‘DINOSAUR! screamed my grandmother hysterically. “There’s a dinosaur in the backyard!”
As an eight year old, I fully expected to see a Tyrannosaurus rex strolling past, so I sprinted to the back door. There, walking slowly along with the confidence and self-assurance that is so typical of its kind, long forked tongue flicking in and out intermittently, was one of the largest lizards I had ever seen; a Lace Monitor. This was my earliest memory of these prehistoric-looking and truly magnificent lizards.
The Lace Monitor (Varanus varius) is one of Australia’s largest species of monitor, being second only in size to the mighty Perentie (Varanus giganteus). Lace Monitors frequent a range of habitats along the East Coast of Australia and are common fixtures in many camp grounds and picnic areas where they brazenly raid tents, picnic baskets and garbage bins for an easy meal. Their natural diet consists of a range of invertebrates, other reptiles, birds, frogs and carrion. Lace Monitors have razor-sharp teeth laden with a myriad of bacteria, claws designed for scaling the tallest eucalyptus trees and long powerful whip-like tails that can certainly inflict serious injury if these incredible animals are not treated with respect and caution.
I was recently asked by fellow Animal Science student Anna Tadros, who is currently undertaking her honors research into Lace Monitors at the University of Western Sydney (UWS), if I would like to assist her on a field trip acting as a ‘monitor wrangler’ to help collect data about these fascinating creatures. Who could say no to spending a week in the Australian bush surrounded by amazing wildlife, working with other passionate herpetologists catching reptiles, contributing to our scientific knowledge of a species?
Our research team headed out into a remote part of the Blue Mountains World Heritage Area surrounding the Wollondilly River which flows into Warragamba Dam and provides much of Sydney’s water supply. Being part of the catchment means most of the National Park is off-limits to the public and very few people, other than a small number of long-term residents and researchers, have access to the area.
Due to the minimal presence of humans, the abundance of native wildlife in the National Park was astonishing. During our week-long research trip we saw three species of macropod, wombats, echidnas, platypus, flying foxes, emus and many other species of birds. Surprisingly we did not see the reptile diversity I anticipated, however Red Bellied Black Snakes, Broad Headed Snakes, Green Tree Snakes and Eastern Browns are commonly found in the area. Many Short-Necked Turtles (Emydura macquarii dharuk) inhabited the river systems which were also brimming with Freshwater Yabbies and fish. Perhaps most notable, was the large population of Dingo’s which can be found throughout the Blue Mountains World Heritage Area. Although very elusive during the day, each night we would sit around a camp fire and howl to at least three packs of Dingo’s that would become extremely vocal and return our calls as they tried to identify this weird new pack that had moved into the area. This was one of the highlights of the trip for me as there is nothing quite like hearing the eerie sound of a Dingo howling through the night. Most Sydneysiders are completely unaware of the large population of Dingo’s living on the outskirts of the city. Unfortunately they are sometimes persecuted by farmers and are also at risk of interbreeding with feral domestic dogs. Fortunately, for the most part the area remains an untouched wildlife paradise.
The aim of Anna’s study was to investigate a method of sex-determination for Lace Monitors in the field, as well as looking at the home-range size of both juvenile and adult male and female wild Lace Monitors. An ultrasound machine powered by our vehicles was used to gather images of the ventral/tail regions and lower abdominal areas of specimens. Detailed morphometric data was collected including head width, head length, snout to vent length, tail length and body weight. Small GPS tracking devices were attached to several specimens using a denim pouch and strong adhesive glue. These devices were also fitted with a thermometer which was set to take regular temperature readings providing data about temperature ranges the Lace Monitors were most active in. The GPS trackers collected continuous data on the movement of the Lace Monitors until the animals shed their skin, when the trackers would simply fall off and leave us with the arduous task of finding them amongst hundreds of hectares of bush land.
