974; Lilly- white et al., 1973). Digestion in various other snakes (Hammerson, 1979; Kitchell, 1969) and crocodilians (Diefenbach, 1975) is not accom- panied by any significant upward shift in the mean body temperature when compared with fasted animals. In those snakes and crocodilians which show a thermophilic response following feeding, the elevation of body temperature above fasting levels is proportionate to the vol- ume or mass of ingested food (Saint Girons, 1975; Lang, 1979). The size of the transmitter used in the present study was relatively small and did not noticeably distend the gut. More- over, experiments with toads indicated that the elevation in preferred body temperature fol- lowing meal ingestion cannot be attributed sole- ly to the mechanical stimulus of objects in the gut (Lillywhite et al., 1973).

Pough and Busack (1978) reported that sub- adult Spanish fringe-toed lizards, Acanthodacty- lus erythrurus, maintained a significantly lower mean body temperature (35.4 C) than adults (38.3 C) in the field. The activity of subadults is curtailed by high temperatures during three months of summer while the activity of the more thermophilic adults is curtailed only dur- ing July and August. The possibility that young snakes have a thermal preferendum lower than that of adults is consistent with certain obser- vations from ecological studies. Young colubrid snakes may be active later in the year than are adults of the same species (Brown and Parker, 1976) and probably are less active than the adults during the active season (Lillywhite, in press). Possibly during these periods small snakes are operating at lower body tempera- tures than those which characterize the active adults. Unfortunately, very little information is available concerning ecological differences be- tween different age classes of elapid or other snakes.

Laboratory thermal preferenda are generally correlated with cold tolerance (as measured by CTMin) in five species of elapid snakes for

LILLYWHITE-SNAKE THERMOREGULATION 457

which both measurements are available (Tables 1, 2). Hence, both species of Pseudonaja dem- onstrated the highest CTMin and also selected high body temperatures in thermal gradients. Lower CTMin and selected temperatures char- acterized N. scutatus and A. superbus, with P. por- phyriacus being intermediate. The species hav- ing the lower CTMin (better cold tolerance) are restricted to a southerly distribution in Austra- lia, whereas the other species range much far- ther north. The two species of Pseudonaja both occur in open, dry and sometimes hot environ- ments. My data are corroborated crudely by those of Heatwole (1976) who reported CTMin of N. scutatus to be lower than that of P. textilis, but that of A. superbus only slightly lower than that given for Pseudonaja. These data indicate that attributes of thermal physiology are ad- justed in relation to levels of preferred body temperatures or vice versa.

ACKNOWLEDGMENTS

I am indebted to A. K. Lee for the use of his laboratory and to the Department of Zoology, Monash University, for support during my stay as a visiting scientist. Special thanks are extend- ed to Ron Waters and Roger Martin who pro- vided some of the snakes.

LITERATURE CITED

BENEDICT, F. G. 1932. The physiology of large rep- tiles with special reference to the heat production of snakes, tortoises, lizards and alligators. Carnegie Inst. Wash. Publ. No. 425, Washington, D.C.

BRATTSTROM, B. H. 1965. Body temperatures of reptiles. Amer. Midl. Nat. 73:376-422.

BROWN, W. S., AND W. S. PARKER. 1976. Movement ecology of Coluber constrictor near communal hiber- nacula. Copeia 1976:225-242.

CABANAC, H. P., AND H. T. HAMMEL. 1971. Periph- eral sensitivity and temperature regulation in Tili- qua scincoides. Internat. J. Biometeor. 15:239-243.

CLOUDSLEY-THOMPSON, J. L. 1971. The temperature and water relations of reptiles. Merrow Publ. Co., Watford Herts.

COGGER, H. G. 1974. Thermal relations of the mal- lee dragon Amphibolurus fordi (Lacertilia: Agami- dae). Aust. J. Zool. 22:319-339.

. 1975. Reptiles and amphibians of Australia. A. H. & A. W. Reed, Sydney.

, AND A. HOLMES. 1960. Thermoregulatory behavior in a specimen of Morelia spilotes variegata Gray (Serpentes:Boidae). Proc. Linn. Soc. New South Wales 85:328-333.

DAWSON, W. R. 1975. On the physiological signifi-

cance of the preferred body temperatures of rep- tiles, p. 433-473. In: Perspectives of biophysical ecology, ecological studies. Vol. 12. D. M. Gates and R. B. Schmerl (eds.). Springer-Verlag, N.Y.

DILL, C. D. 1972. Reptilian core temperatures: vari- ation within individuals. Copeia 1972:577-579.

DIEFENBACH, C. 0. 1975. Thermal preferences and thermoregulation in Caiman crocodilus. Copeia 1975:530-540.

GATTEN, R. E., JR. 1974. Effect of nutritional status on the preferred body temperature of the turtles Pseudemys scripta and Terrapene ornata. Copeia 1974:912-917.

HAMMERSON, G. A. 1977. Head-body temperature differences monitored by telemetry in the snake Masticophis flagellum piceus. Comp. Biochem. Phys- iol. 57A:399-402.

- . 1979. Thermal ecology of the striped racer, Masticophis lateralis (Serpentes: Colubridae). Her- petologica 35:267-273.

HEATWOLE, H. 1976. Reptile ecology. Univ. Queens- land Press, St. Lucia.

- , AND C. R. JOHNSON. 1979. Thermoregula- tion in the red-bellied blacksnake, Pseudechis por- phyriacus (Elapidae). Zool. J. Linn. Soc. 65:83-101.

HUEY, R. B., AND M. SLATKIN. 1976. Costs and ben- efits of lizard thermoregulation. Quart. Rev. Biol. 51:363-384.

