<em>By Robert W. Mendyk
Supervisor of Animal Husbandry and Exhibits
Center for Science Teaching and Learning
Rockville Centre, NY
<a href="mailto:odatriad@yahoo.com"> odatriad@yahoo.com</a></em>

<strong>Introduction</strong>

Mendyk and Horn (2011) recently described an insightful foraging behavior in the black tree monitor, (<em>Varanus beccarii</em>), in which the lizards use highly coordinated, reaching forelimb movements to extract prey from inside tree holes that are too narrow to enter with the head and jaws. Analogous to a foraging technique used by the Aye-aye (<em>Daubentonia madagascariensis</em>) to extract insect larvae from inside trees (e.g., Erickson, 1994), this behavior in the black tree monitor requires complex problem solving abilities, concentration, and fine motor coordination, thus making it a worthy candidate for exploring its application in monitor lizard husbandry as enrichment (Mendyk and Horn, 2011). This article briefly describes two simplistic enrichment devices for use in zoos and related facilities which promote extractive foraging in arboreal monitor lizards of the (<em>Varanus prasinus</em>) species complex.

<strong>Materials and Methods</strong>

<span style="text-decoration: underline;">Drilled tree trunk</span>

Modifying the original experimental apparatus described by Mendyk and Horn (2011) to offer greater foraging opportunities, 15 holes of varying depths (15 to 75 mm) and diameters (13 to 50 mm) were drilled into a 13 cm thick tree trunk placed inside the terrarium of an adult male black tree monitor (Fig. 1). Some of the holes were wide enough for the monitor to insert its head into, whereas others were not. Mealworms (<em>Zophobas morio</em>), crickets, cockroaches (<em>Blaptica dubia</em>), and neonatal mice were periodically offered to the monitor by randomly placing prey items inside different holes within the trunk.

<span style="text-decoration: underline;">Transparent acrylic cube</span>

As a way of promoting further mental and physical stimulation, a transparent cube measuring 512 cm3 was constructed from 6 mm thick acrylic (Fig. 2). Two small 5 mm holes were drilled into five of the six sides to allow for scent detection of prey. A 15 mm wide hole was drilled centrally in the sixth side, which was fastened to the cube with transparent tape allowing easy keeper access to its contents. Neonatal mice or mealworms were periodically placed inside the cube atop the terrarium substrate for the monitor to retrieve with its forelimbs.

<img class="alignnone size-large wp-image-2268" title="mendyk-4" src="http://aecetia.net/gws/aazk/wp-content/uploads/mendyk-4-1024x768.jpg" alt="mendyk-4" width="614" height="461" />

The feeder cube gets some heavy use, which includes the monitor pushing the cube around the exhibit.  <em>Photo by Robert W. Mendyk.</em>
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<strong>Results and Discussion</strong>

The common practice of feeding monitor lizards at the same location within the enclosure day after day can potentially produce two undesirable conditioned responses. First, it may lead to keeper-directed feeding aggression which can be potentially dangerous for keepers, especially when dealing with larger species. Alternatively, it can produce lethargic animals that sit and wait to be hand-fed rather than actively pursue and search for food in their enclosure as they normally would in the wild. In this study, feeding the black tree monitor at different locations within its enclosure and alternating usage of the drilled tree trunk as well as each individual tree hole has markedly reduced feeding…

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