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The ecology and behaviour of Varanus mertensi (Reptilia: Varanidae)

By Phillip James Mayes

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This study examines numerous aspects of the ecology and behaviour of Merten's Water Monitor, Varanus mertensi (Reptilia: Varanidae) including; daily behaviour, diet, foraging behaviour, reproductive seasonality and daily and long-term movements. Findings from over two years of field study of V. mertensi found in waterbodies of both the Ord River Irrigation Scheme and surrounding East Kimberley/Victoria River Downs bioregion of Western Australia are presented. This study simultaneously broadens our understanding of the family Varanidae and provides insight into the life of a semi-aquatic faunal species found in waterbodies of the Ord River Irrigation Scheme.

Like other semi-aquatic varanids the daily behaviour of V. mertensi incorporates aquatic activity and like other Australian varanids it also varies seasonally. Daily core body temperatures are lower during the dry season when water temperature is low compared to the wet season when water temperature is higher. Seasonal differences in water temperature are also reflected in the daily behaviour of V. mertensi that spend more time basking during the dry season. In support of these field observations, laboratory trials showed V. mertensi rapidly cool in cold water.

Varanus mertensi is an active wide-ranging opportunistic predator of aquatic and riparian areas with a catholic diet including many relatively small prey items. It moves and searches for prey based on olfactory and visual cues in a similar way to other active foraging varanids. It is equally capable of locating and capturing prey in the terrestrial and aquatic environments and can draw on previous prey capture experience to maximise its foraging efficiency.

Females, like some other tropical Australian varanids lay their eggs during the early dry season. Dry season egg deposition combined with an incubation time of 9-10 months culminates in hatchlings emerging during the following wet season. Female V. mertensi, like most varanids, display a synchronous breeding tactic undergoing vitellogenesis just prior to the wet season mating period. However, males are asynchronous undergoing pre-emptive spermatogenesis during the late dry season prior to the mating period.

Adults move between multiple core activity areas within their large long-term activity areas and often do so on a seasonal basis. Daily and long-term activity areas closely resemble the shape of waterbodies in which individuals are found. Some V. mertensi, like other Australian varanids, burrow and remain inactive during the late dry season.

This study shows that numerous aspects of the ecology and behaviour of V. mertensi are similar to those of other similar-sized varanids just focused around aquatic areas. Varanus mertensi occupy a similar ecological niche to other semi-aquatic varanids, that of a wide ranging, active foraging, opportunistic predator of aquatic and riparian areas within their northern Australia distribution.


Megan Kendall

Purdue University

Date 2006
Pages 266
Degree Doctor of Philosophy
Language English
Notes This thesis was found at Edith Cowan University Research Online digital repository:
University Edith Cowan University
Cite this work

Researchers should cite this work as follows:

  1. Animal welfare
  2. Body temperature
  3. Foraging
  4. Health
  5. Physical environment
  6. Reptiles