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Varanus becarri is commonly known as the Black Tree monitor or Aru Island monitor. As the name suggests, they hail from the Aru Islands located just off the west coast of New Guinea. These are small varanids, relativly speaking, that spend the majority of their lives in the treetops of the island's forests as well as mangrove swamps and vines. There is not very much known about the natural history of the Black Tree monitor and this could, in part, be due to their arboreal nature and small size.
These monitors were once thought to be a subspecies of Varanus prasinus or even a color morph of the Green Tree monitor. Currently they are recognized as a distinct species. This whole tree monitor complex encompasses a number of monitors whose taxonomy is not fully clear: e.g. Varanus prasinus, Varanus prasinus kordensis, Varanus bogerti, Varanus teriae, Varanus telenesetes, Varanus keithhornei For our purposes (captive care), we will deal with the Black Tree monitor as it is currently recignized; a full species. It is likely that captive husbandry will be very similar for the entire group anyways.
Most, if not all of these monitors seen in the pet trade are wild caught. Captive breeding is rare but has been accomplished by a few zoos and private keepers so obtaining a CB (captive bred) specimen will not be an easy task.
Physically, they are very much like the Green Tree monitor but may grow to a slightly larger size. Their anatomy reflects their arboreal nature. They are slightly built monitors that have a long neck and small head. The teeth are long and sharp as would be expected of a tree dwelling predator. The long teeth enable them to better hold on to prey in the canopy. The limbs are long and skinny and the toes are armed with needle sharp nails to grip the branches they climb on. The tail is roughly twice as long as the SVL (snout to vent length) and fully prehensile, essentially giving it a fifth limb.
The color at birth is reported to be lighter with green banded markings across the body (Bennett, 1998) but will turn a uniform black as it becomes an adult. Some may think this color is drab looking but these active varanids make wonderful display animals in a nicely planted enclosure.
Varanus becarri is from a tropical climate that experiences high daytime temps. In the wild they would likely be able to thermoregulate by basking in the sunlight that penetrates the canopy or in areas that are in full sunlight. I don't know this for sure but it is a feasable thought. In any case, you will need to provide the monitor with the proper heat and light it requires to thrive in captivity.
In captivity, Black Tree monitors have been kept successfully in setups that offer a basking temperature in the 100-110°F range. The ambient temperature can be around the 85°F mark.
Depending on the size and shape of your tank you will have to find the right combination of bulb(s) needed to offer the correct range of temperatures. "Reptile" basking lights or regular flood lights are good for providing heat in a desired area (basking site) but if you find that this bulb doesn't sufficiently heat the enclosure you may need to use additional bulbs. Ceramic heaters don't emit light and are good for this sort of ambient heat. Be sure that there is a temperature gradient in the enclosure and not a uniformly hot environment because this will put stress on the animal. They should be able to go from hot to cold (so to speak) whenever they want to. Warning: Make sure your Black Tree monitor can not come into direct contact with the heating element because it can severely injure itself. Their sense of touch is not the same as ours and the monitor may burn itself without knowing it. Use some sort of screening or make sure the heating device is far enough away that the monitor can't reach it.
If the light emitted by the basking site(s) is not bright enough for the cage you can install a flourescent fixture for added light. A regular photoperiod of 12 hours light : 12 hours dark can easily be achived with the use of a simple timer that can be purchased at any hardware store. Don't be affaid to experiment with this cycle to see if there is a better light to dark ratio for your monitor or if it makes no difference at all. I won't get into the whole issue of whether or not monitors need UV lighting, except to say that there is no definitive proof to show that they need it in captivity or to show that they suffer from receiving it. Many people have successfully kept monitors both ways. You can do some research and make your own informed decision on this one.
During the night the ambient temperature should not drop below the 75°F mark. The easiest ways to prevent this would be to either use ceramic heaters or room heaters. If you live where the temperature is always warm then you won't have to worry about this problem.
When buying or building an enclosure for Varanus becarri you should be thinking height more than length. Remember they will feel more at home in a vertically oriented cage that allows them to climb. This is not to say that you don't have to provide them with a reasonably sized surface area for when they do come down. As a minimum, an enclosure with dimensions 5 feet long X 4 feet high X 2.5 feet deep will house a pair. This is only a suggestion . Of course the more space you provide them with the better off they will be.
