Mugger crocodile preys on mysterious tortoise



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By Ifham Nizam


Ecologist, Mahesh De Silva, Herpetologists, Thasun Amarasinghe and Suranjan Karunarathna who is also a member of Species Survival Commission Crocodile specialist group of the IUCN International, recently observed an unusual adult tortoise at 11.40 a.m. in the Bundala National Park.


According to them, the animal most closely fit into the description of the Star tortoise and had a total carapace length of around 30 cm. The weather was bright and sunny but the surrounding water bodies were full due to five days of heavy rain.


The soil was dry. The tortoise was first seen from a distance of 20 m. and it was about two meters from the tank’s edge. This particular tank known as `Palugaswala (Pathiraja road)’ is about 50 m long and 30 m wide and elliptic in shape.


De Silva says the tortoise was feeding on vegetation and was looking towards the tank and around 11.50 a.m. a Mugger crocodile,-total length about 2.5 m- appeared at the water surface about four meters away from the tortoise and two meters away from the bank. Within three minutes the crocodile edged slowly towards the land and suddenly grabbed the tortoise. The crocodile caught the tortoise from its anterior carapace dorso-ventrally.


"Just after catching the tortoise, the crocodile went back to the water about 10 m from the bank with the tortoise in its mouth. Then the crocodile dived and disappeared. After about 30 minutes, at 12.25 p.m. the tortoise re-surfaced.


The tortoise appeared weak, possibly injured by the crocodile attack and moved slowly towards the land. The movement was more floating than active swimming. At 12.31 p.m. the tortoise reached the bank without seemingly attracting the crocodile. Suddenly the crocodile re-appeared at the bank, from underneath the water,"


De Silva went on say that the Mugger approached the tortoise quickly and tried to grab virtually the entire tortoise a number of times. However, it failed in all attempts, due to the movements of the tortoise and the shape of the carapace. The tortoise was turned upside down and it tried to turn but failed due to the mud on the bank.


"Surprisingly, considering the crocodile’s huge jaws and powerful bites, we did not observe any damage to the carapace of the tortoise. The crocodile then moved back about 50 cm and remained still for a few seconds," he added.


It then jumped forward and this time grabbed the tortoise from one end of the carapace. After this the crocodile went back into the water about 10 m from the bank, waited for a few minutes on the surface and then dived and disappeared at 12.34 pm. Mahesh and his team waited there until 1.22 p.m. but did not see either the crocodile or the tortoise again.


Suranjan Karunarathne of the Nature Exploration & Education Team, says the Mugger crocodile is the second largest reptile in Sri Lanka, living in freshwater streams, rivers, canals, tanks and even in hyper-saline estuaries.


Currently, the Mugger is categorized as a vulnerable species and protected by the Fauna and Flora protection ordinance (Act no: 44 of 1964) in Sri Lanka. The Mugger crocodile is also found in India, Pakistan, Bangladesh, Nepal and Iran.


Muggers take a wide range of prey. The principal diet of the species is insects, crabs, shrimps, fish, frogs, terrapins, other reptiles, small mammals, monkeys, deer, sambars, buffalos, and occasionally humans.


According to previous research, Star Tortoises were considered as ones who could not swim or dive in water. The radiated tortoise in this instance coming towards the tank and feeding on the vegetation at noon in the hot climate of Bundala National Park is uncommon. The more usual active foraging times of the land tortoise are in the morning (6:00 to 8:00 am) and at dusk when the sun is not hot. Possibly it could have come to drink water.


Researchers Thasun Amarasinghe and his wife Komunitas Konservasi Alam Tanah Timur from Indonesia, says the distinct carapace, body morphology and colouration of this particular tortoise was quite different to the common Star tortoise, which is the native species widely distributed in the dry zone lowlands of Sri Lanka and common in the Bundala National Park.


Based on the photograph many herpetologists considered this animal as Leopard tortoise. It is also possible that it may be an aberrant form of Star tortoise or possibly a different foreign species.


Scanning through the available literature they found an interesting report by Amyrald Haly (the first Director of the Colombo Museum) of purchasing a ‘star tortoise’ from Wellawatte (Colombo). The person who had collected it stated that it was not the first time he had seen specimens of this particular species.


Haly assumed that this could have been a foreign species that had escaped from captivity or been released after being kept for some time. Haly also reported of securing a Star Tortoise from a grass field in Cinnamon Gardens (virtually Central Colombo).


This could have been an escaped pet or one that had been brought and released after some time.


Mahesh says: "We could assume that Europeans who lived in Sri Lanka during the colonial period (up to 1948) would have brought pet tortoises and released them after some time. We have to consider another important fact. Many pet traders in the country have been importing the American Red-eared Slider which is considered as one of the top invaders into many ecosystems in the world and is now found in water bodies in Colombo and its suburbs."


Thus, he says there is a possibility that some pet traders could have also imported other radiated tortoises. However, due to legal actions taken by the Department of Wildlife Conservation, many people have handed over their pet Star tortoise collections to the Department of National Zoological Gardens or released them in various parks or forests.


Researchers say it is highly possible that there could be some exotic radiated tortoises in the wild in Sri Lanka. As regards Star tortoise, recent molecular work on it from the Indian subcontinent has shown a strong genetic diversity.


They recommend that a molecular study of the Sri Lankan Star tortoise from the south, east, north- central, north-western and the north of the country should be conducted.


 
 
 
 
 
 
 
 
 
 
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