Brumation of the clouded monitor lizard Varanus nebulosus in north-eastern Thailand

Abstract

The clouded monitor lizard (Varanus nebulosus), is a semi arboreal lizard widely distributed throughout much of South and Southeast Asia. Despite its wide distribution there is almost nothing known about the ecology of this species. During the course of an 11-month radio telemetry study, in a reserve with a tropical savannah climate (Köppen Aw), we made the first records of brumation in this monitor lizard. This contrasts with earlier reports of the same species in a tropical monsoon climate (Köppen Am) where no brumation was recorded. We successfully tracked 10 individuals throughout their inactive period and found that seven of the monitors selected tree hollows within the endangered Shorea henryana tree. All tree hollows selected faced between the east and south cardinal points (90°-180°). The average brumation period was 100 days (range 86-113 days, standard deviation - 10.7), beginning in November at a time of falling temperatures and humidities and ending in early March when these variables had been restored. Eight of the 10 monitors basked partially or completely out of their shelters on multiple occasions. Of those eight monitors, two individuals moved between shelters during brumation after an extended period in one location. Our observations provide insight into the relationship between V. nebulosus and the tree S.henryana, in the dry evergreen forests of north-eastern Thailand. Future research should investigate how this tree will be affected by climate change in the coming decades and what that could mean for the future persistence of the clouded monitors that appear to rely on it.