Black Tree monitors can be nervous animals that will want to remain hidden until they become comfortable in there surroundings so a densly planted cage will work well. You can buy fake plants, leaves and vines in the craft section of many stores for a reasonable price. You will also have to provide branches for the monitors to climb on in the enclosure. These should be securly fixed to the walls and sturdy enough to hold the weight of the monitor. Some specimens of Varanus becarri remain shy and nervous while others acclimate well and adjust to captivity. In both cases it is good practice to provide the animals with hide boxes placed in various parts of the cage. Arboreal hide boxes will be used and should be placed high in the cage with an entrance hole large enough for the monitor to comfortably enter. There are many "ready made" products on the market that can serve this purpose, for example any number of appropriatly sized nesting boxes for birds make good arboreal hide boxes. Make sure they are securly fastened in place and lined with substrate. Another good feature to consider when buying or building an arboreal hide box is accessibility. You will need a way to get in and clean it, access your monitors or if you're lucky--collect some eggs! It is conceivable that in the wild Varanus becarri would use hollow tree trunks for hiding in so with a little creativity you can probably re-produce a similar setup.
Cypress mulch makes a good substrate for Black Tree monitors. Other suitable substrates include soil, sphagnum moss, leaf litter or a combination of these. Cypress mulch looks nice and is able to hold moisture. A humid environment will benefit this tree monitor so the entire enclosure should be misted on a regular basis to keep the humidity up.
Being a small monitor, Varanus becarri should be offered prey items of suitable size. It is thought by some that these monitors have a hard time digesting prey covered with hair i.e. mice. This may be due to basking temperatures that are not high enough but I can't say this for sure. Since they do live most of their lives in the trees they may not encounter as many mammalian type prey as would be found on the ground and may not have evolved to digest hair as efficiently as some ground dwelling varanids. This is just a thought however.
It is important to offer a varied diet to Black Tree monitors. Acceptable prey items include crickets, roaches, mealworms, other insects (pesticide free), eggs, mouse fuzzies, rat pups and ground turkey. Some keepers also add a bit of canned cat food to the diet and have been successful in their breeding efforts. Note: Fresh water should be available at all times
Varanus becarri is a small monitor, relatively speaking. It is slender with long limbs and a long tail giving it a lanky look. It is not as bulky as other monitor species so even though it can reach lengths of 3-3.5 feet TL (Total Length) it won't look as big as a Savannah monitor of equal length. This is why I say it is a small monitor, relatively speaking. Even though a Black Tree monitor can reach 3.5 feet TL, up to 60-70% of that would be composed of prehensile tail. That means that a monitor that measures 3.5 feet TL will have a tail that is about 2.1 feet long!
Freshly imported Black Tree monitors can be very shy and skittish. They will need time, hiding places and good husbandry practices to help them acclimate to captivity. It is recommended that they be checked by a qualified vet for internal parasites and bacteria as soon as possible. Shipping usually places a lot of stress on these monitors and they tend to arrive in bad shape. Offer them water and mist the cage regularly to help re-hydrate them. They will hide much of the time at first but will eventually show themselves more often.
Defensive behaviours include biting, scratching and defecating. They have very sharp teeth and nails and use them well. The tail is not used as a weapon as it is in most other monitor species. There are many cases of Black Tree monitors becoming so well adjusted that they will accept food from their keeper and allow themselves to be stroked. Care should be taken when handling them because they are extremly fast and agile and can escape your grip if you are not careful.
My name is Michael Stefani, I live in the Chicago area of Illinois. This artical is based on my husbandry methods, that have lead to the successful breeding of my two female Varanus beccari. I have a 1.2 trio of Black Tree monitors that are housed together at all times. The temperature in their enclosure is 85 to 90 degrees ambiant, with basking sites well over 100 degress. Relative humidity is between 70 and 100%. To insure the high humidity level that these Varanids need to thrive, I use no subsrate in the enclosure, but instead the entire bottom is a reservoir. Complete with an artifical rain maker that rains on 30% of the enclosure .During my artificial dry season(approximately three months) the enclosure gets light spraying two to three times a week, in addition to cutting back my rain maker by several hours. During my wet season(approximately two months) the enclosure recieves heavy sprayingdaily, with an increase of the rain maker up to nine hours. This is when I see breeding activity.
To breed these monitors I believe a varied diet is very important. My Black Tree monitors are offered mainly insects (cricket's, roaches, ect) I also give them pink to fuzzy mice. For vitamin supplements I use only Sticky Tongue Farms MINER-ALL for indoor use. This stuff is great. My hubandry methods have lead to the successful breeding that hasresulted in six eggs and counting.