Herpetological articles
Notes on the occurrence and habits of the Downs Bearded Dragon Pogona henrylawsoni (Wells & Wellington, 1985).
Grant Turner and Rob Valentic.
Turner, G. & Valentic, R.A. 1998 (a). Herpetofauna 28(1): 12-18.
INTRODUCTION
Pogona henrylawsoni is a medium sized Pogona confined to the black-soil plains region of central and western Queensland, from Gregory Downs to Longreach and Aramac (Witten 1994a, Shea 1995). The species has had a somewhat unstable taxonomic history. It was originally described by Wells & Wellington (1985) as Pogona henrylawsoni in their taxonomic revision of the Australian herpetofauna. Following (unsuccessful) moves to have this work suppressed (ASK 1987, ICZN 1991), the species and species name, failed to gain acceptance by most authors. The species was present in live captive collections since the early 1970’s in both the USA and Germany where it was known as Amphibolurus ‘rankini’. It was only briefly referred to in books by Wilson & Knowles (1988) and Ehmann (1992), and treated as an undescribed species in both; it was not referred to in Cogger (1986, 1992). Witten (1994a) described the species as P. brevis on account of a failure to locate the holotype and the claimed inadequacy of the Wells & Wellington (1985) diagnosis of P. henrylawsoni. Shea (1995) subsequently claimed these actions were invalid and proposed the retention of the original name (P. henrylawsoni) on the grounds of stability.
There is currently little information available on the natural history of the downs bearded dragon, Pogona henrylawsoni. In Wilson & Knowles (1988) the photographed specimen came from Winton, Qld with the comment “moderately small very robust Pogona with poorly developed ‘beard’. Apparently restricted to deeply cracking clay soils (black-soil plains) in interior of Qld” (p.220). Ehmann (1992, p.138) referred to it as the black-soil bearded dragon (Pogona sp.) and provided a brief description and comment on its escape behaviour. Greer (1989, p.13) referred to the species as ‘P. henrylawsoni’ but no information was presented on the species’ biology. The species has been successfully maintained in some USA and German collections for more than 20 years where it has been repeatedly bred (Michl 1986-7, de Vosjoli & Mailloux 1993, p.47, 1996); it has also been bred at Melbourne Zoo (see Witten 1994b).
Our observations of P. henrylawsoni relate to a brief excursion through the black-soil plains region of central-west Queensland in October 1996. During the afternoon of October 10 and the morning of October 11 we were able to make a series of observations on P. henrylawsoni as we travelled along the Landsborough Hwy between Longreach (144°15’E, 23°26’S) and McKinley (141°17’E, 21°17’S), passing through the towns of Morella (143°52’E, 28°58’S), Winton (143°03’E, 22°23’S) and Kynuna (141°55’E, 21°35’S) along the way.
OBSERVATION
A total of 14 P. henrylawsoni were sighted and of these nine were captured. Locality data and the circumstances, conditions, etc. surrounding the sightings of each lizard are presented in Table 1. Measurements and descriptions of seven of these lizards were taken and data are presented in Table 2. Measurements were performed with a rigid 500mm ruler (accurate to 1mm), vernier calliper (accurate to 0.02mm) and spring balance (accurate to 2g).
Table 1 Locality data and observations relating to each of the P. henrylawsoni sightings. Quoted temperatures refer to air temperatures in the shade, RH denotes the relative humidity and time is EST. Locality data are given relative to the Winton township (143°03’E, 22°23’S).
No. Date-Time Conditions Location
1 10/10/96 - 4:56pm Full sun 37.4°C; RH 31% 77.5km SE of Winton, Qld
Prostrate on bitumen surface. Adult. Landsborough Hwy.
2 - 5:03pm Full sun 37.0°C; RH 31% 69.2km SE of Winton, Qld
Basking on rock 15m from road. Adult. Landsborough Hwy.
3 - 5:09pm Full sun 37.0°C; RH 31% 62.1km SE of Winton, Qld
Basking on rock 10m from road. Adult Landsborough Hwy.
4 - 5:16pm Full sun 37.2°C; RH 31% 53.5km SE of Winton, Qld
Basking on a rock 20m from road. Adult. Landsborough Hwy.
