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Special Feature 2006:

A trip to a temple pit viper population in the vicinity of Medan, North Sumatra

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Medan , the provincial capital of Northern Sumatra , is a bustling city of over 2 million inhabitants and a booming commercial centre for the region's huge oil and agribusiness. Oil palm plantations, rubber, cocoa, rice and other crops dominate the landscape. There is little natural forest left, and the area around the famous lake Toba has been denuded by paper factories.

Given these circumstances, I was not expecting any exciting location to observe Wagler's vipers in the wild. However, fortunately, my view proved to be completely wrong. Thanks to local friends and farmers I was able to witness one of the most dense populations of T. wagleri I have ever seen. I will not mention the exact location here to protect the animals. However, similar habitats are still abundant in the vicinity of Medan, in particular, in the forests that form the edge of the Karo plateau southwest of the city.

I had already spent numerous frustrating hours of roaming around in potential habitats, e.g. in the Sibolangit Botanical Garden, around Lake Toba and even in Gunung Leuser National Park. The forests around Berastagi are also beautiful, but probably too high above sea level, over 1000 m, to host temple pit vipers.

As it always comes with Wagleris in the wild (see my notes on Templer Park), you have to look in the backyard of a house, or a parking area of a highway bordering forest to observe them. I exaggerate, but there is some truth in it.

The location I would like to show you here is a river valley that is used by smallholder farmers to grow cocoa, rice and various fruits of the region, like guava, pineapple, sugar palm etc. The slopes of the valley show dense primary and secondary growth lowland jungle. The climate is extremely moist, as indicated by abundant mosses and lichens on trees and on the ground. Because T. wagleri is so abundant in this place, I think the name 'valley of temple pit viper' would be a suitable one.

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A fish pond and rice terraces used by farmers, bordered by lowland jungle. Nipa palms (Nypa fruticans) can be also seen in the center.

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Although the above habitat looked really inviting to check for Wagleris, I did not have to venture too far from the road as the animals flocked the cocoa plantations and gardens of the local farmers. In fact, this snake is so abundant here that farmers observe it on a daily basis. And they often kill it.

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Farmers' houses are surrounded by numerous trees, often fruit trees. The tree seen in the foreground was inhabitated by temple pit vipers.

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In a period of a five days, I observed eight Wagleris, and many more were reported by locals. Unfortunately, the snakes had disappeared once I arrived at those reported locations. Because it was raining heavily every day (in the late afternoon) during this trip in April 2006, the snakes changed positions frequently. Farmers told me that they may stay at the same place for many weeks.

So why is T. wagleri so abundant here? Well, for sure it is the high humidity found in this place, the close vicinity of the natural forest, and the abundance of food, probably increased by humans through agriculture.

Birds and squirrels were abundant in the trees, as well as house geckos and the Tockay (Gekko gecko), the call of which is easy to recognize.

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Do you see the snake? It shows a subadult female. Click on it to enlarge. This picture was taken in a garden behind a farmer's house.

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Locals reported that also brown-colored tree vipers can be found in cocoa plantations. They usually can be seen there only in the morning. Afterwards, they disappear (probably into the leaf litter, which forms a thick layer under cocoa trees). Based on this reports, I guess, it is Trimeresurus borneensis, but this has to be confirmed. Additionally, I observed a huge specimen of Trimeresurus hageni (now Parias hageni).

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Above: Three adult females from the 'valley of temple pit vipers'. All animals were photographed under daylight conditions.

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All adult females that I saw were gravid, at a time (February-April) that is consistent with observations in Thailand or western Malaysia. The juvenile male seen below was captured mid of April, thus, it was probaly born recently.

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Juvenile male, about 20 cm long. Note the basically blue coloration of the scales.

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Adult, entirely green male. This snake was collected from a sugar palm tree, several meters above the ground.

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Two vipers (adult male and subadult female), which were observed in the trees high above the ground, were in an ambush position with the head and forebody pointing upwards (see image below). This was probably because they were waiting for birds or squirrels to pass by. In contrast, on occasions when I saw these vipers on plants a few centimeter above the forest floor, they usually rested their body on a twig or leaf with the tail upwards and the head pointing downwards (see male viper in Sarawak section). Of course, this all makes perfectly sense, yet, I had not seen the ambush position in trees so clearly before. It also appeared to me that they preferred broad-leafed trees, but this based on very few observations.

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Subadult female, in transition to adulthood, resting in a tree about four meters above the ground, waiting in ambush for prey.

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It is the combination of smallholder agriculture in relative harmony with nature that makes this place special. The forests in this valley are protected, but this only because they are part of a watershed area that provides water so vital for the constantly growing city of Medan.

It is also encouraging that local farmers try to adopt environmentally friendly ways of agriculture by practising organic farming for instance (it was my professional interest in biocontrol that brought me here in the first place). In view of that, I hope that they will succeed to preserve this beautiful spot, of course, including all the hundreds or thousands of Wagleris and other wildlife living here.

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