Sweeney, Roger, Sekscienski, Stacey, and Maslanka, Mike. 2017. "Nutritional Analysis of Natural Fruit Items Consumed by Butaan (Varanus olivaceus) with Comparison to Commonly Used Captive Dietary Items." Herpetological Review, 48, (4) 787–791.
Varanus olivaceus (Hallowell 1859), known locally as the "Butaan," is a large monitor lizard species with a highly specialized frugivorous diet, and it is endemic to the Philippines (Auffenberg 1988; Bennett 2008, 2014). Adults may reach lengths up to 1.5 m, and weights exceeding 9 kg have been recorded (Auffenberg 1988). This species is currently listed as Vulnerable under the IUCN Red List criteria (Sy et al. 2009), based upon its extent of occurrence of less than 20,000 km² and area of occupancy of less than 2,000 km², with severely fragmented habitat across its range. Varanus olivaceus is threatened by habitat loss and fragmentation, through conversion of land to agricultural use, and logging operations. It is also threatened by hunting for food by local people and collection for the pet trade (Bennett 2008, 2014; Sy et al. 2009). Since the 2009 IUCN assessment was recorded, the range of this species has been reduced significantly because the northern extent of the population has now been reclassified as a distinct species, V. bitatawa (Welton et al. 2010, 2012), suggesting that the threatened status of V. olivaceus may be raised upon further review under IUCN threat criteria, given the resulting reduction in both the species' extent of occurrence and area of occupancy. This species is arboreal and has been recorded from both primary and secondary tropical moist forests, often with rocky outcrops or cliffs (Auffenburg 1988), but more recent information suggests it is more likely restricted to lowland forested areas (Bennett 2005). While the diet of juvenile animals contains a significant amount of animal matter in the form of snails and crabs, as they mature they transition to an obligate frugivorous diet (Bennett 2005, 2008, 2014), eating fruits of various trees including Pandanus, Canarium, Pinanga, Micrococos, Gnetum, and Ficus species, which is otherwise atypical for species of Varanus. A small number of North American zoos have kept captive specimens of V. olivaceus in recent decades, including Dallas Zoo, Oklahoma City Zoo, and Riverbanks Zoo (Card 1994, 1995). This species has proved challenging to maintain long-term and breed in zoological collections (Bennett 1998; Yuyek 2012). The challenges associated with successfully maintaining this species in zoos had resulted in V. olicaceus not being recommended for population management within the Association of Zoos & Aquariums – Lizard Taxon Advisory Group, Regional Collection Plan (2013), despite the species' strong conservation importance. At the time of writing, two zoos in North America currently maintain adult wild-caught V. olivaceus in their collections. One of these institutions, the Los Angeles Zoo and Botanical Gardens, has recently been able to achieve successful and consistent breeding success (Recchio 2016), and this has made it possible for several additional North American Zoos to acquire zoobred specimens. The successful breeding at Los Angeles Zoo is the first recorded in the United States. Previously, in January 1993 the Dallas Zoo hatched a single V. olicaceus from a clutch of eggs, but it did not survive past 24 h (Card 1995). There is also a confirmed report of a successful breeding having been achieved in the Philippines at the Avilon Montalban Zoological Park (Yuyek 2012). Despite recent breeding success, achieving expected longevity of captive specimens and replicating captive reproduction more widely is still challenging for this species. An important research focus with V. olivaceus in zoological facilities is the need for continuing refinement of the captive diet. Current diets of captive V. olivaceus in North America include a high percentage of fruit such as cantaloupe, grapes, dates, apples, papaya, bananas, and figs (Recchio 2016). It is unknown if the nutritional compositions of these domestically-cultivated fruits mimic those of the specific fruits eaten by this species in the wild. The primary goal of this study was to increase knowledge about the baseline nutritional needs of this species. Fruit samples of species that are known to comprise a high proportion of the natural diet of V. olivaceus were collected and a proximate nutritional analysis of these wild fruit samples was conducted. Secondary goals included comparing the nutritional values for wild fruits with known values for domestic fruits currently offered to V. olivaceus in captivity, identifying potential field sites and logistical information for future related project work, and continuing to strengthen relationships between AZA and partner organizations in the Philippines, exploring further opportunities for research and conservation.
