| Citation |
Mildenstein, T. & Paguntalan, L. 2016. Acerodon jubatus. The IUCN Red List of Threatened Species 2016: e.T139A21988328. https://dx.doi.org/10.2305/IUCN.UK.2016-2.RLTS.T139A21988328.en. Accessed on 27 April 2022. |
Description |
JUSTIFICATION
Listed as Endangered because of a population decline is suspected to be more than 50% over the last three generations (30 years; Pacifici et al. 2013). The decline is suspected from the species dependence on native forest (Mildenstein 2012) and the observed reduction in the extent of its lowland forest habitat. The species is also extremely sensitive to hunting in general, and especially to roost site disturbances. Only 3 of the 12-15 remaining populations known to contain this species are at roost sites that are essentially protected from most disturbance (Subic Bay, Boracay, Mambukal), and even these populations in the best case scenario are declining at a rate of 10-15% per generation (Mildenstein 2012). Finally, population sizes of this species are very small, most (9 of 12 known populations) containing fewer than 200 individuals, and many of those with fewer than 50 individuals. With the inferred population dynamic and genetic challenges associated with small populations, it is assumed these populations decline are exacerbated by their small sizes.
RANGE DESCRIPTION
This species is endemic to the Philippines, where it is widespread with the exception of the Palawan faunal region and among the Batanes and Babuyan island groups (Heaney et al. 1998). It generally occurs at an altitude range of 0-1,100 m asl. It is only found in large roosts with Pteropus vampyrus. Although P. vampyrus roosts have been, and are often still assumed to have A. jubatus present, the presence of A. jubatus at many roosts has not been confirmed. There are historic records for the species on the following islands: Basilan, Biliran (forgaging from a roost on Maripipi - Rickart et al. (1993)), Bohol, Bongao, Boracay, Cabo (in Igat Bay, in Zamboanga del Sur Province, off Mindanao), Cebu, Dinagat, Jolo, Leyte, Luzon, Marinduque, Maripipi, Mindanao, Mindoro, Negros, Panay (formerly regarded as Acerdon lucifer), Polillo, Sibutu and Siquijor.
Recent surveys by the Bat Count Project (source Bat Count reports: Mildenstein et al. 2005, and Mildenstein 2011, unless alternative source given) on the presence and absence of A. jubatus at various bat colonies on islands in the Philippines report its presence at the following sites: 1) Bohol Island: Raja Sikatuna Protected Landscape, Bilar, 2) Boracay Island: A roosting colony was known that feeds on nearby Panay, but has recently been reported missing (M. Saulog pers. comm. 2011), 3) Cebu: A roost at between barangay Malones and Lanao, Dalaguete: and second roost was located in Boljoon town in southern Cebu in 2008 (L. Paguntalan pers. comm. 2011), 4) Leyte: Bilaran Island (L. Paguntalan pers. comm. 2011) and a colony at Mount Pangasugan, but Acerodon jubatus presence is unconfirmed, 5) Luzon: There are confirmed roosts documented from Subic Forest Watershed Reserve, Subic Bay, Northern Sierra Madre Natural Park, Divilacan, Cagayan, and in Ilocos Norte province, Pangasinan province, Baler in Aurora province, and Calamba in Laguna province (P. Alviola pers. obs. 2005), and possible roosts on Mount Banahaw (D. Balete pers. obs. 2003) and Kamunayan-Tabugan, Baggao, Cagayan (M.R. Duya pers. comm. 2005), 6) Mindanao: Roosts are known from Mutia, Calamba and Oroquieta City, Mount Malindang, Misamis Occidental (Ramayla, pers. obs. 2006, Nuñeza et al. 2006), Mount Hamguitan, Eastern Mindanao (D. Balete pers. obs. 2005), Malagos Forest Watershed Reserve, Davao (N.R. Ingle pers. obs. 2004, Gomez in litt. 