Herpetological articles

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Robert A. Valentic

Valentic, R.A. 1997 (a).  Monitor - Journal of the Victorian Herpetological Society inc. 8(2): 170.    

INTRODUCTION

“Most snakes can swim” (Ehmann, 1992).  The larger frog hunting elapids (e.g. the Red-bellied Black Snake Pseudechis porphyriacus) are conspicuous and efficient swimmers (Jenkins and Bartell, 1980).  The following report is based on a small terrestrial elapid species that appears in my opinion to be an unlikely candidate for a swim.

OBSERVATION
Location:  Winnecke (Sugarloaf) Reservoir,  Christmas Hills, southern Victoria  (37°41’S, 145°19’E).
Date:  14/12/1989.
Time:  22:18hrs (Eastern Standard Time,Daylight Savings in effect).
Weather Conditions:  23°C, no breeze, clear night and full moon.

Habitat:  Barren, clay-based littoral zone of an artificial water impoundment with a northerly aspect.  Lake level low, resulting in approximately 15 metres of exposed shoreline comprised of shale.  Above the high water mark a gentle slope vegetated with dry sclerophyll forest with a dense understory of Wallaby Grass Poa sp. and introduced Common Bracken Pteridium aquilinum.

Whilst fishing along the narrow point of a small bay, my attention was drawn to a disturbance on the surface of the calm water about 6 metres out from the bank.  The moonlit conditions aided visibility and the object was ascertained to be a snake as it slowly swam closer.  The snake was scooped out of the water with my landing net and its identity confirmed with the aid of a torch.  The sub-adult Cryptophis nigrescens was a male with a SVL of 195mm.

DISCUSSION
It appeared that the C. nigrescens had entered the water from the opposite bank of the bay, some ten metres from the capture site.  Judging by the slow and deliberate swimming action, the snake did not appear to have been startled and/or escaping from a predator.  The C. nigrescens possibly travelled some distance down to the shoreline from the bushland above to forage for frogs.  The exposed nature of the littoral zone, combined with a fluctuating water level, would render it as unsuitable for a long-term microhabitat.  Small snakes heat up and cool down quickly and tend to be shuttling thermoregulators - heating and cooling many times during activity (Shine, 1991).  It is possible that the C. nigrescens was utilising the water for this purpose, noting that the weather conditions were atypically warm for the region at the time of the observation and preceded high day-time temperatures (>35°C).

Potential predators include the Rainbow Trout Salmo gardneri and Brown Trout Salmo trutta; both species occur in the reservoir.  S. gardneri is known to prey upon Eulamprus quoyii (Daniels and Heatwole, 1984) and E. tympanum (Lintermans, 1992) and may likely prey on small snakes if the opportunity arose.

REFERENCES
Daniels, C. and Heatwole, H. 1984.  Predators of the Water Skink Sphenomorphus quoyii.  Herpetofauna 16(1): 6-15.
Ehmann, H. 1992.  Encyclopedia of Australian Animals - Reptiles.  Angus and Robertson, Pymble, N.S.W. 495pp.
Jenkins, R. and Bartell, R. 1980.  A field Guide to Reptiles of the Australian High Country.  Inkata Press Pty Ltd: Melbourne, Victoria.  278pp.
Lintermans, M. 1992.  Predation on Eulamprus tympanum by Rainbow Trout.  Herpetofauna 22(1): 34.
Shine, R. 1991.  Australian Snakes - A Natural History.  Reed Books Pty Ltd: Sydney, N.S.W.  223pp.