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The Enigma Surrounding Tigersin Tapan Valley, West Sumatra
by Matthew Linkie* and Jeremy Holden**
During a mast fruiting event in an area of low-land rain forest bordering Kerinci SeblatNational (Search) Park (KSNP), Sumatra, photo-trap-ping provided an insight into an enigmatic situationwhere 10 tigers were recorded in an area of 64 km2.These tigers may be supported by an increase ofbearded pigs, but local villagers claim they enter into this area for an entirely different reason: to eat the durian (Durio spp.), a large fruit, famous for its unpleasant smell but popular taste.
KSNP has been designated of the highest priority for tigerconservation because it still contains sufficient habitat that sup-ports a viable tiger population (Wikramanayake et al., 1998). In 1996, Fauna & Flora International (FFI) conducted a photo trap-ping survey to determine more accurate estimates of tiger numbers for KSNP as part of a wider biological diversity survey(Holden 1997). One of the locations on which the study focusedthat produced particularly interesting findings was Tapan Valley.
Tapan Valley (2.13S, 101.12E) is an area of lowland rainforest (125-400m asl) bordering KSNP. An asphalt road running through the valley bisects the park. Before this study, the valley had not been surveyed for tigers, although frequent tiger sightings and reports of secondary signs (pugmarks, scrapes and faeces) by local villagers had stimulated an interest in this area as good tiger habitat.
In November 1996, photo trapping took place over a 23-week period with 9-15 operative traps. The total effort was 31,000 trap-ping hours, from which 10 individual tigers were recorded, composing seven adults (three males, four females) and three cubsof indeterminate sex (from two females). During trapping, the number of new individuals caught increased in a linear fashionwith cumulative effort, until after about 10,000 hours of trapping, when it reached a plateau suggesting that all individualshad been recorded. If so, then this would translate into an adultdensity of 0.11 tigers/1km2for the 64 km2sampling area. Thisdensity, accentuated in part by the small sampling area, is highand would require an abundant prey base to support it, which a lowland rain forest habitat would not be able to support under normal circumstances (Eisenberg, 1980). However, photo-trapping was conducted during a durian and jackfruit (Artocarpusspp.) mast fruiting period.
The larger prey species, such as sambar (Cervus unicolor),wild boar (Sus scrofa), and muntjac (Muntiacus muntjac), wereencountered at low levels in Tapan Valley. This is possibly be-cause photo-traps were set on trails for tiger, which these ungulates use less frequently. Smaller prey, such as porcupine(Thecurus sumatrae) and pig-tailed macaque (Macaca nemestrina), were recorded at high levels.The resident ungulate populations would not have been expected to increase dramatically during the mast fruiting, unlike nomadic species, such as bearded pig (Susbarbatus), which increase their populations through movement and reproduction (Curran & Leighton, 2000).Bearded pigs and piglets were recorded in Tapan Valley towards the end of the mast fruiting period (one photo-trap recordingan adult and 10 piglets). These would have provided a supplementary prey base for the inflated tiger population.
It is unlikely that all tigers were resident, given the small area and the generally low prey base recorded over the trapping duration. Territorial markings were observed, but Tapan Valley probably formed the edge of one or several tigershome range. Tigresses with cubs would have been expected to inhabit a less disturbed range in which to mate and to sire offspring. Villagers often observed tigers crossing the road, suggesting that it didnot act as a boundary. In fact, a tiger crossing the road unsaddled a passenger on the back of a travelling motorbike.
The high occurrence of tigers in such a small area might be attributed to commercial logging, through the displacement of tigers from their ranges, causing a temporary overlap and thus higher concentration. Yet, tiger were often recorded on ridge trails less than 1 km from logging roads.
Local villagers claim that tigers always move into this area during mast fruiting periods in Tapan Valley. The durian mast fruiting periods usually occur during November-December. This coincides with the Islamic calendars bulan raya (royalmonth), which is when tiger activity is reported as being much greater in the forest.
Photo-trapping was conducted during a durian flood season, a very heavy durian fruiting event, which occurs every three years. For one month every year during this period bearded pigs are also reported as entering the forest. In Tandai, another area studied in KSNP, tiger tracks were recorded closely following the routes of bearded pigs through forest. The villagers in Tapan Valley, however, attribute theunusual tiger presence directly to the durian.
In Tapan Valley, there are wild and cultivated durian. Customary law stipulates that the collector becomes the owner of wild fallen fruit. Villagers in the valley therefore wait under fruiting trees. Once the majority of wild fruits have been collected the remaining few are left and it is believed that tigers then occupy any arising va-cancies to stake their claim on the fruit because pugmarks are often encountered around these trees. Villagers also search for fallen fruit and often find signs that a tiger has already opened some of the fruit. Tiger claw marks are observed on the tough outer shell where entry to the fruit has been made and seeds, which are re-ported as not being ingested, are also found. Sun bear (Helarctos malayanus) also prize open durian with their claws, but villagers report their marks as being different.
MacKinnon?Create|Search (1997) mentions tiger affiliation towards durian, and tigers have been reported in durian orchards from Kampung Tepoh, Malaysia, although possibly because of prey occurrence. Similar reports from Ketambe research station in Gunung Leuser National Park, Sumatra, also claim that tigers enter durian orchards during these mast fruitings, but with the intention of eating the durian (GondaNisam?Create|Search pers. comm.).
Tigers, which are obligate carnivores, were not photo-trapped eating durian in Tapan Valley, but neither were sun bear that have been photo-trapped eating durian in the primary hill forests of Siporak,KSNP.
The local villagers claim of a temporary increase in tigers during the fruiting season was supported by photo-trapping results. A sudden change in tiger presence was recorded after the mast fruiting period, with only one tiger and no secondary signs being recorded in the eight weeks succeeding, where previously nine tigers were recorded and pugmarks encountered every day. In contrast, residentA sian tapir (Tapirus indicus), anotherlarge bodied mammal, were recorded at avery high density in Tapan Valley duringand after the mast fruiting period (Holdenet al., in prep).The situation in Tapan Valley is still unclear and further photo-trapping over subsequent fruiting and non-fruiting periods would be required for a fuller understanding, but commercial and illegal logging, mining and ensuing subsistencefarming activities have cleared the majority of forest surrounding previous trap locations thus ensuring that Tapan Valleyremains an enigma.
Curran, L.M. & Leighton, M. 2000 Vertebrate responses tospatiotemporal variation in seedproduction of mast-fruiting Dipterocapeae. Ecological Monographs, 70,101-128.
Eisenberg, J.F. 1980. The Density and Biomass of Tropical Mammals. In Conservation Biology: Anevolutionary ecological perspective, (eds) Soul, M.E. &Wilcox, B.A. Sinauer Associates, Massachusetts.
Holden, J. 1997. Results of photo-trapping; Kerinci Seblat NationalPark?Create|Search and adjoining areas. Fauna and Flora International unpublishedreport.
Holden, J., Yanuar, A. and Martyr, D.J. inprep. The Asian tapir in the Kerinci Seblat National Park, Sumatra:evidence collected through photo-trapping.
MacKinnon?Create|Search, K., Hatta, G., Halim, H. andMangalik, A. 1997. The Ecology of Kalimantan (Indonesian Borneo).Oxford University Press, UK.
Wikramanayake, E.D., et al. 1998 Anecology-based method of defining priorities for large mammal conservation: the tiger as a casestudy. Conservation Biology 12,865-878
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