Green Tree Monitors as Pets

The desirability and status associated with the green tree monitor derives from its extraordinary vivid colouration, some of the most stunning seen in the monitor family. Adults are typically a striking tropical green colour, with olive-coloured eyes and lateral bands of darker brown or black pigment extending from the back of the head down the body and along the tail, although genetic variations between individuals means that some animals may exhibit a more yellowy lime colour or even shades of blue and turquoise. As with all of its relatives in the tree monitor group (Varanus prasinus complex, which also includes V. reisingeri and V. macraei) the green tree monitor is a medium-sized monitor of a slender yet powerful build, ideally adapted for its arboreal lifestyle. Adults average 34 inches in length when mature, with more than half of this comprising an especially long prehensile tail which the monitor uses to grasp branches, in addition to long toes furnished with special gripping scales and sharp hooked claws that make it an accomplished climber and allow it to move with impressive speed and confidence around its canopy habitat. Green tree monitors originate from the tropical climate of Papua New Guinea and the Torres Straight Isles, where they may be found in a variety of habitats including indigenous rainforests, freshwater and mangrove swamp forests and wetland areas.

Behaviourally, these are a very active and intelligent monitor with a skittish temperament that do not tolerate handling by humans – wild-caught adults in particular seldom adapt well to captivity and are prone to stress-related illnesses, although captive bred youngsters may become semi-tame over time and may eventually even approach their keepers for hand-feeding. Should it become necessary to catch and restrain a monitor for removal during enclosure maintenance or for veterinary treatment, a large sturdy net such as those sold for koi carp should be used to capture the animal as quickly as possible before being carefully restrained with one hand behind the head and the other supporting the body – thick gloves are a sensible precaution as an upset green tree monitor can give a surprisingly powerful bite and will often be reluctant to release its grip once its’ gotten hold of its captor, while its long climbing talons will inflict deep scratches on bare skin. It must be emphasised that these very delicate monitors should be left untouched unless absolutely necessary – foolhardy attempts by inexperienced keepers to restrain a green tree monitor for the purposes of ‘taming’ will most likely result in painful bites to the handler and an extremely stressed monitor that may well refuse to feed.

Housing

Providing appropriate accommodation and a carefully controlled climate is fundamental in minimising stress and maintaining these specialist monitors in good health. They are an extremely active and inquisitive species and so require a generous sized arboreal enclosure, with dimensions of 6 x 4 x 2 ft (Height x Length x Depth) being an absolute minimum for a single adult, and 6 x 6 x 3 ft as a recommended minimum for a pair. The enclosure should be lined on the walls and back with cork bark panels to allow the monitors to climb and make use of all the available space, and generously furnished with branches, vines, platforms and shelves for climbing, basking and resting. The addition of sturdy live plants is valuable in helping to maintain the 80% relative humidity level required as well as providing cover and hiding areas while course grade orchid bark, coco fibre soil or leaf litter type substrates are good choices for retaining moisture, although care must be taken to check the enclosure floor regularly to remove any areas of waste or mould which may grow quickly in the warm, humid environment. An assortment of arboreal hides in the form of hollow logs or wooden ‘houses’ fixed securely onto raised platforms in secluded corners of the vivarium will often be readily accepted as sleeping areas. The addition of a small waterfall leading to a shallow pool built into the base of the enclosure is not only attractive but is also useful in promoting high relative humidity, as well as providing an additional point of interest for the occupant to investigate and may encourage them to drink. It is worth noting that many monitors will not drink from still water and instead will only lick droplets of mist from the leaves of plants, which in conjunction with the need for humidity necessitates at least twice daily sprayings of the enclosure either from a hand-held pressurised bottle or by means of an integrated misting system built into the vivarium itself. This is absolutely essential as green tree monitors dehydrate rapidly and can become critically destabilised within a matter of hours if the relative humidity is allowed to fall below 70%.

Heating and UV

Green tree monitors require relatively high environmental temperatures and should be provided with a daytime hot spot temperature of 125°F (51.6°C) directed onto a suitable basking site such as a favoured branch or shelf, and creating a thermal gradient throughout the rest of the enclosure down to a cooler area of 80°F (27°C). Digital thermometers should be used in conjunction with suitable thermostats throughout the vivarium to ensure temperatures are kept constant and prevent accidental overheating in the warm summer months. As with all reptiles, heat sources such as ceramic heaters and spot bulbs should be positioned high enough that the vivarium occupant should not be able to reach them even by jumping, however green tree monitors are particularly agile and so where possible heat elements should ideally be mounted on top of and separate to the main vivarium compartment on a sheet of heat resistant mesh above the main basking areas. The traditional heat guards used to protect basking bulbs are not ideal for use in green tree monitor vivaria, as some individuals develop a habit of jumping at and clinging to them, resulting in thermal burns to their claws and underside.

Green tree monitors also require very high levels of UVA and UVB lighting with a photoperiod of 12 hours per day – the recently developed combined UV and heat emitting mercury vapour bulbs are particularly useful for this species when positioned at least 15 inches above a basking site, although keepers should be aware that the heat output from these types of bulb cannot be controlled using traditional thermostats and so they should only be used in very large terrariums where the occupant has plenty of room to move away from the bulb in order to thermoregulate properly and avoid overheating.

