Play behaviour by captive tree monitors, Varanus macraei and Varanus prasinus

P describes suites of behaviour that are perceived as ‘non-serious’. Play has proven to be difficult to define although there have been many attempts to do so (see Burghardt, 2014). Initially, play was thought to be limited to mammals and birds, but efforts to define it more objectively have led to the identification of play in a variety of other taxa as diverse as octopodes (Kuba et al., 2006), fish (Burghardt et al., 2015), and reptiles including monitor lizards (e.g. Hill, 1946), turtles (Burghardt et al., 1996; Kramer & Burghardt, 1998) and crocodilians (Lazell & Spitzer, 1977; Dinets, 2015). The widely accepted definition of play is ‘repeated, seemingly non-functional behaviour differing from more adaptive versions structurally, contextually, or developmentally, and initiated when the animal is in a relaxed, unstimulating, or low stress setting’ (Burghardt, 2014). Here we report the play behaviour of two species of monitor in captivity, Varanus macraei at ZSL London Zoo (Zoological Society of London) and Varanus prasinus at Bristol Zoo (Bristol Zoological Society). At ZSL London Zoo, observations were made on a pair of adult captive-bred blue tree monitors (V. macraei) aged 6 (female) and 7.5 (male) years. The animals were housed in a 3x2x1.5 m enclosure with a heterogenous structure including branches and artificial rockwork, a waterfall and a naturalistic substrate comprising layers of humus and leaf litter. Heating (mercury vapour lamps; Arcadia/Osram) and lighting (T5 UVB emitting fluorescent lamps; Arcadia Reptile) arrays provided an ambient temperature gradient from 25-28 °C (day), 2326 °C (night) and a diurnal basking zone with temperatures between 39-43 °C and a maximum UVi of 5, in accordance with best husbandry practices for the species (Ziegler et al., 2009). The animals were fed a variety of invertebrate and vertebrate prey; these were generally broadcast in the enclosure to allow the animals to engage in natural hunting and feeding behaviour. The animals were also target-trained using operant conditioning with food items as a reward. The enclosure had been repeatedly planted with a variety of live plants, especially Scindapsus and Philodendron, in order to increase structural and environmental complexity, as well as for aesthetic appeal to the public. At Bristol Zoo, juvenile (0.5-1.5 years), captive-bred V. prasinus were reared in custom glass-fronted fibreglass enclosures measuring 60x60x70 cm. Enclosures are furnished with live plants (e.g. Ficus sp., Schefflera arboricola, Scindapsus sp.), branches, cork bark tubes and damp refugia. The substrate consisted of humus and leaf litter and water was provided with a small 10 cm water bowl. Lighting (T5 UVB emitting fluorescent lamps, Arcadia Reptile; T5 6500K lamps, Philips) and heating (75 W halogen bulbs, Sylvania/Osram) provided ambient temperatures of 27-31 °C (day) and 24-26 °C (night), a basking site of 38-40 °C with a maximum UVi of 6.0, and a photoperiod of 12:12. They were fed four times a week on a variety of insect prey that were usually broadcast in the enclosure.