OBSERVATIONS OF NOCTURNAL BASKING AND ACTIVITY IN SEVERAL AGAMID SPECIES.
Robert A. Valentic and Grant Turner.
Valentic, R.A. & Turner, G. 1998. Herpetofauna 28(1): 40-43.
Nocturnal activity and nocturnal basking have been reported in some species of Australian agamids which are otherwise known to be diurnal in habit. In particular these behaviours have been reported in the following species (denote A=active, B=basking, ?= not specified): Diporiphora sp. (A) and Tympanocryptis lineata (A) (Fyfe 1981), Amphibolurus nobbi (A), Ctenophorus fordi (A?) (Morley & Morley 1982), Pogona minor (A) and unidentified spp. (B) (Bush 1983), Diporiphora bilineata (A), Diporiphora magna (A) and Amphibolurus gilberti (A) (Bedford 1991), Pogona minor minor (B) (Orange 1992), Moloch horridus (A) (Niejalke 1994), Diporiphora bilineata (A), Amphibolurus gilberti (A) and Pogona vitticeps (A) (Valentic 1995), Ctenophorus caudicinctus (?) (Sonneman 1996). Thus to date nocturnal behaviour has been recorded in seven genera of Australian agamids suggesting it is more widespread than previously thought in this family. However the function of this behaviour is not always apparent and so there is a need to carefully document the circumstances under which observations take place, and where possible, the details of specimens involved.
We report on nocturnal behaviour in two gravid female Ctenophorus nuchalis lying on bitumen road surfaces at night and a single gravid female Tympanocryptis tetraporophora apparently active on a bitumen road at night. Some additional brief notes on nocturnal activity in Chlamydosaurus kingii, Tympanocryptis cephalus, C. nuchalis, C. cristatus and Diporiphora lalliae are also described.
The following abbreviations are used below: EST - eastern standard time, CST - central standard time, SVL - snout-vent-length, TL - tail length, from vent to tip, HL - head length, from tip of rostral scale to anterior edge of tympanum, HW - head width at mid-tympanum level. SVL and TL measurements were taken using a rigid 500mm ruler (1mm gradations) and head measurements using a vernier calliper accurate to 0.02mm.
At 20:44hrs (CST) on October 19th 1996 a suspected road-kill C. nuchalis was observed on the Tablelands Highway (136°00’E, 19°23’S) 44km north-east of the Barkly Homestead, central-eastern Northern Territory (NT). Weather was warm with clear skies, half-moon and a gentle breeze. Air temperature was 31.6°C, bitumen surface temperature was 32.3°C and relative humidity was 28%; the area had not received rain during the last few days. Habitat consisted of Acacia shrubland plain on compacting, red stony soils with numerous small termitaria. The sun had set at 18:44hrs (CST) that evening and it was dark when the observations occurred. Day-time weather was still, clear and sunny with a maximum temperature of 34°C. On closer inspection the specimen was observed lying prostrate to the bitumen with both eyes closed and was apparently uninjured. When touched the eyes opened, but otherwise the lizard remained motionless. On being picked-up it was very warm and began to struggle vigorously. It was a small female and was conspicuously gravid. Its dimensions were: SVL= 55mm, TL= 72mm, HL=13.3mm, HW=13.5mm. The specimen was retained for 24 hrs and closely inspected in order to ascertain that it had not been injured by a vehicle. The lizard had not been visible on the road surface at approximately 18:20hrs earlier in the evening, indicating that it had moved onto the road surface in between these times.
At 20:33hrs (CST) on the 22nd October 1996 a suspected road-kill C. nuchalis was observed on the access road to Poseidon Gold Pty Ltd mine (134°18'E, 19°14'S), 15.2km south-east of the Tennant Creek township (134°12'E, 19°38'S), central NT. This specimen was present on the road surface when traversed at approximately 19:45hrs (CST) earlier in the evening. Weather was warm with clear skies, half-moon and a gentle breeze. Air temperature was 33.0°C, bitumen surface temperature 33.5°C and relative humidity 28%; the area had not received rain during the past few days, although pools of water were present on some roadside verges and both Cyclorana australis and Litoria rubella were found active nearby. Habitat consisted of shrubland on a red, stony-soil plain with numerous small termitaria. The sun had set at 18:47hrs (CST) and it was dark when observations occurred. Day-time weather was still, clear and sunny with a maximum temperature of 35°C.
The specimen was observed lying prostrate against the bitumen with both eyes closed, apparently asleep. When the dorsal surface was touched the eyes opened but otherwise the lizard remained motionless despite us having driven over the top of it twice. On being picked-up it was very warm and began to struggle vigorously. It was a heavily gravid female. Its dimensions were: SVL=91mm, TL=114mm, HL=18.9mm, HW=18.8mm. It was closely inspected to ascertain that it had not been injured by a vehicle, although none were seen on this particular road during the evening.
At 19:05hrs (EST) on the 10th October 1996 an agamid was observed on the Landsborough Hwy (142°50’E, 22°08’S), 35km north-west of Winton (143°03’E, 22°23’ S) in central -western Queensland. The lizard had an alert, semi-upright stance with the tail arched, the anterior body and head lifted clear of the road surface; the groin and limbs were in contact with the surface. Weather was warm, with 40% cloud cover, no moon and a gusting easterly wind. Air temperature was 29.0°C, bitumen surface temperature 29.6°C and relative humidity 39%. Habitat consisted of Mitchell grass (Astrebla sp.) plain with dark brown, friable cavity-forming soils. The sun had set at 18:05hrs (EST) that evening and it was completely dark at the time the observation occurred. Day-time weather was sunny with a warm breeze and a maximum temperature of 37°C.