2007, and Bat Count Project), and Mt. Diwata, Agusan del Sur (Nuñeza et al. 2008). In Siocon and the Philippine Coconut Authority Area in Zamboanga del Norte, there is a roost of about 5,000 individuals of Pteropus vampyrus and Acerodon jubatus (according to trained students and the DENR), and Desmond Allen photographed a roost of Acerodon jubatus and Pteropus vampyrus in Bongao, Tawi-tawi (between 2003-2007). Possible roost sites, where the presence of the species requires confirmation, are in: Magum and Mati, Davao Oriental, Malita, Davao del Sur, and Mount Hilong-hilong, in the lowland dipterocarp forest of Cantilan and Carrascal, Surigao del Sur (Gomez in litt. 2007), 7) Mindoro: a roost occurs at Bilog na Sapa, Sablayan, Mindoro Occidental and possibly on the eastern side of the island (Saulog and Garcia pers. comm. 2005), 8) Negros: Calinawan, Enrique Villanueva and Sibulan, in Negros Oriental, Mambukal, Barangay Minoyan, Murcia, Mount Patag, and possible roosts in a mangrove area in the towns of Sagay, Hinoba-An, and Isabella near Mt. Kanlaon (L. Paguntalan pers. comm. 2011) and in the Manlukahoc area (E. Alcala pers. comm. 2006), Negros Occidental, and 9) Polillo: a roost occurs on privately owned land (Alviola pers. comm. 2006).
The Bat Count Project has surveyed the following colonies of Pteropus vampyrus and did not find any A. jubatus (though it is unclear whether the species occurred in any of these roosts historically (Mildenstein 2011)): 1) Cebu: Tabunan, 2) Mindanao: Bongo Island, Maguindanao Province, and Pinol and Maitum, Sarangani Province, 3) Negros Oriental (southeast Negros): Sagay, Vallehermosa and San Jose, and 4) Panay: Batbatan Island and Culasi, Antique Province. The Siquijor populations are possibly extinct (Lepiten 1995), this species has been reported absent from there recently (A.B. Cariño pers. comm. 2006).
DESCRIPTION
A rough estimate of the total population of A. jubatus is around 10,000 individuals (and probably no more than 20,000) (Mildenstein 2011, 2012). During the late 1800s and early 1900s there were many anecdotal reports of colonies of 100,000 bats, presumably mixed species. Hence, the total population of A. jubatus is estimated to be around one or two percent of what it was 200 years ago (L. Heaney pers. comm. 2006). Although there are still a few mixed species colonies that number between 10,000 and 30,000 individuals, generally, recent observations of mixed colonies have reported sizes of 5,000 and fewer individuals (Mildenstein 2011, 2012), and concur with surveys from the last three decades (Heaney and Heideman 1987, Heaney and Utzurrum 1991, Mudar and Allen 1986, Rickart et al. 1993, Utzurrum 1992).
Prior to fruit bat population surveys of the early 2000’s, most colonies of large fruit bats were assumed to include Acerodon jubatus, although the actual presence of the species in many colonies was not confirmed. Recent work by the Bat Count Project has shown that the number of remaining A. jubatus populations is fewer and population sizes are smaller than were thought to exist historically. Many fruit bat colonies do not have any A. jubatus at all, and when it is present, it has always been found in mixed species roosts with Pteropus vampyrus (and sometimes also with Pteropus hypomelanus). Of the 23 roosts sampled by Bat Count, only nine of these were found to contain A. jubatus during several survey days for each roost. For other roosts surveyed by Bat Count Philippines, the presence of the species was not documented, but repeat visits are necessary to confirm absence. It is not known whether colonies lacking A. jubatus represent extirpated locations or if the species was not found in these sites historically.