Nutrition

Green tree monitors are primarily insectivores and will readily accept a range of gut-loaded livefoods including locusts, large crickets, mealworms, butterworms and cockroaches, which together should comprise around 80% of the diet. The remaining 20% should consist of protein-rich meats such as whole feeder mice and rat pups, or small portions of lean beef or rabbit mince, offered no more than twice per week. Occasionally day old chicks or quail (cut up into portions with the beak and legs removed) and whole eggs may be offered for variety, as can farm-raised snails and earthworms, although these seem to be a more acquired taste and some individuals will refuse to take them at first. Juvenilles and gravid females should be supplemented twice per week with a good quality calcium and multivitamin powder supplement, which is dusted onto feeder insects prior to release into the enclosure, while non-breeding adults only require additional dietary supplements once every 7 days. It is particularly important not to over-supplement this species, which appears to be particularly sensitive to vitamin A hypervitaminosis toxicity. Because green tree monitors are active hunters with a relatively quick metabolism compared to other varanids, it is important that they be fed little and often as this replicates the feeding pattern they would experience in the wild, so one or two small meals of insects or a single small portion of meat each day is recommended to prevent adults becoming overweight and to stimulate their natural hunting and foraging behaviours.

Breeding

The eventual goal of most keepers of this extraordinary tree monitor is to induce breeding and produce healthy captive-bred youngsters - a feat seldom achieved due to the sensitive nature of the species itself as well as limited information regarding their natural reproductive cycles and behaviours, which can make it difficult to properly prepare captive pairs for breeding.

The most successful attempts at captive reproduction in this species have occurred using sexually mature adults of at least three years of age following a period of slightly cooled temperatures and increased misting and humidity within the enclosure, designed to replicate the climatic changes that occur during the yearly tropical monsoon seasons in Papua New Guinea where V.prasinus originates. Over the winter months, the ambient temperatures and photoperiod are gently reduced to give a basking spot of around 105-110°F (40.5-43.3°C) for 9 hours a day over a period of approximately 8 weeks, during which time the frequency and duration of enclosure misting is increased to once every 3 hours for 2-3 minutes (it is important to monitor drainage at this time to prevent the substrate becoming completely sodden). As this simulated monsoon season draws to a close and the enclosure temperatures are steadily raised, a gradual increase in the amount of food offered triggers the females’ reproductive physiology in preparation for breeding. Mating usually occurs with the female hanging onto either a branch or the walls of the vivarium, while the male wraps his tail underneath hers in order to align their cloacal openings to achieve copulation, and may occur several times in a single day. Reproductively cycling and gravid females can be prone to secondary nutritional hyperparathyroidism, a form of metabolic bone disease, due to calcium being reabsorbed from the skeleton during egg formation so as soon as mating is witnessed the keeper should begin a programme of twice-weekly calcium supplementation in order to provide the female with the additional calcium she requires.

Green tree monitors can be choosy about their choice of laying site, so it may well be worth providing a selection of potential nest boxes containing different laying mediums in order to allow the female to select the one she most prefers. A large wooden nesting chamber with a removable lid and entrance hole around 10 inches in diameter positioned securely on a raised platform often works, although the use of a heavy-duty plastic black dustbin filled halfway with damp sphagnum moss with an entrance hole cut into the side using a soldering iron to ensure the edges are smooth has also been reported as highly successful in encouraging egg laying. The temperature inside the laying chamber should be maintained at 85°F (29.4°C) – the female will often reject the chamber if the substrate temperature is too low. Other laying substrates worth trying include eco-earth (coconut fibre mulch) and potting soil.

Approximately 25-45 days after mating, the female will lay between 2 and 5 eggs which she may or may not choose to bury in the laying medium. Some females will then abandon the nest box altogether and show no further interest in it, while others will be reluctant to leave their eggs and will guard the chambers’ entrance for several days. Once laying has taken place, the eggs should be carefully removed and incubated artificially using a 1:1 mixture of perlite and water – vermiculite tends not to be a good choice for tree monitor eggs, which are particularly sensitive to water logging which can cause the death of developing embryos through oxygen starvation. Provided the environmental conditions are correct, eggs incubated at 85°F (29.4°C) will typically hatch between 172 and 202 days after laying. In the hours approaching hatching, the eggs may appear to deflate and dimple slightly, before the youngsters make a cut in the egg membrane and finally emerge as brightly coloured miniatures of the adults. Hatchlings should be housed individually in smaller scale replicas of the adult habitat (large Exo-Terra or Zoo-Med glass terrariums with cork panel walls and adapted lids to retain humidity often work very well) with plenty of branches and plants for climbing and hiding. It is important that great care should be taken to ensure the ambient relative humidity is kept up and the average basking temperature should be maintained around 10°F (°C) lower than for adults in the first few weeks to prevent their tiny bodies from dehydrating. Provided they are not disturbed, babies tend to feed well and should be maintained on a well supplemented and varied diet of small insects, finely ground mince and pinky mice.