On closer inspection it was found to be a heavily gravid adult female T. tetraporophora. It attempted to flee on our approach, moving quickly to avoid being captured. On being secured (after about 20sec) it was noticeably warm. Its dimensions were: SVL=65mm,TL=91mm, HL=20.8mm, HW=14.64mm. There was little traffic on the road with no vehicles having traversed the highway at least 20min before the observation occurred.
In addition to these observations, G. Fyfe (pers. comm.) has observed basking and nocturnal activity in C. nuchalis and Diporiphora lalliae, M. Kearney (pers.comm.) has observed nocturnal activity in Ctenophorus cristatus while R. Pails (pers.comm) has observed nocturnal activity in Chlamydosaurus kingii and Tympanocryptis cephalus. The observations are described separately below:
Ctenophorus nuchalis: three adult C. nuchalis were observed lying prostrate on Larapinta Drive (Western MacDonnells road) between Alice Springs and the Hugh River in central-southern NT on different evenings and times of the year. Approximate times for each sighting were 20:30, 22:00 and 23:00hrs (CST). None of the lizards appeared to be injured. Hemipenes were manually everted in two of the specimens.
Diporiphora lalliae: More than three adult D. lalliae were observed in alert upright postures on a section of the Tablelands Hwy traversing the black-red soil intergrade habitat near Alroy Downs Stn, central-eastern NT. Observations occurred on a warm evening after 21:00hrs (CST). Roadside pools indicated recent rain and significant insect activity was noted.
Ctenophorus cristatus: At 21:15hrs (CST) on 27th January 1996 an active adult male C. cristatus was observed crouched on a dirt track cutting through mallee habitat on the Kimba Road in the Middleback Ranges, SA. Conditions were as follows: air temperature 20°C, relative humidity 66%, no rain, wind or cloud cover and half-moon.
Chlamydosaurus kingii: At approximately 21:30hrs (CST) on 12th January 1994 an adult female C. kingii was observed in an alert upright stance 1km east of the Stuart Hwy on the Edith Falls road (90km north of Katherine), NT. This bitumen road cuts through dry woodland. Weather was stormy with recent rainfall (early that evening) and day-time conditions were ‘hot’ (>30°C).
Tympanocryptis cephalus: Between 20:45-21:30hrs on 13th January 1994, five or six adult T. cephalus were observed in alert upright stances on the Orlando Mine road west of the Tennant Creek township in central NT. There was an approaching storm and the day-time conditions were warm and dry.
Climatic factors common to nearly all published reports of agamid nocturnal behaviour are high temperatures and the presence of moonlight. Usually the night-time conditions are described as ‘warm’ (>20°C) and/or preceding day-time conditions described as ‘hot’ (>30°C). Other possible influences such as rain or high relative humidity do not appear to be necessary precursors. The occurrence of gravid females on bitumen roads with temperatures above ambient air suggests that lizards were attempting to conduct heat from the road surface. This seems particularly likely in the case of C. nuchalis given their flattened postures. Similar postures appear to have been recorded by Bush (1983) who noted some agamids spotlighted at night as lying ‘belly down’ on granite or bitumen. Bedford & O’Grady (1996) described a peculiar ‘belly up’ posture in Tympanocryptis lineata lying on bitumen roads. We were not able to measure the body temperature of the lizards to ascertain whether their body temperatures were above ambient. It may also be significant that the majority of the observations of nocturnal basking/activity occurred in northern or central Australia (all except Bush 1983; Morley & Morley, 1982, Niejalke 1994, see Valentic 1995, Kearney- above) and that none occurred during the cooler/drier months of the year (from May through September). This would tend to emphasize the importance of temperature.
Nocturnal activity in some agamids has been observed to include foraging for insect debris on roads (Fyfe 1981, Bedford 1991, Valentic 1995, also see Bush 1983) and this cannot be ruled out in the case of the gravid T. tetraporophora for example. Niejalke (1994) suggests nocturnal sightings of agamids may result from either natural or human induced disturbance. We could not identify any extraordinary natural stimuli to account for our observations however it is always possible that approaching car headlights create the false impression of day-time, thus stimulating activity and possibly luring lizards onto road surfaces. This explanation does not account for the observations of C. nuchalis however and presumes that dragons can respond quickly to such stimuli.
While the bitumen temperatures we recorded were in each case above ambient air temperatures, the difference between the two were quite small (<1°C). Bedford & O’Grady (1996) in describing a peculiar belly-up posture in T. lineata doubted a thermoregulatory explanation of this behaviour, noting that the ground and air temperature ‘appeared similar‘ however differences of the magnitude we recorded would not be detectable unless measured. One cannot also discount the possibility that at the time the lizards moved onto the road surface the difference between the two was greater.
The question arises as to how long into the evening nocturnal basking and activity continues. In the case of C. nuchalis which is known to use burrows as nocturnal retreats, (as Amphibolurus inermis in Heatwole (1970) and Rankin (1977)) it would be of interest to know how their burrow temperature compares to road temperature and whether sleeping in the open increases their vulnerability to predation (see Sonnemann‘s (1996) observations of C. caudicinctus). There is also the more general question as to whether gravid female dragons spend more time basking than other conspecifics as is known to be the case in other, primarily viviparous, squamates (see Shine 1980).
We thank Greg Fyfe, Michael Kearney and Roy Pails for permitting us to include their observations in this work, Pete Matejcic of SAHG and Paul Reece of FNS South Australia for providing us with the references Niejalkie (1994) and Morley & Morley (1982). We also thank the referees for their helpful comments and improvements to the manuscript.
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