5 - 5:20pm Full sun 37.0°C; RH 31% 50.2km SE of Winton, Qld
Basking on a rock 15m from road. Adult. Landsborough Hwy.
6 - 5:51pm Full sun 37.0°C; RH 31% 13.0km SE of Winton, Qld
Basking on a rock 15m from road. Adult. Landsborough Hwy.
7 - 6:42pm Roadkill approx. 1 week old. Adult 47km NW of Winton, Qld.
Landsborough Hwy.
8 11/10/96 - 9:42am Overcast 29.0°C; RH 42% 52.4km NW of Winton, Qld
Perched on rock 15m from road. Landsborough Hwy.
Ground temp 42.3°C. Adult
9 - 10:01am Partial sun 30.1°C; RH 38% 54.2km NW of Winton, Qld
Perched on rock; retreated down natural Landsborough Hwy.
crevice. Adult.
10 - 10:27am Full sun 31.8°C; RH 37% 62.3km NW of Winton, Qld
Basking on rock; retreated down natural Landsborough Hwy.
crevice next to rock. Adult.
11 - 10:36am Full sun 35.0°C; RH 32% 66.1km NW of Winton, Qld
Basking on rock; retreated down natural Landsborough Hwy.
crevice next to rock. Adult.
12 - 10:39am Full sun 35.0°C; RH 32% 68.0km NW of Winton, Qld
Basking on rock; attempted to retreat down Landsborough Hwy.
natural crevice 0.5m from rock.
Rock surface temp 37.4°C. Adult.
13 - 11:34am Full sun 36.8°C; RH 31% 111.9km NW of Winton, Qld
Propped against small shrub on road edge Landsborough Hwy.
Adult.
14 - 12.28pm Full sun 38.9°C; RH 31% 170.6km NW of Winton, Qld
Perched on a vertical branch of dead shrub; Landsborough Hwy.
Attempted to retreat down burrow. Adult.
Habitat: The black-soil plains of the region are sparsely vegetated. The tree-layer is entirely lacking and shrubs where they occur are sparse. While the region is known to support various grasses (notably Mitchell Grass, Astrebla sp.) at the time of our visit the area was in drought and these were almost entirely lacking, leaving the soil exposed. The soil is dark brown in colour, crumbling and friable (to the extent that one leaves distinct indentations walking on it). They form numerous deep cracks and labyrinthine cavities. The roadside strip (10-30m wide strip between the road edge and fence) was almost entirely devoid of vegetation (see Figure 1). Small rounded rocks (<0.5m diameter) were common in the strip but are generally uncommon beyond the fence line suggesting that they were excavated during road construction. Wooden fence posts were typically quite narrow (<10cm) and of uniform size and shape.
Size & Description: Length measurements of seven P. henrylawsoni are given in Table 2. Witten (1994a) records mature adult P. henrylawsoni as having the following average SVL's: Males- SVL=128mm (range 91-148mm, n=5) and Females- SVL=130.8mm (range 122-138mm, n=3). Most of the females in Table 2 fall outside this range; the significance of this is not clear. The species may be smaller in the Winton area or drought conditions may have prevented full adult size being attained. By comparison measurements of ‘breeding’ adults in de Vosjoli & Maillouz (1993, p.47, n=?) exhibited the following ranges: Males-SVL=124-146mm, Total L= 254-305mm and Females- SVL=127-152mm, Total L= 230-286mm. All but one of the SVL measurements given in Table 2 lie outside the combined SVL range 124-152mm, however all except one specimen (#13, with a truncated tail) had total lengths (SVL+TL) within their stated range. Ehmann (1992) gives head & body length ‘to 13cm’ and a total length of 25cm consistent with above. In Shea (1995) holotype measurements of P. henrylawsoni were SVL=126mm, TL=116mm and measurements of several Australian Museum specimens are given as SVL=120, 117mm. In Table 2 all specimens in which the tail was complete, TL exceeded SVL and this was also noted by Witten (1994a). None of the other specimens observed were substantially larger or smaller than those in Table 2. No specimens which could be classed as ‘sub adult’ or ‘juvenile' were seen. We were unable to locate any published data on the mass of adult P. henrylawsoni for comparison with our data.
