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Conservation and population status
of the Philippine warty pig (Sus
philippensis) within the Obu Manuvu
Ancestral Domain in Davao City,
Mindanao Island, Philippines
Keywords: Camera trapping, key informant interviews, relative abundance index
Jhonnel P. Villegas
Davao Oriental State College of
Science and Technology (DOSCST)
City of Mati, Davao Oriental
Email: jhonnelvillegas@gmail.com
Jireh R. Rosales
DOSCST
The Philippine warty pig (Sus philippensis) is endemic to the Philippines, where
habitat loss, hunting, and hybridization continue to cause population decline.
To increase knowledge about the understudied Mindanao sub-species, an
assessment of its conservation and population status within the 36,000-ha Obu
Manuvu Ancestral Domain (OMAD) in Davao City was undertaken. Specically,
this study aims to determine the relative abundance of
S
. philippensis and
document the existing conservation efforts. The species was documented through
camera trapping to calculate the relative abundance index (RAI). Also, key
informant interviews with 12 Obu Manuvus were undertaken to investigate local
efforts to conserve the species. A total of 18 individuals of
S
. philippensis were
detected after 500 camera trap-days (RAI=2.0). Eight individuals were observed
in Tambobong (RAI=3.2), ten individuals in Salaysay (RAI=4.8), but none were
observed in both Tawan-tawan and Carmen (RAI=0.0). The results indicate a
low relative abundance of
S
. philippensis in the study areas. The interview results
revealed that hunting and habitat loss are the major anthropogenic threats within
the ancestral domain. Current policies and strategies for species protection and
forest management must be amended and the improved guidelines must be
strictly enforced.
Jayson C. Ibañez
Philippine Eagle Foundation
Davao City, Davao del Sur
University of the Philippines - Mindanao
Davao City, Davao del Sur
Sylvatrop, The Technical Journal of Philippine Ecosystems and Natural Resources 32 (1): 1–14
2 J. Villegas et al.
THE PHILIPPINES IS HOME TO SEVERAL SPECIES OF WILD PIGS:
Sus ahoenobarbus
Huet, 1888 in Palawan; Sus cebifrons Heude, 1888 in Negros, Cebu,
and Panay; Sus oliveri Groves, 1997 in Mindoro; and Sus philippensis Nehring, 1886
in Luzon, Mindanao, Basilan, Leyte, Samar, Catanduanes, and Mindoro (Groves 1997;
Heaney et al. 2016). Most of the species are endemic to the Philippines, making the
country home to the largest number of endemic wild pigs in Southeast Asia next to
Indonesia (Oliver 1995).
Sus philippensis, also known as Philippine warty pig, is characterized by grey
skin with black or dark brown hair. They have long hair on the head, extending to the
back of the neck and shoulders. Adult males have conspicuous tusks and warts on the
face and white hair on the side of the jaw (Groves 1997; DENR-BMB 2020).
The current population of S. philippensis is believed to be declining because
of hunting and habitat loss. On the island of Marinduque, S. philippensis is now
considered extinct (Monleon et al. 2010). The hybridization of wild pigs with
domestic species also contributes to further declines (Heaney and Meijaard 2017). The
Philippine Red List Committee (PRLC) and the International Union for Conservation
of Nature (IUCN) have categorized the species as "Vulnerable", under threat from
various factors (Heaney and Meijaard 2017; DENR-BMB 2020).
On Mindanao Island, S. philippensis is also thought to be widely distributed.
However, scientic assessments that provide precise information on its population's
status are still lacking (Heaney and Meijaard 2017). Like in many parts of the country,
wildlife law enforcement remains low despite the national law protecting threatened
wildlife, such as Republic Act No. 9147, or the Wildlife Resources Conservation
and Protection Act. This study intends to address the knowledge gap by providing
the rst scientic assessment of the relative abundance and conservation status of
S. philippensis inside the Obu Manuvu Ancestral Domain (OMAD) in Davao City,
Mindanao Island, Philippines.
Materials and methods
Study area
Four barangays, namely, Carmen, Tambobong, Tawan-tawan, and Salaysay in
Baguio District, Davao City, Davao del Sur, were surveyed using camera traps to
assess the presence and population of S. philippensis (Fig. 1). The Obu Manuvu tribe
traditionally occupies these land areas, covering 36,712.52 ha as part of the OMAD.
Selected regions of the ancestral domain are also recognized as a watershed and
declared an Indigenous and Community Conserved Area (ICCA).
