Table Of ContentDIET OF VARAN US CAUDOLINEATUS
(REPTILI A: V ARANIDAE)
By GRAHAM G. THOMPSON
Edith Cowan University, Joondalup, 6027, Western Australia, and
Zoology Department, University of Western Australia, Nedlands,
6009, Western Australia
and DENNIS KING
cl- Western Australian Museum, Francis St, Perth, 6000, Western Australia
ABSTRACT
The diet of museum specimens of Varanus caudolineatus is significantly
different from those caught on Atley Station in Western Australia. The
museum specimens had a much broader range of prey types, (predominantly
spiders, grasshoppers and lizards) than those found on Atley Station that had a
very high predominance of scorpions and a lower, but significant number of
terrestrial spiders in their stomachs and intestines. These data suggest that V.
caudolineatus at the Atley site essentially forage primarily on the ground
rather than in trees as might be expected for an arboreal lizard.
INTRODUCTION (Shine 1986, Thompson in press).
Significant ecological information is
Varanids are generally reported as
often inferred from dietary data.
being carnivorous and oppor¬
tunistic feeders, eating predomin¬ Varanus caudolineatus is an arboreal
pygmy goanna that usually takes
antly invertebrates. However, a few
refuge under loose bark or in the
species specialise on prey types that
hollows of mulga trees; it is not
reflect their habitat (Losos and
usually found in spinifex or sand
Greene 1988). Diets of many species
plain habitats (Pianka 1969). Its diet
of varanids have been determined
is quite varied and includes mainly
from museum specimens (Pianka
grasshoppers, roaches and geckos.
1968, 1969, 1970 a, b, 1971, Greene
1986, Losos and Greene 1988, James This study reports the stomach
et al 1992) or from freshly caught contents of 88 Western Australian
specimens from a diverse range of Museum (WAM) specimens of V.
locations (King and Green 1979, caudolineatus and contrasts this data
Pianka 1968, 1969, 1970a 1971, 1986). with diet of 33 specimens caught in
There are few reports of the diet of December 1991 in close proximity
varanids based on stomach contents on Atley Station, W.A. (119°07E,
collected from a single location 28°25’S), 4 caught in July 1991 North
199
of Ajana, W.A. (114°45'E, 27°35'S) and fences installed on the Atley site.
the 78 other specimens (largely from
The analysis of the difference
the W.A. and S.A. Museum) pre¬
between the stomach contents of
viously examined by Pianka (1969).
museum specimens and those from
the Atley site was done using the
SPSS/PC discriminant analysis
METHODS AND MATERIALS
program.
A ventral incision was made in
museum specimens (WAM) and the
gut contents removed and identi¬ RESULTS
fied. Stomach contents or scats were
The stomachs of 46 of 88 museum
collected from 24 individual V.
specimens examined were empty.
caudolineatus caught in tree hollows
The contents of the remaining 42
and pit traps on Atley Station and
stomachs contained predominantly
four V. caudolineatus caught in tree
spiders, grasshoppers and lizards
hollows in the area north of Ajana.
(Table 1). Seven of the lizards were
Nine of the monitors were sub¬
identified as geckos, Gehyra sp., and
sequently recaptured at least five
one stomach contained at least two
days later on Atley Station and their
Gehyra sp. tails. Most stomachs
stomach contents or scats were
contained only one item but four
again collected. Stomach contents
contained two or more identifiable
were flushed with tepid water,
items.
using a technique similar to that
reported by Legler and Sullivan Three stomachs of the 4 V.
(1979). Scats were collected from the caudolineatus from the site north of
calico bags used to temporarily hold Ajana contained prey items; these
V. caudolineatus on the Atley and were a spider, a beetle and a cricket
Ajana sites. The stomach contents (Table 1).
and scats were stored in a dilute V. caudolineatus from the Atley site
solution of formalin (approxi¬ fed predominantly on scorpions,
mately 10%) for later identification. followed by a lesser number of large
Neither stomach contents nor scats spiders, that were often found in
were collected from seven of the 33 holes in the ground during the day,
lizards examined from the Atley and lizards (Table 1). Two of the
site. Three of the four lizards from lizards were skinks, one was a
Ajana provided prey items from juvenile Menetia greyii the other was
their stomach. the dismembered parts of a small
The Atley Station site contains red Ctenotus schomburgkii. In addition,
loamy soils which supports a three V. caudolineatus from the
vegetation consisting mainly of Atley site and one from the site
spinifex (Triodia sp.), grasses, mulga north of Ajana had red gravel in
(Acacia sp.) and gum (Eucalyptus sp.) their stomachs. This was probably
trees. A representative sample of the ingested while they were capturing
potential small vertebrate and prey on the ground.