A general colour and pattern description is based on the nine captured lizards. Specimens were all grey-brown dorsally with five or six pale grey paravertebral blotches, which in some individuals coalesce on the midline. The tail has between 13-19 dark brown bands, which may be either distinct or indistinct. Some had a dark pinkish-brown flush on the gular region. Ventral surface was white with a grey-brown variegated pattern. The buccal cavity was lemon yellow to orange, with the tongue usually bright orange (see Wells & Wellington 1985). Iris colour was typically gold sometimes with a red-brown infusion. As with other Pogona species, P. henrylawsoni is capable of marked, rapid colour changes. This was particularly evident in specimen #13 whose ventral surface changed from clean white to having a conspicuous superposed grey-brown variegated pattern within 5 minutes of capture; the gular region was also initially white and turned grey in this time. Specimens #1, 2 and 3 were dorsally yellow-brown on capture; by the next morning they were a drab grey-brown. Preanal pores numbered two (1L:1R) in all specimens while femoral pores numbered either four (2L:2R, n=5) or six (3L:3R, n=4). These fall within the stated range of 6-12 (mean 8.18) in Witten (1994a).
Sexing P. henrylawsoni proved difficult and the sexes assigned to individuals in Table 2 are tentative. None of the lizards examined had palpable eggs or enlarged ova. Wells & Wellington (1985) report ovigerous females in January while northern hemisphere captives oviposit from March to June (de Vosjoli & Mailloux 1993). There were no obvious post-anal pouches indicating the presence of swollen hemipenes in males. None of the specimens had the appearance of having recently deposited eggs (e.g., ‘hollow’ abdominal region) and the mass of individuals was fairly consistent (Table 2).
P. vitticeps is known to occur sympatrically with P. henrylawsoni in the Aramac region (Witten, pers.comm.) though we did not observe any lizards fitting the description of the former. P. henrylawsoni is distinguished from P. vitticeps and other Pogona by its relatively short tail and limbs, fewer lamellae under the fourth toe and fewer preanal and femoral glands (Witten 1994a); the specimens we observed were entirely consistent with these criteria. In captivity the two species are known to hybridise (Rybak 1996). The size details of a small number of adult hybrid specimens (n=5) are given in Rybak (1996) however meristic characters were not provided. All SVL measurements lie outside the range of Witten (1995a) being larger (ave SVL=147mm combining male and female measurements); the TL measurements also lie outside the range obtained by pooling all data for intact tails (116-141mm vs. 146-216mm) and are also relatively larger (113 vs. 128% of SVL). The same is also true of mass measurements with 159g (130-205g) for hybrids. All specimens we examined were in excellent condition and none underweight for their size. It therefore seems unlikely that the observed two-fold difference in average mass could be attributed to captive conditioning alone, but also to their larger size.
General Activity & Behaviour: Most P. henrylawsoni were observed conspicuously perched either on rocks (n=10) or branches (n=1, perched 0.4m from ground). The remainder were basking on the bitumen road (n=2, including the road kill specimen) and one was propped almost vertically against a small (0.15m tall) heavily grazed shrub on the edge of the bitumen. No specimens were observed to use fence posts as perches. All exhibited postures consistent with them basking before being disturbed by us, typically with the dorsal surface expanded and either oriented towards the sun or adpressed against rocks. Specimens #13 and 14 had their bodies vertical, no expanded dorsum with their white chest oriented towards the sun. Air temperatures when specimens were observed ranged from 29.0°C to 37.4°C while the relative humidity ranged from 31% to 42% but tended towards the lower end (mode 31%).
In the course of being captured we observed P. henrylawsoni employ several kinds of behaviours in order to avoid detection and to avoid capture once detected:
(I) crypsis- on being approached some individuals would crouch down, lowering the head and body so that it lay flat against the substrate (rock, ground surface, soil or bitumen) while remaining completely still, carefully watching our approach. Three individuals were easily captured by hand after employing this cryptic posture. Another individual, when flushed out onto exposed soil, adopted the cryptic posture and allowed us to approach to within 0.5m. They are able to blend very effectively in with the soil substrate; this along with the cryptic posture are indicated in Figure 2.