3
Conservation and population status of Sus philippensis
Figure 1 Location of the study area and sampling sites in the Obu Manuvu
Ancestral Domain in Davao City, Mindanao Island, Philippines
Camera trapping
Camera trapping is a useful tool in Philippine wildlife research and conservation.
It is widely used to monitor the Philippine pangolin’s (Manis culionensis) population
status and distribution (Ingram et al. 2019; Willcox et al. 2019). Habitat monitoring
among deer species (Rusa spp.) also employs camera trapping methods, thereby
informing conservation decisions (Ali et al. 2020). As an alternative to direct
observation methods, the use of camera traps is non-invasive, less laborious, and
yields rich data (Kays et al. 2011). However, its usage is relatively uncommon in the
country due to high cost, in situ theft, and unpredictable performance in extreme
environmental conditions.
In this study, ten camera units—four HCO Scoutguard SG560C and six Bushnell
Trophy Cam HD Aggressor No-Glow Trail camera traps—were used. The HCO
Scoutguard SG560C has a highly sensitive passive infrared (PIR) motion sensor, a
visible ash, high-quality photos up to 8 megapixels, and a maximum detection
range of 25 m. On the other hand, the Bushnell Trophy Cam HD Aggressor No-
Glow Trail camera trap also has a high PIR motion sensor, 48-LED No-Glowash,
high-resolution stills, or HD video up to 20 MP resolution, and a 0.2-s trigger speed.
All cameras were set to capture three consecutive photos and 30-s videos.
4 J. Villegas et al.
A 2.5-km transect was established within each of the four barangays. In each
transect, 10 camera trap stations were installed. The camera traps were mounted on
sturdy trees at a maximum height of 1.5 m from the ground and a minimum distance
interval of 250 m, depending on the evidence of S. philippensis's presence (Kays et al.
2011). Animal trails, feces, or other signs of the mammal's presence were considered
for each camera trap's installment. Furthermore, the weather during the sampling
period, microhabitat around the camera trap stations, and encountered threats and
disturbances were documented. Once mounted, the 10 camera traps were left in
the wild with constant monitoring for 12.5 d, for a total of 125 camera trap-days per
barangay. Overall, 500 trap-days were completed in four barangays. Data gathering
was conducted from January to March 2020.
Several factors were considered to minimize the repetitive counts of
S. philippensis individuals. Visible marks were identied to differentiate individuals,
such as white hairs on both sides of the jaw for the male adult individuals. For the
females, their size and general morphology were recorded to differentiate individuals.
The differences in the morphology and the date and time that the individuals were
photographed were noted. Also, a 30-min independence interval was observed. Lastly,
as local experts for identifying this species, the forest guards also helped differentiate
the individual species photographed by the camera traps.
Key informant interviews
One by one, twelve Obu Manuvu forest guards, elders, and leaders participated
in the key informant interviews (KIIs) undertaken in this study. The participants were
selected based on their familiarity with the investigated landscape and long-term
association with the natural environment. They were asked about their perceptions
of the population and conservation status of S. philippensis. In-depth discussions on
the conservation threats observed and strategies implemented by the Obu Manuvu
indigenous community were also conducted using a prepared interview guide. The
interview guide was validated by experts before being utilized in the research process.
All interview sessions were recorded, transcribed, and analyzed through qualitative
techniques.
Relative abundance index
The relative abundance index (RAI) presents a descriptive and crude measurement
of species abundance. It can be affected by various factors, such as the location of
camera traps, weather, etc. However, in this study, the primary goal is to estimate the
S. philippensis population status. RAIs are less complicated and often used for species
that are difcult or costly to monitor (Palmer et al. 2018). The total detection counts
in every barangay were tallied and divided by 125 trap-days. The overall RAI was
5
Conservation and population status of Sus philippensis
computed by dividing the total detection counts in all barangays by 500 trap-days
using the formula of Jenks et al. (2011) indicated below:
Results and discussion
Abundance and distribution
An estimated 18 S. philippensis individuals were photographed in all barangays
within the OMAD. Eight individuals were observed in Tambobong, ten individuals
in Salaysay, and none were observed in Tawan-tawan and Carmen (Table 1). This
result indicates a low relative abundance for S. philippensis in the ancestral domain,
supporting the Vulnerable status under the Philippine Red List of Threatened Wild
Fauna (DENR -BMB 2020).
