A thread to share data as well as photographs of various members of
Varanidae.
For starters...
Behavioral plasticity and activity in
Varanus salvator, the Asian water monitor
Mammal-like Feeding Behavior of Varanus salvator and its Conservational Implications*
"Lumpini Park is a fenced 58 ha public park located
in the heart of Bangkok, surrounded by a hyper-urban
environment and heavily trafficked roads
The park is open to the public during daytime hours
and is usually teeming with people engaged in jogging
and other sporting and recreational activities. Lumpini
Park includes a notable (and probably dense) population
of V. salvator. I have seen monitors of all size-classes
– from small juveniles (ca. 30 cm in total length [TL])
to very large adults of 2.5 m TL or more (estimated
from a distance). The monitors are easily spotted, either
swimming in the ponds or canals or on the shores, usually
within10 m from the water’s edge. Less frequently, they
may move away from the water – 50 m or more from
the water’s edge. Juveniles and small adults (< ca. 80
cm TL) climb trees, concrete fences and other manmade
structures. The monitors also regularly enter the
park’s underground draining system. Contrary to most
other places in Thailand, people refrain from fishing in
Lumpini Park, therefore the ponds seem to hold sizable
populations of fish, turtles and other aquatic animals. I
have observed water monitors feeding on walking catfish
(Clarias sp.), swamp eels (Fluta alba), barbs (Puntius
sp.), suckermouth catfish (Hypostomus plecostomus),
Asian box turtle (Cuora amboinensis) and food leftovers
discarded by picnickers in the park. The V. salvator of
Lumpini Park are habituated to humans and seem to
be indifferent to their presence at distances of 2-3 m or
more. Below 2-3 m, they usually flee (usually into the
water) or display various threatening postures.
At 1405 h on 6 January 2010, I spotted a V. salvator
(ca. 140 cm TL; estimated from a distance + another ca.
10 cm of missing tail tip) outside the fence surrounding
Lumpini Park, ca. 5 m from a water canal. The monitor
was engaged in eating a suckermouth catfish H.
plecostomus (ca. 45 cm TL, estimated from a distance).
At first, the monitor tore a hole in the skin and bore its
head into the body, much like a vulture eating softer
inner parts of a carcass. It then proceeded to rip the
body apart with its jaws using its forefeet for assistance,
consuming smaller chunks of meat at a time. By
1440 h, a substantial amount of the fish had been eaten;
parts which remained included the head, pectoral fins,
vertebral column, and tail.
At 1453 h, the monitor
succeeded in severing the vertebral column, separating
the hind part of the body (altogether ca. 20 cm), and
took less than 3 min to swallow it whole in an anteriorposterior
orientation. During this process, the
monitor stopped all eating activities and observed me
motionlessly for ca. 2 min. What remained of the fish at
this stage included most of the head, especially the hard
dorsal part covered with bony shields, the pectoral fins,
and about 10 cm of the anterior spinal cord that remained
attached to the head. The monitor then left the
fish, defecated, and foraged in the area for ca. 5 min,
using typical varanid foraging behaviors, eating smaller chunks of meat and other leftovers from
the fish that were scattered in the immediate vicinity.
At 1503 h, the monitor returned to the remains of the
fish carcass and continued to rip it apart. At 1505 h, it
yawned, then unsuccessfully tried to tear off parts of
the head. It then moved ca. 4 m away from the fish,
walked under the fence into the park and then returned
to the vicinity of the fish where it resumed foraging,
characterized by thorough searching accompanied by
repetitive tongue flicks, traveling back and forth into
and out of the park. At 1515 h, another two V. salvator
emerged from the nearby canal (ca. 2 m and 1 m TL). At 1525 h, it began to rain and the observation was
terminated. The net observation time for the feeding
behavior lasted 70 min and was carried out from a distance
of 3-4 m. Although the feeding monitor usually ignored
me completely, it does appear that my presence did cause
minor disturbance since it occasionally stopped eating to
observe me and the surroundings for 5-30 sec. before resuming eating; these pauses infrequently lasted
longer than a minute (1-2 min). On several occasions,
the monitor carried the fish 3-5 m away from me in an
effort to continue eating behind vegetation and a fence.
