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DD - Bawean Warty Pig

Bawean Warty Pig (Sus blouchi)

Status: Not Evaluated

(Regarded as Data Deficient by the IUCN/SSC Wild Pig Specialist Group)

By Mark Rademaker and Johanna Rode-Margono


Taxonomy

Sus verrucosus blouchi, Groves, 1981, Bawean island.

Sus blouchi, Groves & Grubb, 2011, Bawean island.

The taxonomic description has been based on morphological measurements from four male skulls and one female skull in the 1980’s (cf. Groves & Grubb, 2011). DNA analysis is required to clarify the exact taxonomic position in relation to Sus verrucosus.

Bawean warty pig
Fig. 1:
Adult Bawean warty pig Sus blouchi at mud wallow with female in the background.


Distribution

Sus blouchi (Fig. 1) is restricted to the 192 km2-large Bawean island in the Java Sea (Fig. 2). The island has been isolated from mainland Java following rising sea-levels approximately 10.000 years ago. Since then the species has evolved separately from the mainland Javan warty pig Sus verrucosus. During a three month camera trap study (Rademaker & Rode-Margono, unpublished data) Sus blouchi was found to be present in three of the five protected areas on Bawean (total size of the protected areas 46.6 km2). The protected areas roughly coincide with borders of natural forest cover on the island, but migration between those likely occurs via patches of community forest. Density of Sus blouchi was estimated to be 5-10 pigs/km2 leading to a total population size of between 233 and 466 individuals based on total protected area size (Rademaker & Rode-Margono, unpublished data) or 180 to 386 mature pigs when the ratio between juveniles and adults is incorporated. During this study, Sus scrofa was not found on Bawean and threats to the Sus blouchi population from potential competition and hybridization as suggested for Sus verrucosus on Java appears to be absent (Blouch, 1988; Semiadi & Meijaard, 2004; 2006).


Descriptive notes

According to findings in the camera trap study by Rademaker and Rode-Margono (unpublished) adult females are estimated to measure about 50 cm shoulder height (Fig. 3).The majority of the adult males seem to attain the same height, although some videos show large males with a shoulder height of approximately 70 cm (Fig. 3). It is unclear if this is the result of intra-sex competition, in which only the top males reach maximum size, or simply due to image distortion. The 50 to 70 cm shoulder height found for adult individuals is considerably lower than the 70-90 cm shoulder height reported for Sus verrucosus (National Research Council, 1983). Other species isolated on islands have shown so-called island dwarfism, such as the red deer Cervus elaphus (Lister, 1989). Snout to tail length of two adult male pig carcasses found during the mentioned study measured approximately 110 cm. As opposed to Sus verrucosus, who have 4 carpal glands (Semiadi & Nugraha, 2009), only 3 carpal glands were present on the back of the fore-legs. Pelage coloration appears to be greyish to blackish with hues of reddish-brown present dorsally. A black mane can be present in females and juveniles (Fig. 4). There is a clearly observable band of light-golden or white hair running from the abdomen to the neck. The band typically ends in small “sideburns” and a faint band on the snout. While the beard on the cheeks (Fig. 5) is rather dark in Sus verrucosus, the beard in Sus blouchi is while and can almost reach from ear to ear via the bridge of the nose (Roland Wirth, pers. comm.). 

Fig. 2: Map of Bawean Island showing the observed camera trap rate of Sus blouchi extrapolated over each of the protected area indicating areas of high and low activity.
Fig. 3: Shoulder height of (A, above) an adult male, (B, centre) an adult female and (C, below) an immature of Sus blouchi.
Fig. 4: Sus blouchi pellage coloration observed in (A, above) adult femals and (B, below) immatures.
Fig. 5: White cheek beard of an adult male Sus blouchi reaching from ear to ear via the bridge of the nose.


Habitat, food and feeding

All behaviour and ecology information of the next paragraphs is based on the study of Rademaker & Rode-Margono (unpublished) on Bawean island conducted from November 2014 to January 2015. Sus blouchi is a habitat generalist using secondary forest, teak stands, community forest and shrubland and degraded forest. We found that the species prefers community forest over secondary forest and shrubland and degraded forest. This may be due to the presence of more energy-rich or more food in the community forest compared to the secondary forest.


Fig. 6: Nest of Sus blouchi on the forest floor.


Activity patterns

Bawean warty pigs are mainly nocturnal with peaks in the early morning and late afternoon. As is the case for Sus scrofa (Oliver, 1993), the species might be naturally crepuscular, with hunting human disturbance as the main factor leading the pigs into adopting a more nocturnal lifestyle.


Movements, home range and social organization

Based on activity patterns and distribution of videos throughout the day, Sus blouchi core areas are the secondary forests in the protected areas. During the night the species moves out of the protected areas to feed in the cultivated areas, frequently leading to human-wildlife conflict. Average group size based on camera trap data is 2.18, but groups of up to 8 individuals have been observed. Adult female to male sex ratio is 2 to 1. Home range sizes and social organizations are currently unknown. However, camera traps revealed that wallows might have important social functions. Wallows were found to attract a high number of individuals, potentially from different groups, which frequently engaged into social behavior.


Breeding

Mating behavior, gestation length and the number of offspring are unknown. Females construct nests from branches (Fig. 6).


Status and conservation

Based on the current IUCN Red List Categories and Criteria (version 3.1) the lower population estimate of 180 mature pigs means that Sus blouchi meets the threshold of less than 250 mature animals to qualify for the EN category (Criteria D). Additionally, the species’ area of occurrence is less than 100 km2. However, to be Red-Listed as CR, further criteria have to be met. This can be either a decline or severe fluctuations in the number of mature animals or in the size or quality of the habitat. So far, none of these criteria can be confirmed for Sus blouchi due to a lack of research and monitoring. Just as Sus verrucosus, Bawean warty pigs are unprotected by national law in Indonesia. A Red List Assessment could therefore help to get the species on the national agenda and start appropriate conservation measures.


Bibliography

  • Blouch, R. A. (1988). Ecology and conservation of the Javan warty pig Sus verrucosus Müller, 1840. Biological conservation, 43(4), 295-307.

  • Lister, A. M. (1989). Rapid dwarfing of red deer on Jersey in the last interglacial.

  • National Research Council 1983. Little-known Asian animals with a promising economic future. National Academic Press, Washington, D.C.

  • Oliver, W. L. R. (1993). Status survey and conservation action plan. Pigs, peccaries and hippos. Gland, Switzerland: IUCN.

  • Semiadi, G. & Nugraha, R. T. P. (2009). Some notes on biological aspects of captive Javan warty pig (Sus verrucosus). Biodiversitas, 10(3), 124-128.

  • Semiadi, G. & Meijaard, E. (2004). Survey of the Javan warty pig (Sus verrucosus) on Java and Bawean island, with English summary and detailed survey results in Indonesian. Bogor, Indonesia: Pusat Penelitian Biologi-LIPI and IUCN/SSC Pigs, Peccaries and Hippos Specialist Group.

  • Semiadi, G. & Meijaard, E. (2006). Declining populations of the Javan warty pig Sus verrucosus. Oryx, 40(1), 50-56.

  • Groves, C. & and Grubb P. (2011). Ungulate taxonomy. Baltimore, Maryland: John Hopkins University Press.