For most colonies known to be of mixed species, it is often unknown how abundant each species is in the colony (i.e. the species composition) (Mildenstein et al. 2005, Mildenstein 2011, 2012). In the mixed colonies that have been surveyed, A. jubatus make up a small proportion of the total colony size, ranging from A. jubatus making up around 5% of the mixed species population to as much as 20% of the individuals in the two most protected colonies (Mildenstein et al. 2005, Mildenstein 2011, 2012). In sites that are heavily disturbed, A. jubatus are often <2% of roosting population (Mildenstein 2011, 2012).
Along with being small and much less numerous, A. jubatus populations are also more isolated than Pteropus vampyrus populations. Molecular study of fecal samples from Subic Bay and Mambukal suggest there is moderate amount of population structure among A. jubatus populations (Mildenstein 2012), which would be expected given the species greater amount of forest specialization.
HABITAT AND ECOLOGY
This is amongst the heaviest of the worlds bats at up to 2.6 pounds (1.2 kg). Currently, it is always found roosting with Pteropus vampyrus (and sometimes Pteropus hypomelanus), but it is uncertain if it has always occurred in mixed roosts. It typically roosts in trees, and sometimes in mangroves on small islands (Hoogstraal 1951, Rabor 1986, Heaney et al. 1998). There is generally high roost site fidelity (T. Mildenstein pers. comm. 2006), and roost sites are often located on steep slopes and cliff edges in areas that are difficult to access by humans. In mixed roosts of A. jubatus and P. vampyrus on Bohol, Boracay, Luzon, Mindanao, and Negros, A. jubatus was observed in the forest (away from the forest edge), whereas P. vampyrus were at the periphery, which might reflect a sensitivity of A. jubatus to disturbance (Mildenstein 2012, Gomez in litt. 2007).
A. jubatus is known to be forest-dependent based on studies of diet and habitat use (Mildenstein et al. 2005, Stier and Mildenstein 2005, Mildenstein 2012). Compared to co-roosting P. vampyrus, A. jubatus’ diet consists of a small subset of native forest tree species (N<20 species, Stier and Mildenstein 2005) focusing especially on hemi-epiphytic fig species, which may be a staple food item (Stier and Mildenstein 2005). A. jubatus preferentially selects primary and high-quality second-growth forest for foraging (Stier and Mildenstein 2005, Mildenstein et al. 2005). The species may occasionally leave this type of habitat, using streams where fig trees grow on banks, they rarely forage in orchards on agricultural trees (Mildenstein et al. 2005). On Mindanao, farmers believe that A. jubatus is a pest in fruit orchards, but this remains unverified, and it is possible that these individuals are misidentified P. vampyrus which are known to use orchards regularly (T.L. Mildenstein in litt. 2007).
THREATS
The species is threatened by severe habitat loss and hunting throughout its range, including within protected areas (Mildenstein 2012, L. Heaney pers. comm. 2006).
Habitat Loss
Acerodon jubatus is a known forest specialist based on studies of diet and habitat use (Mildenstein et al. 2005, Stier and Mildenstein 2005, Mildenstein 2012). Vegetative GIS layers and Bat Count surveys show that population sizes (for both A. jubatus and P. vampyrus) correlate closely with available natural forest cover, suggesting bat populations are habitat -limited (Mildenstein 2011, 2012). However, A. jubatus populations are much more sensitive to habitat loss and degradation due to their exclusive use of natural forest compared to Pteropus vampyrus’ included use of agricultural crops and degraded forest areas (Mildenstein 2012).
