Fancy Frugivores

New to our Herpetarium, the two young and precarious Gray’s monitor lizards (Varanus olivaceus) are two of only 14 that are currently living in North American zoos.  

Discovered in 1845, by John E. Gray, this lizard species was lost to science for the following 130 years until Walter Auffenberg discovered a specimen in the United States Museum of Natural History, one of only three documented since 1845. Eight years later, he undertook an intense 22 month study of the ecology and behavior of these animals in their natural habitat. In the wild, these monitor lizards can only be found in the tropical moist forests of the Philippine Islands. Related to the infamous Komodo dragon, this species is almost exclusively arboreal and will spend most of its time in the treetops or on rocky outcrops. Reaching lengths of up to 5 feet, it is one of only three species ofmonitor lizards out of 79 worldwide that eats fruit. 

The Gray’s monitor lizard is listed as Vulnerable by the IUCN (International Union for Conservation of Nature and Natural Resources) which means that populations are facing a high risk of extinction in the wild. This species is threatened by habitat loss and fragmentation due to agricultural use and logging operations. It is also collected for the pet trade and hunted for food by the local people. 

The most striking aspect of the biology of this species is that unlike most other adultmonitor lizards which are carnivorous i.e. meat eaters, these “tree dragons” are primarily fruit eaters or “frugivores”. In their native habitat, adult Gray’s monitors eat only a handful of fruit species such as Pandanus and Canarium, all of which have a unique nutritional footprint. Young lizards will eat more insects and snails than fruit but quickly switch over to primarily fruit after a few years. As with all of our zoo animals, it is important that we insure proper nutrition and therefore continue to research best dietary options for these lizards. For almost ten years, the Oklahoma City Zoo has housed adult lizards behind the scenes and collaborated with other partners such as the Los Angeles Zoo, Dallas Zoo, and most recently the Virginia Zoo to provide the best care and nutrition for these one-of-a-kind lizards.

A few years ago, I had the idea of comparing nutritional value of the fruits that thesemonitors were eating in the wild to the fruit types that we were feeding in zoo settings to see if there was anything lacking in the diets of the zoo housed animals. So, one day during a phone call to Roger Sweeney from the Virginia Zoo on a completely different subject, I discovered that Roger had a life-long interest in the wildlife of the Philippines and had already created solid collaborative partnerships within the country. I then peaked his interest about the Gray’s monitor lizard and my idea and after further conversations, he decided that this information could be easily gathered during one of his trips to the Philippines. In 2015, through its Conservation Action Now grant program, the Oklahoma City Zoo funded Roger Sweeney from the Virginia Zoo to travel to the Philippines to collect known wild fruit types for nutritional analysis. After collecting the fruit, Roger worked with the University of the Philippines and Dr. Mike Maslanka from the National Zoological Park in Washington D.C, to analyze fresh fruit samples so that we could compare the nutritional makeup of wild fruit diets to fruits that we are currently feeding to our Zoo housed lizards. The results showed that there were certain fruits, such as papaya, that had a higher protein and fiber content than some of the other fruits offered, such as cantaloupe, etc. and that in the wild, lizards were choosing fruits with higher protein and fiber content. By studying and using the results of the analysis, we were able to fine tune our Gray’s monitors’ diet. There is still much to learn about this fascinating frugivore and the Oklahoma City Zoo is excited to be a part of the discovery process with the future goals of revealing more unique aspects of the ecology and behavior of this species. 

– Stacey Sekscienski, zoological curator

Photo: Rae Karpinski, senior animal caretaker 

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