Friday 5 August 2022

Pesta Ubin 2022: Fun @ Pulau Ubin Shore to Summit Walk


Pesta Ubin 2022: Fun @ Pulau Ubin Shore to Summit Walk
By Tan Shin Ying, NSS intern

On 25 June 2022, NSS Education Committee Vice Chairperson Gloria Seow led a group of 19 NSS members on a fun shore to summit walk at Pulau Ubin. The walk coincided with Ubin Day, the finale for Pesta Ubin, an annual festival celebrating the culture and environment of Pulau Ubin.

Right after getting off the boat, Gloria directed our attention upwards to some Asian Glossy Starlings perched on the roof of the jetty. Why the bird is so named became apparent to us as the adult’s glossy green plumage shone beautifully under the sun. These birds are highly gregarious and are often found in large flocks at fruiting trees and roosting sites throughout Singapore. A good example are the ones we can hear calling raucously along Orchard Road in the evenings.

Asian Glossy Starling perched on the roof of the jetty.


Near the Assembly Area, we found ourselves gazing at what seemed to be a cluster of trees. In truth, it is a single Strangling Fig or Banyan Tree surrounding a shorter host tree. Gloria explained that a Strangling Fig begins life on the branch of its host, extending its aerial roots downwards which thicken to form pillar roots that resemble tree trunks. These roots progressively surround the host tree and prevent it from growing in girth. Overtime, this tree also tends to out-shade its host with its taller canopy. True to its name, the Strangling Fig might eventually ‘strangle’ its host tree to death.

Strangling Fig surrounding the host tree.

On our way to Pekan Quarry, we were excited to see a Golden Orb Web Spider’s giant web next to the path. Weaving the second largest web in the world, the beautiful hand-sized female spider immediately drew oohs and aahs. This native spider exhibits sexual dimorphism, with the female’s body length of 40 mm to 50 mm nearly 10 times bigger than that of the male’s 5 mm to 6 mm body length.


Female Golden Orb Web Spider.


We observed the native Dutchman's Pipe growing along the fence at Pekan Quarry. This is the host plant of Singapore’s National Butterfly, the Common Rose, whose caterpillar feeds on the climber’s toxic leaves. Gloria shared that the caterpillar and adult butterfly in turn acquire the toxins and ‘dare’ to be highly visible. This is an example of aposematic or warning colouration, where the bright colours of the insect advertise that it is toxic, so that birds and other predators avoid eating them. We were happy to see several Common Rose butterflies fly by. At Pekan Quarry, we peered through the scopes provided by Ubin Day volunteers, for close-up views of the Grey Heron colony and even a Brahminy Kite.

 Passing through the mangroves at Jelutong Bridge, we were greeted with numerous Mud Lobster mounds reaching about 1 m tall. They act as ‘condominiums’ for numerous species including Tree-Climbing Crabs, snakes, spiders and insects. Despite being common, Mud Lobsters are rarely seen as they are mostly underground recycling nutrients in the ecosystem through their feeding excavations. Gloria pointed out colourful Fiddler Crabs lining the mudflats. The male fiddler has one greatly-enlarged claw that he waves around to court females and fend off rivals, but is too big to use for feeding. With only one functional feeding claw, males are less efficient in stuffing themselves compared to female crabs with two feeding claws.

We found many Archerfishes and Striped-nosed Halfbeaks swimming in the mangrove river. The archerfish can shoot a jet of water to knock an insect off a leaf into the river below and its waiting mouth. Halfbeaks have lower jaws much longer than their upper jaws, which they use to scoop food floating on the water surface. Their diet includes algae, zooplankton, insects and small fishes.

Our final stop was climbing up Puaka Hill. At 74 m, it is the highest point on the island. Gloria directed our attention to a White-bellied Sea Eagle’s nest built on a tall tree on the other side of scenic Ubin Quarry. This is Singapore’s largest resident raptor with a 2-m wingspan. Sea-eagles are known to repair and reuse their nest each breeding season. Overtime, a nest can become too heavy and snap the branches. We admired a Weaver Ants’ nest halfway up Puaka Hill. Weaver Ants work together to pull the edges of leaves into shape to form a nest, woven together by sticky ant larvae silk.

Weaver Ants’ nest.

This walk was an eye-opening experience for me, and is suitable for participants of all ages. Many thanks to Gloria who guided the group through the walk very patiently and eloquently, allowing everyone to learn more about the flora and fauna that can be found on Pulau Ubin.

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