Most (>90%) of Philippines original old-growth forest cover has been destroyed (Kummer 1992). If current trends continue, no old-growth lowland forest will remain by 2030. Remaining total forest cover in the Philippines is roughly 10-15% secondary forest cover, much of this extant forest occurs above 1,000 m asl, where A. jubatus is unlikely to occur (L. Heaney in litt. 2007). Although there has been a moratorium on logging in the Philippines for over two decades, forest removal is on-going. In Samar and Pangasinan (Luzon), open-cast mines are removing forest cover (M. Pedregosa pers. comm. 2006) and in southwestern Negros, a roost of this species occurs in a copper and gold mining claim area (E. Alcala pers. comm. 2006). The forest area in Subic Bay Watershed Reserve has reduced by housing, commercial and tourist developments (T. Mildenstein, pers. comm. 2012). The roost on Polillo which occurs on privately owned land is also under threat from human disturbance (P. Alviola pers. comm. 2006) and the roost site on Boracay was displaced due to infrastructure development for tourism (M. Lorica pers. comm. 2006). Based on these current rates of deforestation, the future population trend for this species will depend on: 1) the extent of regenerating secondary forest, and 2) the ability of A. jubatus to persist in secondary forest (L. Heaney pers. comm. 2012).
Hunting
International trade data show that previously thousands of individuals of fruit bats were exported annually from the Philippines (Mickleburgh et al. 1992), many of these were likely to be A. jubatus. In 1995, the species were listed with other Pteropodids in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which brought about better enforcement of legislation, and increased efforts by customs in both Guam and the Philippines. The international trade of Philippine fruit bats is now minimal, although not altogether stopped (e.g. recent cases in Guam).
Hunting of flying foxes is illegal in the Philippines (except for the few remaining indigenous Aeta communities). However, fruit bat hunting is on-going and largely unregulated throughout the country. Reasons for hunting fruit bats in the Philippines vary. Fruit bats hunting is part of Filipino cultural heritage, and fruit bat meat is valued as a delicacy and/or for its medicinal properties (Cariño et al. 2006, Mildenstein 2012). Fruit bats may also be relied upon as an opportunistic food source for forest workers (Gomez in litt. 2007, T. Mildenstein and S. Stier pers. comm. 2012). Finally, fruit bats are valued for sport hunting and as ‘pulutan’ (any snack eaten while consuming alcohol) (Cariño et al. 2006, Mildenstein 2012). Depending on seasonal demands, local markets for fruit bats occur throughout the Philippines. Specific reports of local trade include on Negros Island, where individual bats can be sold for 15-30 pesos (0.30 -0.60US$) (Cariño et al. 2006), in Davao, Calinan province, Mindanao (N. Ingle pers. comm. 2004), at the mixed species roost at the prison at Sablayan (Mindoro) (H. Garcia pers. comm. 2006). In general, hunters and fruit bat buyers think of A. jubatus as quite odourous compared to P. vampyrus (S. Stier, pers. comm. 2012). In Bataan province and around Subic Bay (Luzon), A. jubatus is less preferred to Pteropus vampyrus because of this quality, but the species look similar, and hunters are generally not aware of which species they are taking (S.C. Stier in litt. 2007).
Hunters use lines with hooks (D. Balete pers. comm. 2006, L. Paguntalan pers. comm. 2011), shot guns, rifles, and air guns (T. Mildenstein, pers. comm. 2010, and A. Cariño in litt. 2007). The impact of hunting on fruit bat populations is greatest when it occurs at the roost site, which causes stress and risk of mortality across the entire colony. Species differ in their tolerance of roost site disturbance, with more specialized species expected to be more sensitive. A. jubatus populations exhibit a 12-fold reduction in population density when roost sites are unprotected compared to protected roosts with the same amount of surrounding habitat (Mildenstein 2012). Three roost sites (Boracay, Subic Bay, Luzon, and Mambukal, Negros) are formally protected from hunting by local landowners (Boracay) and the local government (Subic Bay and Mambukal), although occasional hunting is still known to occur at all three locations. At most other roost sites, A. jubatus experiences regular hunting pressure (Mildenstein 2012). Many flying fox colonies have moved from their original roosting sites due to hunting pressure (Mildenstein 2012), (e.g. Patag, Negros Occidental, Calinawan, Negros Oriental,Davao Oriental, Mindanao (A.B. Cariño pers. comm. 2007, Gomez in litt. 2007)).
