Diet and reproductive status of a road-kill Spencer’s Monitor Varanus spenceri (Lucas and Frost, 1903).
By Robert A. Valentic and Grant Turner.
Spencer’s monitor, Varanus spenceri, is a moderately large robust monitor lizard endemic to the black-soil plains of western QLD and central-eastern NT (Dale 1973, Wilson & Knowles 1988, Ehmann 1992). Relatively little has been published on the natural history of this species since its original description by Lucas & Frost in 1903 (e.g., Dale 1973, Green & King 1993). Pengilley (1981) provided details on the species’ diet and reproduction (timing and clutch size) based on the dissection of specimens from the Barkly Tableland region, NT. Ehmann (1992) provided notes on the species habits and diet. Other than these works the remainder of the published material is mostly anecdotal or derives from captive lizards and includes the successful captive breeding of the species (Peters 1968, 1969ab, 1971, 1986 see also Christian 1979). In this note we provide additional details on diet and reproduction through the dissection of a single road-kill V. spenceri.
At approximately 1530hrs. (CST) on 18 October 1996 a severely injured adult V. spenceri was observed lying upturned on the Barkly Hwy (137°42’E, 20°01’S), 32km west of the NT-QLD border (and 45km west of Camooweal (138°06’E, 19°55’S), QLD. Weather was overcast with heavy cloud cover, a gentle south-easterly breeze and light rain. Air temperature was 24.0°C and relative humidity 60%. The area had evidently received rain during the last few days though there was no standing water. Habitat consisted of ‘black‘-soil grassland plain, lacking middle and upper vegetation layers. The ground layer consisted of well-spaced Mitchell grass (Astrebla spp.) tussocks separated by patches of exposed brown friable soil with numerous cavities.
On closer inspection of the lizard it was found to be still alive. It was observed to exhibit gular pumping and periodic gaping of the mouth as though trying to regorge. As both rear limbs were broken along with the pelvis, it was thus decided to euthanase the lizard. Dissection confirmed that the specimen had been hit in the pelvic region. The pelvis was broken in two as were the tibia and fibula of the right rear limb, the tibia of the left rear limb, and there was extensive internal bleeding in the pelvic region.
The lizard’s dimensions were as follows: snout-to-vent length (SVL) 435mm, tail length (TL) 445mm, head length (HL; as measured from the tip of the rostral scale to the anterior edge of the tympanum) 58.7mm and head width (HW; measured at the mid-tympanum level) 34mm.
Upon dissection the specimen was found to be a gravid female, with 13 late stage shelled eggs filling much of the abdominal cavity. (see Figure 1.) The 13 eggs, three of which had evidently burst when the lizard was hit, were removed from the oviducts (7 in left, 6 in right). All egg shells were clean, white and turgid and tended to collapse slightly under their weight when placed on a flat surface. Egg dimensions and weights are given in Table 1. Egg albumen was uniform lemon yellow in colour with no visible embryo. This is apparently the case for viable eggs at the time of deposition (G. Fyfe, pers.comm.).
Several clearly identifiable prey items were present in the gut. Two adult Ctenotus joanae (#1 SVL=76mm, TL=117mm, 26mm was regenerated and some 10mm was missing; #2 SVL=79mm, TL=138mm, 47mm regenerated). The head of specimen #1 was crushed and there were clear bite marks on the neck and mid-body region and isolated tooth punctures on the ventral surface. Specimen #2 appeared to have been consumed earlier than #1 and was partly eviscerated. Two small iridescent green beetles (each 8mm long) were amongst the viscera and were probably consumed by #2. A very recently ingested adult male Tympanocryptis tetraporophora (SVL=59mm, TL=100mm, sex confirmed by everting hemipenes) was also found lodged in the throat of the specimen and showed no externally visible bite marks or injuries. None of these prey items were chewed. In addition to these items a large roach (blattodea, approx. 30mm long, too large to have been secondarily ingested) was identified from intact abdominal segments and was observed to be common beneath ground debris on the plain where the lizard was taken.
The presence of external and internal parasites was noted. Two clusters, each of 12 ticks, occurred just below the pectoral region of the ventral surface and about 15mm past the vent on the underside of the tail. A number of small live transparent nematode worms (20-25mm in length) were located inside the oesophagus, on the T.tetraporophora and the C.joanae prey items and in the gut.
Figure 1. Dissected Spencer's Monitor Varanus spenceri showing the eggs and distended An adult Spencer's Monitor Varanus spenceri from Muttaburra, stomach. Eyrean Earless Dragon Tympanocryptis tetraporophora at top right of Queensland, Australia
A sub-adult Spencer's Monitor Varanus spenceri from Brunette Downs, An adult Black-soil ctenotus Ctenotus joanae from west of Camooweal, Queensland, Australia
Northern Territory, Australia
V.spenceri feed on a broad range of prey items, which is typical of the larger varanids (Losos & Green 1988, King & Green 1993). Pengilley (1981) records V.spenceri as feeding on isopods, orthopterans (grasshoppers), unidentified mammals (‘probably Rattus villosissimus’), and reptiles, with single records of an unidentified agamid and an elapid snake, Pseudonaja ingrami. Wilson & Knowles (1988, p.360) state that the species feeds on a variety of small vertebrates, anthropods and carrion. Ehmann (1992, p.156) states ‘Adults hunt lizards, snakes, large insects and small mammals’ and juveniles as eating ‘isopods (which abound in the soil crevices they frequent), small geckos and skinks’.
The prey items we recovered have not been previously identified in the diet of V.spenceri. Both C.joanae and T.tetraporophora are relatively small fast diurnal species, while V.spenceri is noted as not being particularly agile (Christian 1979), not surprising given its robust build. This may suggest that the lizards were detected in, and extracted from, refugia rather than being preyed on when surface active. This mode of foraging is known to occur in varanids (Green & King 1993, p.14, Valentic 1994). As the female was heavily gravid it would be expected that her movements were more restricted, lending support to the suggestion.
Green & King (1993, p.32) noted that in V.tristis and V.scalaris most gravid females carrying ‘nearly developed eggs’ had empty stomachs and suggested that this was due to the limited space and pressure created by eggs on other internal organs. It is therefore notable that even though heavily gravid the road-kill V.spenceri had recently been feeding. G.Fyfe (pers.comm.) has noted that in captivity gravid females of the species only cease feeding about one week before ovipositing.
Pengilley (1981) recorded that all specimens (>14) collected from late September to early October were gravid, or had very recently oviposited, and that the clutch size varied from 11 to 31 (n=31); this is consistent with our observation. Observations on captive specimens (Peters 1969ab, 1971, Christian 1979) broadly agree with the timing of reproduction in temperate zone species in James et al. (1992). Pengilley also gave the dimensions of five recently laid eggs: average length 47.8mm (range 47.3-49.6mm) and average width 30.6mm (range 30.0-31.0mm) which are quite close to the egg dimensions in Table 1 suggesting that the latter were close to full term. The size of the specimen we examined is within the size range of ovigerous females found by Pengilley (1981).
Table 1. Varanus spenceri egg dimensions (n=10).
LENGTH (mm) WIDTH (mm) MASS (g)
45 30 12
45 30 19
45 29 20
42 30 13
42 29 13
40 27 20
45 30 21
44 30 18
41 30 18
40 30 18
AVE. 42.9 29.5 17.2
We thank Greg Fyfe for providing us with information on his captive breeding of V.spenceri and the referees, for their helpful comments and improvements to the manuscript.
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