(Monitor)ing the Breeding of Black Tree Monitors

The Oklahoma City Zoo and Botanical Garden recently welcomed four black tree monitor hatchlings; the first for the Zoo in several years. The Zoo participates in the Association of Zoos and Aquariums (AZA) Species Survival Plan® (SSP) for the Black Tree Monitor, a lizard species listed as near threatened by the International Union for Conservation of Nature (IUCN).  

Black tree monitors are found exclusively on Aru island off the west coast of New Guinea. This species gets its name from the solid black scales that cover the entire body, which help conceal them from predators. This three-foot long monitor species possesses a prehensile tail, which can be twice the length of the rest of the body, and long, sharp nails that allow it to strongly grip branches as it moves through the trees. 

Creating a successful breeding environment for the two adult black tree monitors at the Zoo required the herpetology care team to incorporate specific elements inside their habitat at the Herpetarium. Some of these elements included adding live plants and installing a misting system. To start, dense foliage featuring large climbing branches for the two monitors to climb on were added. Then, the misting system was set up to simulate the rainy season found in the natural environment of the black tree monitor. The misting system in combination with natural landscaping helped to maintain proper humidity inside the habitat and to encourage breeding behaviors.  

The herpetology team at the Zoo conducted introductions between the two adult monitors prior to placing them into their specialized environment. The monitors then began to spend time together in this new habitat, and caretakers observed both animals closely for signs of breeding, which occurred within days. Once breeding was observed, the care team relocated the possibly gravid female (i.e., female reptile carrying eggs or young) to a private habitat behind the scenes that contained a nesting or egg-laying box. This ensured that the female had more privacy and that caretakers would have the ability to locate the eggs soon after they were deposited.  

When caretakers found the eggs, they were immediately placed inside an incubator, and the female was returned to her habitat. It took roughly 164 days for the monitor eggs to hatch in the incubator that was set at 86 degrees Fahrenheit. Four out of five eggs hatched, and caretakers were thrilled to witness the event as each hatchling began breaking through the egg - called pipping. Hatchling coloration is not solid black like the adults but consists of green spots or bands that fade as they get older. The hatchlings are healthy and growing. They will remain at the Zoo for a few months before venturing to other AZA organizations to participate in the SSP.  

The black tree monitor hatchlings at the Zoo are currently learning to hunt and find food. They are eating a variety of proteins, such as crickets, roaches, mealworms, pinky mice and fish. Caretakers have found that each hatchling has its own personality. Similar to human babies, the hatchlings are picky about what food items they prefer to consume, so their diets are adjusted accordingly to ensure proper nutrition.  

Because black tree monitor populations are declining in the wild due to deforestation and the international pet trade, the Zoo is committed to the conservation of the species through AZA’s SSP program. SSP programs are collaborative science-based management programs developed by the AZA to oversee breeding and sustainability of select animal species within AZA-member zoos and aquariums. Several of these programs also enhance conservation efforts of these species in the wild.. 

The curious and intelligent nature of the Zoo’s black tree monitor lizards have charmed the hearts of their care team and Zoo guests. The hatchlings will remain behind the scenes; however, Zoo guests can see the two adult black tree monitor parents where they reside in the Herpetarium building. 

- Stephany Hernandez, herpetologist  

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