Whether or not the roost site is protected from hunting, a large amount of hunting occurs away from the roosts during night-time foraging in protected and unprotected forests as well as farms kilometres from the roost. Nighttime hunting of bats away from the roost is known to be on-going in Subic Bay (S. Stier and T. Mildenstein pers. comm. 2001, M. Pedregosa-Hospadarsky pers. comm. 2010), Bohol (R. Pamaong-Jose pers. comm. 2011), Bilaran, Leyte (L. Paguntalan pers. comm. 2011), Mt. Malindang (Nuñeza et al. 2006), and Cebu (S. Ramayla pers. comm. 2011), and is likely to occur around all other roost sites containing this species (Mildenstein 2012).
Roost site disturbance
This species has been shown to be especially sensitive to disturbance at the roost site (Van der Aa et al. 2006, Mildenstein 2012). Even the three most-protected roosts, located on Boracay (off Panay Island), Subic (Luzon), Mambukal (Negros Occidental) are not especially protected from disturbance. All three lie within popular tourist areas, where they are subjected to disturbances caused by tourists and guides (e.g. clapping hands or deliberately tapping the roost trees to make them fly). In addition to causing more stress during a period when the bats are normally sleeping, there have been a number of reports of pups that got separated and abandoned due to disturbances at the roost site (Mildenstein 2012). Recent population estimates at these “protected” roosts show smaller populations compared to the 2000-2002 roost counts (Mildenstein 2012).
USE AND TRADE
International trade data show that previously thousands of individuals of fruit bats were exported annually from the Philippines (Mickleburgh et al. 1992), many of these were likely to be A. jubatus. Hunting of flying foxes is illegal in the Philippines (except for the few remaining indigenous Aeta communities). However, fruit bat hunting is on-going and largely unregulated throughout the country. Specific reports of local trade include on Negros Island, where individual bats can be sold for 15-30 pesos (0.30 -0.60US$) (Cariño et al. 2006), in Davao, Calinan province, Mindanao (N. Ingle pers. comm. 2004), at the mixed species roost at the prison at Sablayan (Mindoro) (H. Garcia pers. comm. 2006).
CONSERVATION ACTIONS
Current conservation efforts
The species is protected under the Philippine Wildlife Act (Republic Act No. 9147, 2001). A. jubatus has been included in Appendix I of CITES since 1995 (the species had previously been included in Appendix II since 1990). Although the species itself is formally protected, there is little enforcement of the protective legislation (N. Ingle pers. comm. 2011).
In addition, the majority of the species roosts are within formally designated protected areas, but most receive very little protection (S. Stier and T. Mildenstein pers. comm. 2001, M. Pedregosa-Hospadarsky pers. comm. 2010, R. Pamaong-Jose pers. comm. 2011, L. Paguntalan pers. comm. 2011, Nuñeza et al. 2006, S. Ramayla pers. comm. 2011, E. Breganza pers. comm. 2010, Mildenstein 2012).
Conservation needs/priorities
Clearly, one of the top priorities needs to be additional research on which we can base our conservation management decisions. We need to know more about where populations are extant, and we need to know much more about their current status. Long-term studies that track populations are very badly needed (L. Heaney pers. comm. 2011).
More focused conservation efforts are also urgently needed for this species throughout its range. Especially needed are the establishment and management of protected roosting areas, which are expected to result in a rapid increase in the number of bats at the roost sites (Mildenstein 2012). Protected flying fox roosts have the added benefit of being popular eco-tourist attractions, providing local communities with a source of pride, income, and a venue for learning about the natural heritage of the Philippines.
It is imperative that hunting prohibition for this species is enforced until research has been done to identify hunting impacts on population sizes and sustainable harvest levels. Conservation capacity-building, education and awareness within local communities and among local government units and non-profits are also essential to imparting the risks that this species faces and encouraging conservation management.
Although some captive breeding facilities exist, it is unclear if these are sufficient for re-enforcing wild populations. |