invertebrate prey items were col¬ There is a significant difference (chi-
lected from 60 pit traps (20 litre square 74.63, df 6, p<0.0001) in the
plastic containers) with 10m drift gut contents of the museum
200
Table 1. The number of stomachs (and scats*) with the incidence of prey items in V.
caudolineatus
Museum Pianka Atley Ajana
specimens 1969 site* site
No specimens examined 88 78 33 4
No stomachs empty 46 44 7 1
PREY TYPE
Centipedes 1 2 1
Scorpions 17
Spiders 10 6 7 1
Grasshoppers 8 10 2
Roaches 3 11
Moths 1 1
Larva 4 4 0
Beetles 1 1 1
Unidentified invertebrate 8 6 0
Egg sac 1
Bee 1
Cricket 1
Lizards — egg sac 1
- other parts 9 10 3
Twigs 2 1
Red gravel 3 1
* the contents of lizard scats are included in the data from the Atley site.
specimens we examined and those specimens we examined and those
caught on the Atley Station. 91.2% examined by Pianka (1969), with the
of the gut contents were classified exception that Pianka's sample
correctly with the group centroids contained a relatively higher
being 1.95 for the Atley site and - number of roaches. This similarity
1.13 for the museum specimens. would have been expected.
Potential prey items captured in the There is however a significant
60 pit traps located on the Atley site difference between the diets of V.
were placed into three groups, caudolmeatus found on the Atley
depending on their relative site, and those examined by us in
abundance in the traps (Table 2). In the Western Australian Museum
addition, Gehyra variegata and collection. The very high pre¬
Egernia depressa were found in dominance of scorpions and lower,
relatively low number in trees in but significant number of ter¬
which V. caudolineatus were found. restrial spiders in the stomachs and
intestines of V. caudolineatus from
the Atley site contrasts with the
DISCUSSION
much broader range of prey types in
There is a similarity between the the museum specimens we
stomach contents of the museum examined and in Pianka’s (1969)
201
Table 2. Relative abundance of potential prey items found in pit traps on the Atley
site.
Pit trap catch frequency
Often Seldom Rarely
Item caught caught caught
INSECTA
Thysanura (silverfish) *
Blattodea (roaches) *
Isoptera (termites)
Mantodea (preying mantids)
Orthoptera (grasshoppers) *
Phasmatodea (stick insects)
Coleoptera (beetles) *
Hymenoptera (ants) *
ARACHNIDA
Scorpionida (scorpions) *
Araneae (spiders) *
CHILOPODA
Scolopendrida (centipedes) *
REPTILIA
Scincidae (skinks) *
Gekkonidae (geckos) *
Varanidae (goanna) *
samples. In this particular cir¬ for them to become prey for V.
cumstance the stomach contents of caudolineatus. The small skinks
specimens coming from a variety of caught in the pit-traps were
locations [museum and Pianka predominantly Ctenotus schomburkii
(1969)] do not necessarily provide a and Ctenotus leonhardii, while
good indication of the diet of the the predominant gecko was
same species at a particular site. This
Rhynchoedura ornata. C. schomburkii
is similar to the situation for V. and R. ornata appear to be within
mertensi (Shine 1986). the suitable prey size range for V.
The different diet of the small caudolineatus to ingest but may be
monitors at the Atley site probably too difficult to locate and capture.
reflects the food items available and C. leonhardii is a larger skink and
able to be captured and ingested.
may be too fast and too large for V.
