Habitat preference and feeding ecology of the bengal monitor (Varanus bengalensis) in Natore, Bangladesh

The peculiarity of the preferences of the Bengal lizards to live in microenvironment with dense and dry ground. Characteristics of building nests adjacent to water bodies. The choice of grasshoppers as a diet instead of hunting for other varieties.

Рубрика Иностранные языки и языкознание
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Язык английский
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Казанский федеральный университет

ПРЕДПОЧТИТЕЛЬНАЯ СРЕДА ОБИТАНИЯ И ЭКОЛОГИЯ ПИТАНИЯ БЕНГАЛЬСКОГО ВАРАНА (VARANUS BENGALENSIS) В НАТОРЕ, БАНГЛАДЕШ

Рахман К.М.

Bengal Monitor (Varanus bengalensis) (Daudin, 1802) [1] is a very common monitor lizard species widely distributed over South Asia including Bangladesh [2, 3, 4]. Bengal monitors are used to much larger geographic range compared to other varanids lizards. An adult Bengal Monitor is about 175 cm with a snout-to-vent length (SVL) of which tail is 100 cm. Males are larger than the female and a heavy individual may weigh nearly 7.2 kg [5]. Bengal monitors are considered as least concerned species according to the IUCN red list of threatened species though their population is decreasing [6].

Our study area Natore is a northern district of Bangladesh which is situated between latitude of 24° 24? 28.58” N and longitude of 88° 58? 29.61” E with an average elevation of 23.26 m. It is about 204 km north-west of Dhaka City, Under Rajshahi Division. The district is considered as the diverse habitats for different types of flora and fauna. There are forest patches, woodlands, bushy jungle, grasslands, cultivated lands and many temporary and permanent waterbodies are present. Natore is unique form other district of Bangladesh from biological point of view because of the presence of the largest Chalan Beel (natural water bodies) which support different types of Biodiversity.

Methods and Materials

For collecting data, we spent more than 2 month October- December 2014 in the field. We used visual encounter survey (VES) for the observation of Monitor lizard species. We studied distribution of species in different microhabitat using randomized VES and habitat ecology by using intensive time constrained VES. We surveyed all of the study area by walking and observing likely habitat for the species to assess the distribution. We conducted the survey four days in October, 3 days in November and four days in August and each day we spend six hours that means we studied the species a total of 66 survey hours. During field study we also talked with the local peoples. We documented the killing of the species and we also took the measurement of the dead species. We also tried to find out the causes of the killing, spot of the killing. For present study we carried and used following types of equipment: Data sheet, pen, pencil, GPS unit, slide calipers, scale, savlon, cotton, camera etc.

Ethical approval: All of the data were collected during the study period by the proper approval of Bangladesh forest department. During this study no animals were harmed or injured intentionally or unintentionally and we followed all of the code, conduct and legislation for the care and use of animal for scientific purposes.

Results and Discussion

During this study, we observed 16 individuals of Varanus bengalensis species. By talking with the local peoples we also informed that the species occurs in all parts of the study area. The species richness of the Bengal Monitor decreasing day by day at an alarming rate because of the interaction with the local peoples and lack of sufficient knowledge of the villagers about the beneficial role of species. We found total 5 dead species during this study and all of the species died or more precisely had been killed by the local inhabitants without any reasons. It is documented that most of the cases children were responsible for more than 60% killing and 20% were killed because of fishing net used by the local fisher man. We documented 20% killing of Bengal Monitor during the clash between Domestic dog (Canis sp) and Bengal monitor Species. Local peoples told us that because of this clash every year lot of Monitor lizard species become injured and died.

Our study area was limited to the dry land with busy vegetation from the wet lands (irrigated areas, ponds, canal, beels etc.) and we surveyed each of the habitat types for 11 days to find out the feeding ecology and habitat preference of Varanus bengalensis. We observed 16 Bengal Monitor species during the study period; 10 during the distribution study and 6 during habitat separation study. Bengal Monitors showed considerable habitat preference during present study survey. Among the found 16 number of Varanus bengalensis, 56.25% used dry land habitat with bushy vegetation, 12.50% paddy fields, 6.25% ponds, 6.25% canals and 18.75% beels as their microhabitat (figure 1). But in our study we observed that most of Bengal monitors species prefer to make their nest slope of the dike adjacent to the waterbodies. We found total 7 nest of them 5 nests were adjacent to the waterbodies and 2 nests were found slope of the road.

Bengal Monitor tend to active whole days with different activities including feeding. There were two peaks of feeding time were identified throughout the day one during morning from 6:00 AM to 9:00 AM and another during afternoon from 3:00 PM to 5:00 PM. The diet of Bengal Monitor comprises of Insects, fishes, frogs, mouse, crustaceans, young and eggs of birds, vegetables and fruits matter (Table 1).

Table 1 - Diet composition of Varanus bengalensis in the study area

Nine different prey groups were identified during this study and all of these prey groups provide food for the Monitor throughout the year. Grasshoppers constitute a major portion of the Bengal Monitor diet (24%). The Bengal Monitors avoid foods which are bigger than themselves and which they couldn't overpower.