(ii) retreat- on being approached some individuals would dismount their perches (rocks or branches) and attempt to conceal themselves. Four individuals basking on rocks simply dismounted and hid behind the basking rock, where they crouched up against the base, still clearly visible since there was no surrounding vegetation. Two individuals were observed to retreat down burrows or deep soil crevices. One of these initially attempted to conceal itself in amongst a dead shrub and on being flushed out ran some 12m across open ground into a burrow. Three lizards attempted to retreat down natural crevices located within 1m of their basking site, two lizards down a burrow one <1m away and the other 12m away. The width of natural crevices utilised was no smaller than 20mm. One individual could be seen poised vertically 0.3m below the soil surface down a crevice which was at least 0.6m deep. We noticed that lizards were capable of detecting our approach (by retreating) up to 30m away. Ehmann (1992) states that “When alarmed, it scurries into a wide soil crack or an associated burrow, usually under a rock or fallen timber.” (p.138).
(iii) threat display- when approached by us all lizards adopted behaviour (I) and (ii). However on being restrained or cornered it was not uncommon for individuals to expand their dorsal surface, gape their mouth and erect their rather small ‘beard’ in a similar manner to P. barbata. Several individuals were observed when threatened to jump small vertical distances (<10cm) in attempts to bite objects overhead.
External Parasites: On one individual (#12, Table 1) small patches of orange mite were visible on the gular region and a skin fold on the head. No other external parasites were visible.
DISCUSSION
The fact that we saw no P. henrylawsoni perched on fence posts agrees with Witten (1994a) who states “The two specimens I collected were on a dirt road in black soil country. Despite spending several months in the Aramac area I never saw Pogona of this [ P. henrylawsoni ] size perching on fence posts”. Witten (1994a) continues: “It is possible that P. henrylawsoni defends territory without the normal perching behaviour of other Pogona. Almost half the other specimens in museum collections were road kills, also suggesting the species is not obvious to passing herpetologists.” Our observations run counter to the latter statement as we found the species to be conspicuous when perched on roadside rocks while travelling through the Winton region by motor vehicle at 70-80km/h. The ease with which lizards are detected on roadside rocks would depend much on the surrounding vegetation cover; at other times of the year these areas are known to support stands of tussock grass which would make passing observations of P. henrylawsoni difficult. It is notable that only adult P. henrylawsoni were seen, indicating perhaps that juveniles constitute a relatively small proportion of the population or else do not utilise perching sites as adults do. While it may be argued that this was due to observer bias, in that juveniles would be more difficult to detect due to their small size, this explanation cannot account for the fact that we were readily able to spot adult Tympanoryptis tetraporophora (SVL=60mm, Wilson & Knowles 1988) in the same areas. The absence of juveniles might also indicate rapid growth with adult size being attained in less than 12 months of age. Predators, in particular feral cats, are known to prey on this species (G. Witten, pers.comm.) and might also account for the lack of juveniles.
It would be of interest to know how frequently the species occurs beyond the roadside strip where rocks tend to be less numerous. That the artificially created roadside habitat (i.e., the displaced rocks) is utilised by P. henrylawsoni is interesting in itself for it might predispose them to higher mortality by road vehicles and also may indicate a preference for similar areas away from roads.
It is evident from this work that there exist many gaps in the basic ecology of P. henrylawsoni within its natural range. There currently appears to be no information on the species natural diet, predators, growth (although see Witten (1994b) for information on relative growth in captive specimens), population structure and little information on the timing of reproductive events. It is hoped that this work will stimulate enquires into these various aspects.
ACKNOWLEDGMENTS
We with to thank Dr. Geoff Witten for his helpful discussions, improvements to the manuscript and for providing us with several references. We also thank the referees for alerting us to the earlier usage of the name A. rankini and making available private correspondence on the subject.
Table 2 Data on seven of the Pogona henrylawsoni
No. SVL mm TL mm HL mm HW mm MASS gr SEX
1 118 129 30 28 62 m
2 116 133 31 29 70 f
3 120 128 31 28 70 f
9 117 137 33 29 78 f
12 117 139 31 29 80 f
13 138 107* 33 30 70 f
14 123 94** 32 28 78 m
AVE 121.3 133.2 31.6 28.7 72.6
* ESTIMATED 20-30mm missing
** ESTIMATED 30-40mm missing
Note that the TL measurements of #13,14 are excluded from the calculation of the average TL value.
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