gondwana reptile productions by rob valentic about us

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Agamid predation by a Black-palmed Monitor Varanus glebopalma (Mitchell, 1955).

A field observation.

By Rob Valentic
INTRODUCTION
The Black-palmed Monitor Varanus glebopalma is a moderately large, streamlined monitor confined to tropical far northern Australia.  Saxicoline, the species inhabits sandstone (also quartzite rock e.g. Mt Isa district, Qld) ranges and escarpments, particularly those adjacent to watercourses within gorges (pers. obs.).  The following account is based on an adult specimen running down and subsequently consuming a sub-adult female Gilbert’s Dragon Amphibolurus gilberti.

LOCATION
Umbrawarra Gorge Nature Reserve in the ‘Top End’ of the Northern Territory.  The reserve is located 32km via unsealed road south-west of the mining township of Pine Creek (1349’, 13150’).

HABITAT:
Rugged sandstone escarpment with intersecting gorge falling away to stepped cliffs with attenuated slopes.  Vegetation cited from Kerle, 1996;  “On the undulating plateaux and plains are open forests with mixed stands of Darwin woolly butt Eucalyptus miniata and stringybark E. tetrodonta, with a shrub layer and ground layer dominated by sorghum species. Other species include fan palm Livistonia humilis and zamia palm Cycas armstrongii.  Other associations on the undulating country include northern box E. tectifica, round-leaved bloodwood E. latifolia and ironwood Erythrophleum chlorostachys with fan palms and tall grasses such as sorghum and giant spear grass Heteropogon triticeus.”

OBSERVATION
Date:  10th November 1991.  
Time:  18:30-19:00hrs (Central Standard Time).
Temperature:  34C, clear, no breeze, relative humidity 80% (approx.).
An adult Varanus glebopalma was observed actively foraging along the Umbrawarra creekbed at twilight.  The species is opportunistic in regards to activity patterns.  Individuals may be sighted diurnally active at any period (per. obs.), in addition to crepuscular and nocturnal behaviour (Shea et al., 1988).

Whilst hiking along a walking track running parallel to the creekbed, my attention was drawn by the rustling of foliage a few metres to my left.  A medium-sized agamid subsequently burst through the undergrowth and bolted across the path less than one metre in front me with an adult Varanus glebopalma hot on its heals.  Both lizards covered some thirty metres of terrain; along the sandy creekbed, across a sandstone overhang and atop a boulder strewn slope where the chase ended abruptly.  Amphibolurus gilberti are very swift runners and the distance covered took no longer than five seconds.

The goanna had seized the agamid around the mid-body and lowered its head into the sandstone in a manner that pinned the victim onto the substrate.  It then manipulated the dragon’s anterior half inside the jaws and swallowed the prey head first and struggling.  It was during the swallowing process that the species of unidentified agamid was ascertained.

DISCUSSION
A sight and subsequent run down feeding approach is employed by all the swift species of Varanids and some Elapid genera (eg.; Pseudonaja, Demansia).  Varanus glebopalma are highly adapted in regards to this technique due to their slender build and extreme agility when mobile on uneven surfaces.

REFERENCES
Ehmann, H.  1992.  Encyclopedia of Australian Animals - Reptiles.  Collins/Angus and Robertson Pty Ltd, Pymble, NSW, Australia. 495pp.
Kerle, J.A.  1996.  Bioregions of the Northern Territory. Draft report Conservation Commission of Northern Territory, Palmerston, Northern Territory.
Shea, G., Weigel, J., Hardwood, A., Floriani,, H. Hemsley, C.  1988.  Notes on the Herpetofauna of Mitchell Plateau, W.A. Herpetofauna 18(1):16.
Wilson, S.K. and Knowles, D. 1992.  Australia’s Reptiles - A Photographic Guide to the Terrestrial Reptiles of Australia.  Collins/Angus and Robertson Pty Ltd, Pymble, NSW, Australia. 447pp.