Study sites For the present study, field work was carried out from October - December 2014 and from June - December 2016 at Karamjal ecotourism spot and adjacent areas . The sites are situated under Chadpai range of Sundarban Forest Department, Bagherhat, Bangladesh. The Crocodile & Deer Breeding Center is the main attraction of Karamjal. The jungle is surrounded by a number of county villages (Herbaria, Laodove, Baniashanta and Koilashgang). Sunderbans is a very humid area, due to its proximity to the Bay of Bengal, and it is usually very hot during the summer, when the mercury can soar up to 40°C. On the other hand, winters in the area are quite cold, with temperatures droping to around 9.2°C. Sunderbans receives heavy rainfall, from mid-June to mid-September. The habitat types of the study area are categorized as (1) mangroves, dominated by Heritiera fomes, Excoecaria agallocha, and Sonneratia apetala; (2) grasslands, typically with Imperata cylindrica, Acrostichum aureum, Myriostachya wightiana; (3) mudflats, including sandy tidal flats and beaches; (4) transitional zones between these three habitats, usually with few trees, sometimes with reeds; and (5) deep water, including rivers and estuaries, covering most of the sanctuary (Khan, 2005). Recent hydrological connectivity of the aquatic ecosystems in the Sundarbans Delta, makes them highly sensitive to a broad range of anthropogenic activities (Bautista Rahman, 2015). A variety of methods were employed to conduct this research. The Visual Encounter Survey method (Heyer et al., 1995) was followed for observing and counting the study lizards. These surveys generally comprised walking through a forest trail or specific transect line to check for sheltering animals. The number of observed animals and sighting time was then recorded in a data sheet. The activity patterns of water monitors were studied by focal sampling method in which data was recorded continuously during a certain period. Focal sampling means observing one individual for a specified amount of time and recording all instances of its behavior (Altmann, 1974; Slater, 1978; Martin Bateson, 1986). Ideally, the choice of focal individual is determined prior to the observation session (Altmann, 1974). The observation was done daily in every 1 week of each month from morning to evening. During this time, all the activities that the focal animal performs were recorded, while the activities of any other active animal were not recorded at the same time. When a focal individual became not visible, we started searching for another active animal, and after finding it we started to record all its behavioral activities. To avoid influencing their behavior, the animals were followed on foot and observed from hidden points. The activities of water monitors were recorded in six distinct categories as feeding (any activity of an animal that is directed toward the procurement of nutrients), foraging (visits different potential food sources in search of food by walking, swimming or by climbing), resting (when an individual becomes inactive and does not move much), basking (that is basically sunbathing or thermoregulatory behavior, occurring especially during the cold season to heat-up the body, conflicting (when an individual competes or engages in clash with another individual of the same or different species for food, mate or territory), and others (combination of some miscellaneous minor activities like hiding, escaping and courtship that were seen or observed rarely during field study). Proportion of time spent in different activities or behavior was calculated by the equation: Tf = (nf × 100) ÷ N (Gupta' Kumar, 1994). Where, Tf = time spent on a specific behavior as percentage (%) of total active period; nf = amount of time spent for showing a specific behavior; and N = total amount of time spent for all behavior. Besides field observation and interview with local people, stomach content samples were also taken from the fieldcaptured V. salvator to examine its diet in this study. Field-captured V. salvator were stomach-flushed to collect the dietary items (Mayes et al., 2005). We inserted a plastic tube (approximately 1 cm in diameter and 1 m in length) down the esophagus past the glottis until the distal end of the stomach was reached. A hand pump was used to pump approximately 500-600 ml of water through the tube into the stomach. Vomited stomach contents flushed from individuals were collected in a bowl-shaped utensil. Water was pumped into each individual 2 to 3 times before the plastic tubing was removed. The collected stomach contents were then stored in 70% ethanol. Then, stored stomach contents were later dried for a specific period and identified the prey group. The proportion in the diet represented by each prey group was calculated by using the previsous equation Tf = (nf x 100) / N (Gupta Kumar, 1994), where Tf = proportion of a specific prey group as % of total stomach content; nf = number of a specific prey group; and N = total prey group recorded from the stomach.