Centipedes were abundant there,
caudolineatus to capture. Gehyra
but the adults may be too large or
variegata, which was relatively
too difficult to subdue. Many of the
abundant in the stomachs of
beetles present there might also
museum specimens, but was not
have been too large and their exo¬
found in the stomachs of the Atley
skeletons too difficult to penetrate
site monitors, was caught only once
202
in the pit-traps, but were specific conclusions about the diets
occasionally found under the bark of varanids at a particular location
of trees. from museum specimens or from
those caught in other locations. It
All identifiable species of scorpions
would be interesting to know
and spiders found in the stomachs
however, if there was a relationship
and scats of these small monitors are
between the density of V.
ground dwelling invertebrates. In
addition, both M. greyii and C. caudolineatus and the high availa¬
bility of scorpions at the Atley site
schomburgkii are both ground
or whether this small monitor
dwelling skinks that live around
would feed on other invertebrates
the base of spinifex clumps or in
in the absence of scorpions.
holes in the ground. This supports
other behavioural data (Thompson, Contrary to Pianka’s (1969) sug¬
unpublished) that indicate that V. gestion that V. caudolineatus are
caudolineatus retreat to trees when not found in spinifex habitats, most
threatened, to sleep or to observe of the Atley sites from which V.
their surrounds, but essentially caudolineatus were collected had
forage on the ground. patches of spinifex ground cover
No V. caudolineatus were captured at and a sparse cover of mulga trees.
night in the pit-trapping program
on the Atley site, although the
ACKNOWLEDGEMENTS
ambient temperature at night was
often in the mid-to-high 30°C’s. The field work component of this
Scorpions, and many of the spider research was made possible by the
species that were preyed-upon, were financial assistance of Edith Cowan
only found out of their burrows University and the University of
after dark. On two occasions in soft Western Australia. The assistance of
red loamy soils clear tracks of V. P. Hately, W. Thompson and S.
caudolineatus were found leading to Thompson in digging in pit-traps,
the entrance of scorpion holes, catching V. caudolineatus and
suggesting that these lizards enter checking pit-traps was very much
burrows in search of prey. The red appreciated. The comments of P. C.
gravel in the stomachs of monitors Withers significantly improved the
may be ingested when they are manuscript. K. Aplin and L. Smith
eating scorpions or spiders captured provided access to the collections of
in burrows. the Western Australian Museum.
This study provides further support The approval by R. and J.
for the point made by Shine (1986) Broadhurst to have access to Atley
and Thompson (in press) that the Station was appreciated. All lizards
diets of varanids vary significantly were caught under licence issued by
with locality and time of the year. the Department of Conservation
Much of the dietary data and the and Land Management to G.
derived ecological information for Thompson. Animal experimenta¬
varanids comes from museum tion on live specimens was done
specimens (Losos 1988, Greene 1986, with the approval of the Animal
James et ai 1992). It would therefore Welfare Committee of the Uni¬
appear inappropriate to draw versity of Western Australia.
203
REFERENCES PIANKA, E.R. 1969. Notes on the
Biology of Varanus caudolineatus and
GREENE, H.W., 1986. Diet and
Varanus gilleni, West. Aust. Nat., 11:
Arboreality in the Emerald Monitor,
76-82.
Varanus prasinus, with Comments
on the Study Adaptation. Fieldiana PIANKA, E.R. 1970a. Notes on the
Series No 31: i—12. biology of Varanus gouldii flavirufus,
KING, D. and GREEN, B. 1979. Notes West. Aust. Nat., 11:141-144.
on Diet and Reproduction of the PIANKA, E.R. 1970b. Notes on
Sand Goanna, Varanus gouldii Varanus brevicauda, West. Aust. Nat
rosenbergi, Copeia, 1979: 64-70. 11: 113-116.
JAMES, C.D., LOSOS, J.B. and KING,
PIANKA, E.R. 1971. Notes on the
D.R. 1992. Reproductive biology and
biology of Varanus tristis, West. Aust.
diets of goannas (Reptilia:
Nat., 11:180-183.
Varanidae) from Australia, ].
Herpetology, 26: 128-136. PIANKA, E.R. 1986. Ecology and
LEGLER, J.M. and SULLIVAN, L.J. Natural History of Desert Lizards,
Princeton Uni. Press, Princeton, N.J.
1979. The Application of Stomach-
Flushing to Lizards and Anurans, SHINE, R. 1986. Food habits, habitat
Herpetologica, 35: 107-110. and reproductive biology of four
LOSOS, J.B. and GREENE, H.W. 1988. sympatric species of varanid lizards
Ecological and evolutionary impli¬ in tropical Australia, Herpetologica,
cations of diet in monitor lizards, 42: 346-360.
Brit.]. Linnean Soc., 35: 379-407. THOMPSON, G.G. (in press). Notes
PIANKA, E.R. 1968. Notes on the on the diet of Varanus gouldii in a
Biology of Varanus eremius, West. semi urban environment, West.
Aust. Nat., 11: 39-44. Aust. Nat..
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