Table 1 The relative abundance index (RAI) of the Philippine warty pig (Sus
philippensis) in the Obu Manuvu Ancestral Domain
Barangay Independent
detection
Detected group sizes of
independent events Trap days RAI
Tambobong 2 (station 4) 1;1 125 3.2
2 (station 10) 1;5
Salaysay 1 (station 13) 1 125 4.8
1 (station 14) 1
2 (station 15) 6;1
2 (station 20) 1;1
Tawan-tawan 0 — 125 0
Carmen 0 — 125 0
Total 10 500 2.0*
*average
The cameras were installed in the forest of Tambobong from January 7 to 19,
2020. Only stations 4 and 10 captured wild pigs in photos and videos (Fig. 2). Station
4 is located at 1,048 masl, with coordinates of 7°10'25.19"N and 125°15'52.25"E.
An adult individual was detected on January 15, grazing around the area, and a
young individual was also observed on January 17 at this station. On the other
6 J. Villegas et al.
From 22 January to 3 February 2020, the cameras installed in Salaysay stations
13, 14, 15, and 20 were able to capture S. philippensis's photos and videos. Station
13 is located at 1,550 masl, with coordinates of 7°11'29.88"N and 125°14'0.27"E,
where an adult was observed roaming the area on January 25. Station 14 is located
at 1,540 masl, with coordinates of 7°11'26.51"N and 125°13'57.97"E, where the
hairy back of an adult individual was documented on January 31. Station 15 is located
at 1,533 masl, with coordinates of 7°11'16.56"N and 125°13'57.97"E. In the rst
recorded video, a sounder of six individuals, suspected to be a family, were observed
passing. In another video, an individual is also passing by, recorded on January 27
(10:29 AM and 10:42 AM). Lastly, station 20 is located at 1,516 masl with coordinates
of 7°11'33.70"N and 125°14'12.20"E. One individual roaming the area was also
observed on January 30.
Tambobong has a broad forest cover but shows a lower RAI (3.2) for
S. philippensis than Salaysay (4.8) (Table 1). This low RAI is influenced by the location
where the camera traps were installed. As shown in Figure 1, the camera traps were
hand, station 10 is located at 1,367 masl with coordinates of 7°10'46.39"N and
125°15'52.54"E, where an individual was observed on January 11 and a sounder
of ve on January 12.
Figure 2 Documented Sus philippensis at Station 10 in Tambobong,
Davao City, Mindanao Island, Philippines
7
Conservation and population status of Sus philippensis
placed near the non-forested areas where human settlement is evident. Human trails
and logging roads were also observed. S. philippensis is known to be sensitive to
human disturbances. Several studies provide evidence that they tend to be active in
areas with fewer anthropogenic disturbances (Podgorski et al. 2013; Johann et al.
2020). Nevertheless, S. philippensis was still documented in this area. This indicates
that this species is tolerant to slight disturbances and is mostly active at night (Johann
et al. 2020).
Another area surveyed is Salaysay, where ten individuals were captured, resulting
in a higher abundance (RAI=4.8) than the other barangays. As shown in Figure 1, the
camera traps were installed in the forest’s innermost area, less likely to be visited by
the tribe members, as no human trails were observed. Moreover, the site is denser in
vegetation, with swampy areas and river tributaries, a favored habitat for the species
(Graves 1984; Allwin et al. 2016). Thus, S. philippensis is expected to be more
abundant here compared to other sampling areas.
On the other side of OMAD, Carmen and Tawan-tawan have relatively the
same forest cover. During the transect walk, signs of S. philippensis, such as fecal
pellets, hoof prints, and browsing areas, were observed. However, no individuals
were photographed, resulting in zero RAI. S. philippensis tends to roam and move
from one forest patch to another. According to the local interviews, most of the
forest cover in these barangays is already denuded. Food availability, population
density, reproductive activity, quality and interspersion of habitat, season, and human
disturbance are among the factors that cause the wandering or drifting movement
behavior of S. philippensis. Though they are known to wander in a dened area
or home range, intensive and prolonged disturbances can permanently trigger these
species, like Sus scrofa, to move to more remote locations for foraging and comfort
behavior (Allwin et al. 2016; Erdtmann & Keuling 2020). There is a possibility that
during the sampling period, S. philippensis was present in other areas of the forest not
covered in this study.
Several studies on the habitat of S. philippensis claimed that this species is
now common in remote forests only. It was reported in the montane and mossy
forests with an elevation of 925–2,150 m by Heaney et al. (2005) in their study at the
Balbalasang National Park, Kalinga Province. This information is consistent with this
study’s result that the species were observed at elevations above 1,000 m. Likewise,
with S. ahoenobarbus in Cleopatra’s Needle, Palawan, high elevation habitats could
be a consequence of severe hunting pressure (Marler et al. 2015).