HUTCHISON, V. H., H. G. DOWLING AND A. VINE- GAR. 1966. Thermoregulation in a brooding fe- male Indian python, Python molurus bivittatus. Sci- ence 151:694-696.

JACOBSON, E. R., AND W. G. WHITFORD. 1971. Phys- iological responses to temperature in the patch- nosed snake, Salvadora hexalepis. Herpetologica 27:289-295.

JOHNSON, C. R. 1973. Thermoregulation in py- thons---II. Headbody temperature differences and thermal preferenda in Australian pythons. Comp. Biochem. Physiol. 45A:1065-1087.

KITCHELL, J. F. 1969. Thermophilic and thermo- phobic responses of snakes in a thermal gradient. Copeia 1969:189-191.

LANG, J. W. 1979. Thermophilic response of the American alligator and the American crocodile to feeding. Copeia 1979:48-59.

LICHT, P., W. R. DAWSON, V. H. SHOEMAKER AND A. R. MAIN. 1966. Observations on the thermal re- lations of Western Australian lizards. Copeia 1966:97-110.

LILLYWHITE, H. B. 1980. Tracking as an aid in the study of snake communities. In: Herpetological communities: A Symposium of the Society for the Study of Reptiles and Amphibians and the Her- petologist's League, August 1977. N. J. Scott (ed.). Assoc. Syst. Curators, Lawrence, Kansas. In press.

~- , P. LICHT AND P. CHELGREN. 1973. The role of behavioral thermoregulation in the growth en- ergetics of the toad, Bufo boreas. Ecology 54:375- 383.

458 COPEIA, 1980, NO. 3

MOORE, R. G. 1978. Seasonal and daily activity pat- terns and thermoregulation in the southwestern

speckled rattlesnake (Crotalus mitchelli pyrrhus) and the Colorado desert sidewinder (Crotalus cerastes la- terorepens) Copeia 1978:439-442.

OSGOOD, D. W. 1970. Thermoregulation in water snakes studied by telemetry. Copeia 1970:568-571.

PLATT, D. R. 1969. Natural history of the hognose snakes Heterodon platyrhinos and Heterodon nasicus. Univ. Kans. Publ. Mus. Nat. Hist. 18:253-420.

POUGH, F. H., AND S. D. BUSACK. 1978. Metabolism and activity of the Spanish fringe-toed lizard (Lac- ertidae: Acanthodactylus erythrurus). J. Thermal Biol. 3:203-205.

REGAL, P. J. 1966. Thermophilic response following feeding in certain reptiles. Copeia 1966:588-590.

. 1971. Long term studies with operant con-

ditioning techniques, of temperature regulation patterns in reptiles. J. Physiol. 63:403-406.

SAINT GIRONS, H. 1975. Observations preliminaires

sur la thermoregulation des viperes d'Europe. Vie Milieu Ser. C, Biol. Terr. 25:137-168.

STEWART, G. R. 1965. Thermal ecology of the garter snakes Thamnophis sirtalis concinnus (Hallowell) and Thamnophis ordinoides (Baird and Girard). Herpe- tologica 21:81-102.

TEMPLETON, J. R. 1970. Reptiles, p. 167-221. In:

Comparative physiology of thermoregulation, vol. 1. G. C. Whittow (ed.). Academic Press, New York.

WEBB, G., AND H. HEATWOLE. 1971. Patterns of heat distribution within the bodies of some Australian

pythons. Copeia 1971:209-220. WITTEN, G. J., AND H. HEATWOLE. 1978. Preferred

temperature of the agamid lizard Amphibolurus nob- bi nobbi. Copeia 1978:362-364.

DEPARTMENT OF PHYSIOLOGY AND CELL BIOLO-

GY, UNIVERSITY OF KANSAS, LAWRENCE, KAN-

SAS 66045. Accepted 22 May 1979.

Copeia, 1980(3), pp. 458-462

Orientation to the Sun by the Iguanid Lizards Uta stansburiana and Sceloporus undulatus: Hourly and Monthly Variations

STEVE WALDSCHMIDT

Populations of Uta stansburiana and of Sceloporus undulatus were studied in western Colorado. The distribution of the behavioral responses of these lizards within four orientational categories showed significant variations throughout the summer. These variations were closely associated with both monthly and hourly changes in the thermal environment. During the day, the percentage of lizards found in the shade was positively associated with increasing air temperature. The observed frequencies of lizards in both parallel and perpendicular orientations to the sun's rays suggest that these orientations are important behavioral re-

sponses to the thermal environment in the early morning and late afternoon.

AN ectotherm can regulate its body temper- ature by selecting different microhabitats,

altering its activity periods, and changing its body surface areas that are exposed to thermal fluxes. Many studies have shown that lizards are capable of modifying their energy (heat) bal- ance and thus behaviorally regulating their body temperature [see reviews by Brattstrom (1965) and Huey and Slatkin (1976)].

For two lizard species, I show that the relative frequencies of four behavioral categories change daily and monthly throughout the sum- mer. I hypothesize that these behavior patterns

are thermoregulatory, and are used to alter the body surface area exposed to direct solar ra- diation. If other factors that affect the energy balance of a lizard are held constant, changes in surface area will affect a lizard's body tem- perature by altering the amount of direct solar radiation absorbed (Bartlett and Gates, 1967; Porter et al., 1973; Muth, 1977).

MATERIALS AND METHODS

Study site.-The 1,200 m2 study site was lo- cated on a south facing hillside (1,658 m ele-

@ 1980 by the American Society of Ichthyologists and Herpetologists