A Note on the Chance Preying by a Western Tarsier on Fruit Bats in Malaysian Borneo
 
 
 
M.T. ABDULLAH 
Department of Zoology 
The University of Queensland 
St Lucia, Qld 4072, Australia 
email: tabdullah@zoology.uq.edu.au 
Photo from dave@hedweb.com
INTRODUCTION

Tarsiidae (Order Primates) is a distinctive family confined only to the Sunda islands, Philippines and Sulawesi. It is considered as the sister-group of monkeys, apes and man (Corbet and Hill 1992). The genus Tarsius is represented by five species, namely, Tarsius bancanus (western tarsier) which is restricted to Borneo, T. syrichta from the southern islands of the Philippines; and three species from Sulawesi, Indonesia, T. dianae, T. spectrum and T. pumilus (Corbet  and Hill 1992; Musser and Dagosto 1987). Unlike other members of the monkey and ape families, T. bancanus and Nycticebus caucang are the only representative of primates that are strictly nocturnal in habits in Borneo (Payne et al., 1985).

The subspecies in Borneo, T.b. borneanus are known from lowland areas in Sabah, Brunei, Sarawak and West Kalimantan, and above 900 m in the Kelabit highlands in northern Sarawak (Payne et al., 1985). The animal lives in the primary and secondary habitats, forages for food singly, making frequent high-pitched calls. It is active from the ground level up to 7 m in the trees, usually leaping between vertical pole to lower levels. In the wild, the diet of  the insectivorous T. bancanus is mainly large insects (Hill and Smith 1984, Payne et al., 1985). In a captive experiment, Roberts and Kohn (1993) reported of the tarsier successfully employing the sit-and-wait predatory strategy to capture live crickets. In semi-natural condition in Semengok Forest Reserve, Sarawak, Niemitz (1979) observed that  T. bancanus were feeding on beetles, cockroaches, grasshoppers, butterflies, cicadas, small nectarine birds, Kingfishers, warblers, snake and some bats. T. spectrum perched on the peristome margin and feed off the trapped insects in Nepenthes plant (Adam and Wilcock 1996).

Bats (Order Chiroptera) are also known to fall victim to a wide variety of predators such as large spiders, snakes, large lizard, birds of prey (Falconiformes and Strigiformes), mammals and some carnivorous bats (Hill and Smith 1984, Mickleburgh et. al., 1992). In Malaysia, Megaderma spasma and M. lyra prey on small vertebrate including bats (Medway 1978, Payne., et. al. 1985). The cave racer (Elaphe taeniura) and barn owl (Tyto alba) are among predators on bats (Bullock 1963). McClure et. al., (1967) observed that the main diet of cave racer snakes were mainly bats which were caught as they clung to the roof or walls in Batu Cave, Selangor. In Florida, Taylor and Lehman (1997) reported a case of predation by squirrel monkeys (Saimiri sciureus) on a solitary-roosting evening bat (Nycticeius sp). The Central American squirrel monkeys (Saimiri oerstedi) searched bat tents and successful preyed on juvenile phyllostomid bats (Boinski and Timm 1985).  On the island of Guam, introduced aboreal brown tree snake (Boiga irregularis) attacks juvenile fruit bats (Mickleburgh et. al., 1992).

There is little information on the aggressive and feeding behaviour of the free ranging western tarsiers in Borneo. This note presents the first known incident in Malaysian Borneo of a western tarsier preying by chance on two species of fruit bats mist netted in a primary lowland mixed dipterocarp forest.

 METHOD & RESULTS

Between 23 to 27 October 1996, ten to twelve Japanese-made mesh size 36 mm  mist nets measuring 12 m x 2 m were deployed at the Kubah National Park, Sarawak, Malaysia. The nets were regularly watched over from dusk (1730 hours local time) for about five hours during the night and subsequently left opened until dawn (0600 hours). Animals netted after the last check would be collected and examined early in the next morning. Netted animals were individually marked with prefixes B and MTA for release and as voucher specimens respectively. The netting site was located at 01o 36’ 26” North and 110o 11’ 21” East, 270 m above sea level. The habitat types of Kubah park is summarised in Abdullah (1999). Specimens collected were deposited at the Universiti Malaysia Sarawak museum and Sarawak Forest Department.

On the 23 October 1996, it was raining between 1600 to 1830 hours. Five bats comprising a species of insect bat and two species of fruit bats were caught in shelves 3 and 4 of net No.3 that was located within a primary forest and near the fringe of Kubah park. The mist net was deployed diagonally across the Sungai Cina to Sungai Rayu walking trail. The netting area was covered with dense undergrowth comprising of seedlings, small saplings, pole-sized and large trees. The canopy cover was estimated to be about 85%.  Three fruit bats (Cynopterus brachyotis and Balionycteris maculata) that was collected in the morning were all alive.

During the following night on 24 October 1996, the sky was initially cloudy and later became bright in the late first quarter moon phase (12th night after new moon). The last captures of two fruit bats in shelve 3 and 4 of net No.3 during that night was at 2230 hours. In the next early morning,  four fruit bats and a male tarsier (banded as B0610) were captured at various levels in a mist net No.3. The net shelves 3 and 4 (top) were found rolled up together. After unfolding the entangled animals, the  tarsier was in the third shelf (about 3 m from the ground level) with a C. brachyotis. B.  maculata  were found in the top shelf (about 4 m from the ground level) directly above the tarsier.

