Field Notes on Pigmy Squirrels

Botany survey with Singapore Botanic Garden and Royal Botanic Garden Edinburgh at Ng Bloh RS (LEWS) on 20th February until 8th March 2017.

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Bornean Pigmy Squirrel (Exilixciurus exilis), Sabah, Malaysia. Photo credit to Ch’ien C. Lee.

Bornean Pigmy Squirrel (Exilisciurus exilis) is the second smallest squirrel after it is lost to Emily’s Pigmy Flying Squirrel (Petaurillus emiliae) for the title of the world’s smallest squirrel. As far as i have been working in the forest of Sarawak and Sabah, E. exilis is the most common forest squirrels I’ve seen. Even though they are small but the squeaking sounds of its call is very loud especially during the mid-afternoon when birds and insects are silent.

The recent trip is my second trip to Ng Bloh Research Station (NBRS) and the presence of this pigmy squirrel always attract me. In front of the hostel building, there is a few tall trees and observation can be done easily from the front porch where table and chairs is set up. I have decided to observed these pigmy squirrels closely during this trip.

On 3rd March 2017, around 1630hrs, i heard the squeaking sound came from the trees in front of the hostel building. Quickly i grabbed my binocular and start to observed this little creatures. Unfortunately, I don’t have any appropriate camera to capture a close-up photo so i use Ch’ien Lee’s photo to share here so you can see how cute and small they are.

To my surprise, there is another species of pigmy squirrel on these trees. I am only familiar with E. exilis, so i know this one is different because it have a white stripe from under of its ear and eye until above of its nose. There is also a black spot behind the ears. I get excited and keep my eye on it but i don’t know what is this species. Only when i refer to my Phillipps’ Field Guide to the Mammals of Borneo and Their Ecology (Sabah, Sarawak, Brunei and Kalimantan), i get to know this is the Black-eared Pigmy Squirrel (Nannosciurus melanotis). This species is locally common squirrel of lowland and hill forests found in most of Sarawak and Kalimantan, but absent from Sabah apart from a single provisional record from the Maliau Basin Conservation Area.

I continue my observation and it became more interesting for me to see the N. melanotis can coexist with E. exilis where both species foraging on the same trees. Even though both were feeding on the same tree but they are very particular on their feeding areas. When E. exilis was feeding on the lower part of the tree, the N. melanotis is on the top part. They didn’t bump into each other as if they were aware that they sharing the same feeding trees and even not fight to dominate the tree.

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Black-eared Pigmy Squirrel (Nannosciurus melanotis), East Kalimantan. Photo credit to Carmelo Lopez Abad.

After a while, the E. exilis jumped on the other tree and only then i can see the N. melanotis moved from top of the tree to the lower part. Now the N. melanotis moved freely on this tree and it moved faster than when the E. exilis is still there. Both of the species aware of my existence but they didn’t run away, only at the beginning they hide on the other side of the tree. It was about 30 minutes i observed them. I stopped when both of them left the tree and jump on the tree further from where i stand.

As a conclusion, it was an interesting observation because i never really observed N. melanotis as close as this time. Even though E. melanotis is not endemic and it have a wider distribution range (Borneo, Sumatra and Java) compare to E. exilis which is endemic to Borneo island. When i am getting back into the forest, i hope i will be able to encounter one more species of pigmy squirrel which is also endemic to Borneo, the Whitehead’s Pigmy Squirrel (Exilisciurus whiteheadi).

Interesting Facts Phillipps, Q. & Phillipps, K. (2016)

Many small Bornean squirrels eat small flakes of bark as a major part of their diet. Only surface bark is eaten, not the sweet inner cambium favoured by Orangutans, deer and porcupines. Bark-eating squirrels include the 3 pigmy squirrels, plus Low’s, Slender and Brooke’s Squirrels. Large areas of surface bark are removed without damage to the tree. Whitten (1987) analyzed bark eaten by Low’s Squirrel in Sumatra, but found no significant food value and very high levels of tannins. Seventeen out of 41 tree families present in the area were selected for bark eating, with Euphorbiaceae and Fabaceae being most popular.

Surface barks are made up of three indigestible substances, cellulose, lignin and suberin, a waterproofing wax. Bark is also protected by bitter antibacterial tannins. Bark-eating squirrels often eat insects, but rarely fruit. 

Possible explanation Bark-eating squirrels maybe able to digest the waxy suberin. Perhaps some Bornean trees provide edible bark to encourage small squirrels to defend the trunk against wood-eating termites and wood-boring, longicorn beetles. 

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