The most exciting part of the trip was trying to catch as many Lace Monitors as possible in a week-long period. A number of coyote and fox traps were imported from America by the university and when baited with an extremely tantalizingly rotten rabbit carcass, these proved to be irresistible to the Lace Monitors and the most effective traps. These traps consisted of a large metal cage with a steel trip-plate on the bottom which would automatically close the door behind any unsuspecting monitor that entered the cage in search of a meal. Seven traps were set in various locations around the park and were checked many times throughout the day. We found that the monitors were most active after about 4:00pm in the afternoon, when it was still very hot but there was more shade around. It was interesting to note the different behaviors exhibited by these truly wild Lace Monitors in comparison to the habituated, fearless monitors which are so commonly seen wandering around human settlements. These wild monitors could not be easily approached and would dart straight up a tree at the first sight of a human.
Whilst we caught many animals using the traps, we also had to make the most of every other opportunity that presented itself to catch a monitor. We would frequently come across monitors running off the dirt tracks we were driving on and found using a ‘pincer’ maneuver an effective way of catching specimens by hand. This required one person to walk directly towards the monitor, who would react instinctively by climbing the nearest tree. Simultaneously, a second person would walk behind the tree the monitor was climbing and with the animal distracted by the person in front, the second person would grab them by the base of the tail and restrain their head on the ground, taking them by surprise. I can honestly say there is nothing like the adrenaline rush you receive in those few seconds between grabbing the monitor’s tail and restraining its head. Each animal reacted differently, with some going limp and giving up the minute they were restrained and others resisting strenuously. Thick, leather gloves were used and luckily we were able to keep all fingers and limbs intact, suffering only a few scratches from rogue claws.
One particularly memorable opportunistic catch occurred during our lunch break one afternoon when we decided to have a swim in the river. Whilst we were floating around enjoying the cool water, a large Lace Monitor decided to wander down to the water’s edge for a drink. We managed to ambush him from the river and I have to say he certainly was not expecting three large humans to come running at him from the water. We managed to catch him safely and collect useful data before releasing him shortly after. Another interesting and unexpected catch took place on one of our morning ‘trap patrols’ when we were surprised to discover a large female wombat who either had a taste for rotting rabbit flesh or had decided to let her curiosity get the better of her and enter one of the traps. The gorgeous girl had a large joey in her pouch and once the door of the trap was opened she darted out with an extra pair of legs dangling between her own.
Towards the end of the trip we were fortunate to discover a Lace Monitor ‘hot spot’. Whilst removing a monitor from one of our traps, no less than five other monitors were seen walking around the area within only a few hundred meters. The area was made up of a small grassy gully, surrounded on three sides by hills. On closer investigation we found numerous Kangaroo carcasses strewn throughout the gully. It became apparent that this was a Dingo ‘killing field’, an area where Kangaroos commonly come to feed, providing the Dingo’s with the perfect topography for ambush. As a result, the Lace Monitors were drawn to this area to clean up the carcasses left by the Dingo’s. A large hollow tree also stood nearby and we could hear baby birds chirping inside. We stood and observed a large Lace Monitor climb the tree, enter the hollow and shortly after all bird chirping ceased.
Although the research conducted during our trip is yet to be published, it became clear that using ultrasound as a method of sex determination for Lace Monitors in the field was not an accurate or reliable procedure. The skin on larger animals was too thick for the ultrasound to penetrate and provide clear images and it was also difficult to carry the bulky machine into remote areas and maintain power from a vehicle. However, we were able to use the ultrasound to see developing eggs inside at least one large gravid female which was exciting. Hemipenes were visible both externally and with the ultrasound on large males, however juveniles were extremely hard to differentiate between. Experienced reptile veterinarian Dr Rob Johnson proposed a method to be tested in future research using blood samples from animals and matching blood calcium levels to previously tested known levels from both male and female captive individuals. More morphometric data is also needed to provide information pertaining to head sizes and snout to vent lengths of males and females at different ages. It will be interesting to see the trends displayed in the GPS data when it is collected in the coming months.
Overall, 15 individual monitors were trapped, essential data was collected, multiple GPS trackers were deployed, in addition to the invaluable experience of observing these amazing creatures in their natural habitat. The largest individual monitor we caught was a male measuring 1.95 metres long (head to tail) and weighing just over 9kg. I look forward to working with these fascinating reptiles again in the near future. After all, it is as close as I will ever get to seeing a real dinosaur.
This article is also published in the January 2014 Issue of Scales and Tails MagazineAdd a comment