A lactating female C. brachyotis (MTA96314) that was entangled with the tarsier was found dead. The short-nosed fruit bat had severe and deep wounds on the forehead and left eye, and chewed left tibia, left elbow and left shoulder.  B. maculata with a female suckling juvenile were found caught in the top shelf but entangled together with the tarsier in the third shelf of the mist net. Upon closer examination it was found that both the B. maculata dam (MTA96316) and juvenile (MTA96315) were dead. The left eye of the adult bat was protruded and the facial area was severed. The left forearm of the juvenile bat was broken and apparently being chewed. It cannot be verified if the tarsier had ingested some of the chewed body parts.

On the other hand, the tarsier was alive and very aggressively defending its preys. Although C. brachyotis can be very aggressive when caught in mist net, there was no sign that the tarsier was bitten by the fruit bat. There were some remains of a large insect, a cicada species (Homoptea: Cicadoidae), near the tarsier. There are 60 species of cicadas in Sarawak that are abundant in forested areas (Zaidi and Ruslan 1998). Other non-target animals that were usually caught during bat mist netting  includes arthropods such as beetles (Coleoptera) and moths (Lepidoptera) and on one occassion an owl (Strigiformes). However, these arthropods did not attract tarsier into the mist nets. It could not be ascertain if the owl were attempting to pick up bats there that were caught in a mist net at Tawau Hills park.

Tarsiers were also captured in mist nets for bats at Poring in Kinabalu Park and Tawau Hills National Park both in Sabah and at Sungai Rayu area of the Kubah park (Table 1). A  tarsier (B0323) was captured in a mist net and within the same shelf with a Macroglossus minimus at Tawau Hills National Park; however, both animals were far apart. Other tarsiers were collected singly in the mist nets elsewhere in Borneo. All tarsiers caught were from mist nets deployed across or diagonally across forest trails that might be on the ranging routes of the species. Other species caught in such mist nets deploymment including rare flying squirrels in some survey sites in Sarawak (Abdullah and Ahmad 1999).

T. bancanus moved at a mean height of 0.89 m and utilising vertical sapling trunks of two to four centimetres in diameter (Crompton and Andau 1986). According to Roberts and Kohn (1993), captive T. bancanus preferring vertical substrates at mid-level enclosure heights of 1.2 to 2.1 m for scanning and prey capture. In arboreal locations, successful prey captures involved leaping from 60o to 90o in a downward direction onto the prey of about 0.6 m away.

The tarsier in this case might be tempted to move higher among the saplings in Kubah mist netting site due to dense undergrowth. It can be presumed that the T. bancanus might jump from a higher elevation (> 4 m above the maximum net height) onto the short-nosed and spotted-winged fruit bats that were already netted in the middle and upper shelves. It had attempted but failed to consume the fruit bats by chewing various parts of the body. The intricate entanglement of animals in the fine but strong nylon mist net had discouraged the tarsier from eating the fruit bats. Relatively, compared to the soft-bodied arthropods, the skin of fruit bats are much harder to chew. The relatively large head sizes of adult C. brachyotis (Hd = 29.66 mm) and B. maculata (Hd = 23.65 mm)  might also be a major feeding obstruction to the tarsier.  Alternatively, the tarsier was preying on the large insect that was first caught in the net before turning its attention on fruit bats. Or else C. brachyotis that is known to make loud screaming calls when caught in mist net might lured the tarsier into the net. It was found to be impossible that the tarsier was netted first followed by the fruit bats or cicada. The sagging in the third shelf caused by the heavy-bodied tarsier (WT = 110 g) had reduced the surface area of the shelf and rendered ineffective to capture other species in the same spot.

In certain cases, bats are not the regular food items for the predatory animals. For example, young bats that have fallen to the ground of the roosting cave are opportunistically eaten by bobcats (Lynx rufus), feral cats, civets, racoons (Procyon lotor) or dogs (Hill and Smith 1984).  Niemitz (1979) did not identify the species of bats preyed by tarsiers in semi-natural condition in the Semengok forest. Western tarsiers catch tiny nectarine birds and preferably eat their head and brain (Niemitz 1979). The wounds on the head region of  the fruit bats suggest that the tarsier was attempting to eat the animals. An unharmed and alive adult male B. maculata found in shelf 2 of  net No.3 suggest that death in the injured fruit bats may not be due to long exposure but shock after the vicious attack by the western tarsier.

Some of my observations on the tarsier are consistent with certain information recorded by other researchers. Circumstantial evidence showed that the tarsier was attacking and attempted to eat certain parts of  the fruit bats that were in the mist net. This is the first known  record in Malaysian Borneo of an antagonistic behaviour of a western tarsier by chance preying on B. maculata and C. brachyotis that were caught in a mist net. A detailed study on the food habits of tarsiers could provide some knowledge on the animal species they consumed, foraging behaviour and patterns. The details of some tarsiers and fruit bats mentioned in the text are shown as  Table 1.

ACKNOWLEDGEMENTS

The field work was carried out by the author and assisted by Isa Sait, Besar Ketol, Wahap Marni, Angela, Johnny and M.A. Rahman. I thank the Universiti Malaysia Sarawak for support through Research Grant 21/94 and Study Award 1995; the National Parks and Wildlife Office of the Sarawak Forest Department and the Sabah Parks for providing the permission and facilities to work in protected areas; Sarawak Museum and the Sarawak State Planning Unit for the research permit approval No. (62)dlm.UPN/807/2.

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