It is well known that V. komodoensis occasionally
preys on feral domestic horses and water buffaloes
(Auffenberg, 1981) that obviously cannot be swallowed
wholly. In terms of feeding and foraging behavior and
hunting tactics, V. komodoensis constitutes a category
of its own, somewhat detached from other varanids
(Auffenberg, 1981). There are no reports on such
a behavior in V. griseus, but it cannot be ruled out
(Stanner, 1983). Morphologically, there is no reason
why V. griseus (or other medium-sized varanids that
are strong enough) would not use such prey-handling
techniques. In that respect, unlike snakes whose teeth
are posteriorily curved, conical and round in transversesection,
and adapted only for holding the prey in place
and preventing it from sliding out of the mouth during
the process of swallowing, the teeth of Varanus are
bi-laterally compressed and serrated (Mertens, 1942;
Gaulke & Horn, 2004), which enables cutting and tearing
off pieces of flesh. Karunarathra et al. (2008) observed
a 2 m V. salvator swallowing a 50 cm suckermouth
catfish in the Bellanawila-Attidiya Sanctuary in Sri
Lanka; hence, it can be concluded that water monitors
are capable of either swallowing suckermouth catfish
wholly, or ripping them apart into smaller pieces with
their jaws and feet as described above. The monitor in
Bellanawila-Attidaya was 2 m long (vs. 1.4 or 1.5 m
in Lumpini Park) and the fish – 50 cm (vs. 45 cm in
Lumpini Park); therefore, predator/prey length-ratio in
Bellanawila-Attidaya was 4, vs. 3.1 or 3.3 respectively
in Lumpini Park. It can therefore be postulated that
upon attempting to eat a suckermouth catfish, or any
other type of prey for that matter, V. salvator considers
either or all of the following factors: the species of the
prey, its morphology, and the predator/prey size-ratio.
If the predator/prey size ratio is large, the monitor
will consume the prey in the easiest and quickest way
possible, by swallowing it whole. If the predator/prey
size ratio is not large, or if the prey’s morphology makes
it too difficult, hazardous or impossible to swallow, the
monitor will rip the prey apart instead.
...
Monitor lizards are the most loathed animals in
Thailand, and of the four species native to Thailand, V.
salvator is by far the most loathed. The Thai name for
this species is “Hia”, which is considered an extremely
offensive and abusive word that Thais are reluctant to
even mutter. Due to their unpopularity, Thais do not
consider monitor lizards in general, and water monitors
in particular, as worthy species for protection and
conservation. Varanus salvator can eat suckermouth
catfish of all size-classes; hence, they may now have
an opportunity to change their negative image, become
the main biological controller of suckermouth catfish,
and help save fresh-water ecosystems of Thailand.
Moreover, V. salvator routinely scavenge for food and
are capable of eating decaying carrion (Stanner unpub.
data; Traeholt, in Bennett, 1998). Water monitors can
eat large prey by ripping it apart (this study) and are
capable of eating carrion of all size-classes including
human corpses (survey in Bennett, 1998). Contrary to
the general public, Thai officials that are responsible
for the management and maintenance of fresh-water
ecosystems usually acknowledge the important role of
water monitors in maintaining sanitation in fresh-water
reservoirs and ecosystems, all of which may be useful
for promoting the conservation of this species."
*Cite:
STANNER, MIcHAEL. "Mammal-like feeding behavior of Varanus salvator and its conservational implications." Biawak 4.4 (2010): 128-131.
A remarkable Feeding Behavior and a new distribution record of Varanus salvator salvator (laurenti, 1768) in eastern sri lanka
Abstract
We describe a unique feeding behavior of Varanus s. salvator observed within lahugala national park, sri lanka. the lizard was observed lashing its tail quickly from side to side while submerged in a shallow waterhole, which displaced water and fishes from the waterhole onto the land. More than 30 fishes were expelled onto the land, of which many were subsequently consumed by the monitor. This observation highlights the significance of isolated waterholes in the dry zone to sustain wildlife populations during the dry season, and represents a new distribution record for V. s. salvator in eastern sri lanka.
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*This image is copyright of its original author
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*This image is copyright of its original author
Observations on Varanus s. salvator in North Sulawesi
Abstract
Asian Water Monitors (Varanus s. salvator) are widespread on the main island of Sulawesi,
Indonesia, but rather rare in the province of North Sulawesi because of human predation. This study
documents observations on the daily behavior of a small coastal population over a two week period.
Observations of aquatic behavior led to discussion of the possibility that this population is able to catch
live fish in a particular coastal lagoon.
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*This image is copyright of its original author
Link to study