This study’s ndings conform with the ‘Vulnerable’ status of S. philippensis
as published by the Philippine Red List Committee (PRLC) and the IUCN Red List
of Threatened Species (Heaney and Meijaard 2017; DENR-BMB 2000). Only 18
8 J. Villegas et al.
S. philippensis individuals were detected in the surveyed sites within 500 camera trap
days. The RAI value is equivalent to 2.0, implying a low population density.
Aside from S. philippensis, the camera traps also detected other species such
as Philippine brown deer (Rusa marianna), common palm civet (Paradoxurus
philippensis), long-tailed macaque (Macaca fascicularis), Mindanao treeshrew
(Urogale everetti), Philippine pygmy squirrel (Exilisciurus concinnus), and other
unidentied rodent species. There is a need to standardize camera trapping in wildlife
studies to maximize the potential of its application in research and conservation,
especially for less-studied species such as S. philippensis.
Habitat and environmental factors
The sampling period for all the study sites occurred during the dry season of the
year, although occasional rains were also recorded. In an interview with the hunters,
hunting S. philippensis is seasonal, occurring at its highest frequency during drier
months. This season corresponds with heavy fruiting, hence the increased foraging
activities (Scheffers et al. 2012). It can be inferred that S. philippensis is mostly active
during the drier season. This study detected the species during drier days, both during
the daytime and at night.
The camera traps were installed in locations with S. philippensis hoofprints and
muddy browsing areas within a dipterocarp forest. Dominant tree species include the
Philippine oak tree (Quercus subsericea), locally known as “Ulayan”, and fern trees
(Cyathea spp.) with leaf litter ranging from 1 to 4-cm thick. Moreover, the species’
suspected nesting sites and microhabitat were also considered in determining the
camera trap stations. A pig's nest was observed in an area with dense vegetation,
several meters away from the nearest water source, at 1,510 masl in Salaysay and
1,540 masl in Tawan-tawan. Twigs, grasses, and other plant debris stacked in a circular
position characterize the S. philippensis’ farrowing nests (Fig. 3). This description
corresponds to the ndings of Fernandez-Llario (2004).
Furthermore, the elevations where farrowing nests were observed agree with
Heaney et al.’s (2006) result at 1,000–1,475 masl. Even though signs of S. philippensis
presence (i.e., hoofprints, fecal pellets, browsing areas, and den) were documented
across the sampling stations, not all camera traps were able to record their activities.
9
Conservation and population status of Sus philippensis
Figure 3 Farrowing nest of the Philippine warty pig (Sus philippensis) in
Barangay Salaysay, Davao City at 1,510 masl
Conservation threats and efforts
Based on the interviews, the tribe refrains from hunting wildlife species in
the forest because of their beliefs. The Obu Manuvu tribe considers the forest as
Pusaka, a tradition of sanctifying living or non-living objects that possess historical
value, relevance to faith, cultural signicance, economic benets, and value to the
ancestral domain. Wildlife species such as S. philippensis are considered valuable
and identied as Cultural Keystone Species (CKS), noting their critical contributions
and function to the indigenous community's socio-cultural structure (Donato 2011;
The Unied Obu Manuvu Tribal Council 2017).
With this belief, hunting any wildlife species in most parts of the forest is highly
prohibited. Only traditional hunting at certain places is allowed, provided that a ritual
must be performed before hunting. However, there are reports that outsiders, who
are unaware of this belief, sometimes hunt wildlife species such as S. philippensis.
Hunting is usually done using a gun, a lit-ag (a trap to catch wildlife), or by pangayam
(hunting with dogs). The meat is either consumed locally or sold in the markets, like
in the Luzon Islands (Heaney et al. 2016). It has become a recurrent problem that
Obu Manuvus addresses through a community-based conservation approach.
10 J. Villegas et al.
Aside from hunting activities, habitat destruction is among the many factors that
cause the species' decline (Cox 1987; Oliver 1995). Agricultural plantations, such as
cacao, banana, and vegetables, are found at an elevation of 1,000 masl and above.
Moreover, slashed trees, mostly young trees, were also observed in some areas of the
forest. Other trees were also seen with peeled bark, a traditional way of dehydrating
trees before they are cut down for logs. These, among other practices, contribute to the
signicant destruction of the S. philippensis habitat.