Bengal monitors are actually solitary and terrestrial animal but sometimes they are seen on trees [7]. Unlike the other varanid lizards, Bengal monitors have the capabilities to adopt with diverse form of habitat, from desert areas to floodplains, scrubland to forests, at moderate elevations (Auffenberg 1994, Pianka 2004) [8, 9]. Bengal monitor have much larger geographic range, they inhabit river valleys in eastern Iran, Afghanistan and western Pakistan (Luxmoore & Groombridge 1990) [10]. It is similarly ubiquitous in India, Nepal, Sri Lanka, Bangladesh and Burma, found from desert fringes to rainforests, but is most common in farmlands and dry, open forests (Deraniyagala 1931, Pianka 1995) [11, 12]. It can also inhabit agricultural areas (Auffenberg 1994) [13]. So, our present study result also supports the result of Auffenberg and Pianka because in our study site their presence was also observed almost all kinds of microhabitat types from dry land to waterbodies including agricultural areas. Bangladesh is mainly a subtropical country with mixed evergreen and deciduous forest types and Bengal monitor widely distributed over almost all of the forest types. Auffenberg 1994 also mentioned about that the most common tropical forest habitat for Bengal monitors are deciduous, semi-deciduous, evergreen tropical forests, and thornbrush [13].

The Bengal monitors are almost strictly carnivorous. They consume almost everything that is smaller than themselves and that they can easily overpower (Auffenberg 1994) [13]. But in our study we have seen Bengal monitors eating waste vegetables and fruits matter thrown from the kitchen of the villagers. In a study Rahman et al 2015 also mentioned about the vegetables and fruit matters as Bengal monitors diet. Auffenberg 1994 in his study mentioned roughly 200 prey species [13]. In our study we documented only 9 different prey groups. We couldn't find out a vast list of prey groups because of mainly our study site was only limited to Natore and our field observation period was also very short.

Conclusion

According to IUCN red list Varanus bengalensis still considered as a least concern species but this environmental friendly species is decreasing day by day in number at an alarming rate. Habitat destruction and fragmentation, illegal trade, insecticide use in the farm lands, unconsciousness of the local people are the most common causes of their number loss. So, proper initiatives immediately should be taken nationally and internationally to protect this important lizard species.

Competing Interests Authors have declared that no competing interests exist. lizard ground grasshopper hunting

Abbreviations

SVL: Snout-to-Vent Length, IUCN: International Union for Conservation of Nature, VES :Visual Encounter Survey, GPS: Global Positioning System.

References

1. Auffenberg W. Research on monitor lizards. Tiger Paper. 1979;6(4):20-21.

2. Das I. Biodiversity and Biogeography of the herpetofauna of Southern Asia. 2001;1-38. In.

3. Das I. Distribution and maps of monitor lizards of India. J Madras Crocole Bank. 1983;1(22).

4. Khan M.M.H. Protected Areas of Bangladesh - A Guide to Wildlife. Nishorgo Program, Wildlife Management and Nature Conservation Circle, Bangladesh Forest Department; 2008;1(230).

5. Zug G.R, Win H, Thin T, Min TZ, Lhon WZ, Kyaw K. Herpetofauna of the Chatthin Wildlife Sanctuary, north-central Myanmar with preliminary observations of their natural history. Hamadryad. 1998;23(2): 111-120.

6. Auffenberg W. Research on monitor lizards. Tiger Paper. 1979;6(4):20-21.

7. Pianka E.R. Varanoid Lizards of the World: Varanus bengalensis. Indiana University Press. 2004;156-160.

8. Luxmoore R. & Groombridge B. Asian Monitor Lizards - A Review of Distribution, Status, Exploitation and Trade for Four Selected Species. World Conservation Monitoring Centre (WCMC), Cambridge, UK.1990; 195 pp.

9. Deraniyagala, P.E.P. Some Ceylon lizards. Spol. Zeylon.1931a;16:139-80

10. Pianka, E. R. 1995. Review: Lizards observed. Science, 268/5217:1636

11. Auffenberg & Walter. The Bengal Monitor. University Press of Florida. 1994;494. ISBN0813012953.

Annotation

The study was conducted between October and December 2014 in the district of Natore, Bangladesh by following visual encounter survey method. Most of the Bengal monitor (56.25%) prefer to live in the microhabitat of bushy dry land but they build their nest most of the cases adjacent to the waterbodies. They consume a vast list of prey groups as their diet but they choose grasshoppers as diet in highest proportion (24%) than the others prey species. Sometimes they consume waste vegetables and fruits matter also. Maximum feeding activity was recorded in the morning from 6:00 AM to 9:00 AM and during afternoon from 3:00 PM to 5:00 PM.

Keywords: Bengal Monitor, diet, habitat.

Исследование проводилось в период с октября по декабрь 2014 года в районе Натор, Бангладеш методом визуального наблюдения. Большая часть Бенгальских варанов (56.25%) предпочитает жить в микросреде с густой и сухой землей, но в большинстве случаев они строят гнезда, прилегающие к водным объектам. Их список добычи обширен, но в большинстве случаев они выбирают кузнечиков в качестве рациона (24%), вместо охоты на другие разновидности. Иногда они употребляют в пищу овощи и фрукты, которые также им необходимы. Максимальный пик деятельности, связанный с кормлением и добычей пищи, зарегистрирован утром с 6:00 до 9:00 и в течение дня с 15:00 до 17:00.

Ключевые слова: Бенгальский варан, диета, среда обитания.

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