Resurrection
Play behaviour by captive tree monitors, Varanus macraei and Varanus prasinus
Play 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), 23-
26 °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.
Observations on Varanus macraei
Both specimens of V. macraei were repeatedly observed
engaging in focussed destructive behaviour involving the
leaves of plants for weeks or months after the plants were
added. The behaviour included initial investigation and then
removal of all or parts of individual leaves using mouth and
front limbs to tear. The leaf sections removed were often
transported some distance to a perch or hide where, using
mouth and forelimbs, they were systematically shredded and
then wiped in an exaggerated manner across rock work (Fig.
1 a). The fragments were typically not consumed (occasional,
apparently incidental, ingestion of small fragments was
observed), and once the leaf section is shredded, the lizards
typically returned to the plant to obtain another piece. The
behaviour was displayed at different times of day and was
not associated with the presence of food.
Observations on Varanus prasinus
Several juvenile V. prasinus were observed removing leaves
of Schefflera arboricola and Ficus benjamina and engaging in
destructive behaviour (Fig. 2 a-c). It is not known whether
these animals continued the behaviour past 1.5 years since
by that age they were transferred from the collection. The
behaviour was not observed in adult V. prasinus (n = 6) or V.
macraei (n = 3) maintained under similar conditions at Bristol
Zoo. Individuals investigated a leaf with tongue flicking before
removing it with their mouth, often shaking the head side to
side while pulling, and using forelimbs to assist if necessary.
On one occasion a freshly-fallen leaf was picked up from the
floor of the enclosure. The leaves were then transported to a
favoured perching area where the mouth and forelimbs were
used to bite and tear them apart, usually into two or three
pieces. The front limbs were used to hold leaves in position
to allow the animal to release the leaf from its jaws and
reposition its bite location and to hold the leaf in place while
biting/mouthing and pulling to assist in tearing. This posture
also allows the lizard to engage in forelimb raking, similar
to prey handling behaviours described in several species of
the Hapterosaurus subgenus by Greene (1986), Irwin (1996)
and Hartdegen (2000). Exaggerated wiping of the leaves
from side to side against the perch was also witnessed.
Occasionally the leaf would be accidently dropped to the floor
of the enclosure and the individual would retrieve it, usually
chasing after it as quickly as it could, and then returning to its
original position to continue the aforementioned behaviours.
One individual was observed collecting a second leaf with
mouth and forelimbs while keeping hold of another, where
the destructive behaviour described was exhibited on two
leaves at the same time. No attempts to consume any leaf
fragments were observed. The behaviour was not associated
with the presence of food and has been observed at different
times of day, both on feed and non-feed days alike.
Play behavior in captive tree monitors