In some barangays, like in Carmen, locals use proper land zoning and boundary
markings in which there are only certain areas where agricultural activities are
allowed (Donato 2011). Some areas were declared to be culturally conserved areas,
where activities such as wildlife hunting and illegal logging are strictly prohibited.
Other indigenous conservation practices of the Obu Manuvu community
were also documented. As mentioned, the tribe sancties items, animals, and
lands that are considered valuable to their lives and history, locally called Pusaka.
They have organized a tribal council named the "Pusaka Council", which enforces
policies and imposes restrictions in the ancestral domain. One of their strategies
is the organization of a team of local forest guards trained to monitor wildlife and
conduct regular patrols within their forests. Fortunately, they are also supported by
non-government organizations (NGOs), such as the Philippine Eagle Foundation
(PEF) and the Davao City Government. The local communities formulated their
conservation policies anchored on the Pusaka. The systems include prohibiting the
cutting of trees near bodies of water. Tree cutting must rst be approved by the tribal
council and supervised by the forest guards, and then followed by a tree planting
activity. Violators are punished through customary and existing government laws.
The Pusaka Council's customary laws include "pomaas", a conventional ne that
consists of 50 kg of meat, rice, and PHP 1,500.00. In addition, those who cut trees
must plant 100 trees in suitable areas (Donato 2011; The Unied Obu Manuvu
Tribal Council 2017).
These strategies and policies set by the Obu Manuvu tribe are useful tools for
conserving and protecting wildlife. As Ibanez and Carig (2013) mentioned, the
indigenous community has their natural ways of knowing how to conserve species
and habitats, which should be harnessed. Private and government sectors should
recognize indigenous knowledge, skills, and labor by providing incentives, which are
now applied in the Obu Manuvu Indigenous community.
With consistent conservation efforts, the tribe perceives that S. philippensis
population is gradually recovering. However, recent assessments show that
S. philippensis populations are now heavily fragmented and rapidly declining across
the country (Heaney and Meijaard 2017; DENR-BMB 2000). The declaration of a
11
Conservation and population status of Sus philippensis
total hunting ban within the ancestral domain may allow the species to recover fully.
There is a need to adopt more proactive forest restoration initiatives, such as planting
native trees. The threats from emerging diseases must also be considered, especially
the rapid spread of African Swine Fever (ASF) in Southeast Asia, which is threatening
the endemic S. philippensis (Luskin et al. 2020).
Conclusion
The estimated number of S. philippensis in the Obu Manuvu tribe's Ancestral
Domain indicates a low relative abundance. Several anthropogenic threats such as
hunting and deforestation were observed despite the Obu Manuvu community's local
conservation efforts. The zero results in Carmen and Tawan-tawan denote that the
S. philippensis is low, implying that current strategies and policies for forest management
must be strengthened and enforced. There is a need to enhance the forest monitoring
scheme by providing more support to the local forest guards. Regular monitoring of
large mammals must be conducted annually. Also, prevention measures against the
ASF and other diseases must be integrated to prevent the quick decimation of the
S. philippensis population. While only a portion of the ancestral domain has been
studied, it is recommended to conduct more assessments in other areas not covered in
this study. It is essential to investigate the S. philippensis in different seasons further to
determine their temporal distribution and movement patterns. More extended sampling
periods and installing more camera traps would be better to obtain more data. Lastly,
studies on species behavior, habitat use, distribution, and movement patterns must be
conducted using advanced technologies such as radio telemetry.
Acknowledgment
This study is made possible by the support of the American people through the
United States Agency for International Development (USAID). The contents of this
study are the sole responsibility of the authors and do not necessarily reect the
views of USAID or the United States government. The team would also like to thank
DOSCST, especially Dr. Edito B. Sumile, State Universities and Colleges President
III; Dr. Roy G. Ponce, Vice President for Research, Development, and Extension;
Dr. Misael B. Clapano, Director for Research, and the Gender and Development
Center team; the USAID Protect Wildlife with Ms. Maria Rona Villanueva and
Ms. Resanee Peteros; the Philippine Eagle Foundation (PEF) with Ms. Mary Grace
Abundo, Mr. Guiller Opiso, and Ms. Jimbea Lucino; the Obu Manuvu Unied Tribal
Council of Leaders and Elders with Mahabbok Luis A. Lambac, and Lipatuan Joel
A. Unad; and the Forest Guards of Barangay Carmen, Salaysay, Tambobong, and
Tawan-tawan.
12 J. Villegas et al.
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