|Scientific Name:||Pteropus niger|
|Species Authority:||(Kerr, 1792)|
Vespertilio vampirus subspecies niger Kerr, 1792
|Red List Category & Criteria:||Vulnerable A3cd ver 3.1|
|Assessor/s:||Hutson, A.M. & Racey, P.A.|
Listed as Vulnerable based on a projected 30% population reduction in the next 21 years (three generations) due to the continuing decline in the extent and quality of a key habitat (forest, which is relied upon for roosting and at certain times of year for foraging); knowledge of impacts of past cyclones on this and other island fruit bats and the likelihood of this happening again on Mauritius within the next few years; and based on current pressures from hunting, which are likely to increase.
|Range Description:||Since becoming extirpated from Réunion in the early eighteenth century, this species has been restricted to the western Indian Ocean island of Mauritius (Bergmans 1999, Cheke and Hume 2008). There are occasional recent records on Réunion (see under Population). Cheke and Hume (2008) consider it possible that bats reported by Leguat in Rodrigues in 1691-1692 (Leguat 1708) might have been this species.|
|Range Map:||Click here to open the map viewer and explore range.|
There has been a range of population estimates (of total number of individuals) with the first estimate of 10,000 individuals in 1974 (Cheke and Dahl 1981). Cheke (pers. comm. 2012) admits that this was a very crude estimate based on counts of a few colonies and talks with hunters and other anecdotal sources. The Mauritian government states that it has carried out counts since 2003, and data are available for 2006 and 2010. These give figures of 22-25,000 for 2006 and 49-56,000 for 2010 (Sookhareea 2011) using a range of techniques depending on circumstances. The population figures given are for all animals: the numbers of mature individuals is estimated to be ca. 65% of the total population, hence 33,000 of an estimated population of 50,000, and 16,000 for a population of 25,000 (based on a 50% mortality in the first year, and a 30% mortality in subsequent years, with a period of at least two years to maturity and a generation time of seven years).
An additional estimate by Robin for 2007 suggests 12,000-16,000 (Robin 2007) using evening dispersal counts. The counts over the last 10 years have not been carried out in a consistent fashion and may not be directly comparable. Nevertheless, it is likely that there has been an increase in population in that time, although the scale of that increase is uncertain. An increase is likely since there has been no significant cyclone in that period, and major cyclones will result in heavy population losses, which will be slow to recover. The number of known roost sites has also increased from c.14 in 2003 (Nyhagen 2004) to c. 57 (Robin 2007, Sookhareea 2011). A methodology has now been established for counting all known roost sites and it is hoped that regular surveys will provide data to track the population trend.
In 2007 a small population (10-20 animals) was identified on Réunion (where the species formerly occurred, but has been extinct for well over 100 years). These animals can be assumed to have blown over from Mauritius (as suggested for other stray individual records since 2000). Limited erratic breeding has been demonstrated on Réunion, and so this population has not been considered for the purposes of this assessment.
|Habitat and Ecology:||
All roost sites known are in forest, mostly in the more forested parts of mountain ranges, in secure places with restricted access, leeward side and generally avoiding exposure to full sun (Sookhareea 2011). They comprise a few hundred trees (since each roost consists of a few tall trees), with accessible canopy structures, and with terminal branches strong enough to bear the weight of a few large bats. Five tree species are favoured, being a mixture of native and exotic species: Eucalyptus spp, Tecoma (Tabebuia pallida), Araucaria spp, Bois noire (Albizia lebbek), and the endemic Bois de natte (Labourdonnaisia spp). The roost may also be associated with or close enough to fruit trees of a wide range of species to feed on, plus a few trees in leaf to provide supplementary food when fruit and flowers are in short supply.
Roost sites represent day resting places. During the night the bats may travel for many kilometres around the island to very different habitats, including human habitation and orchards, to feed and then return to a roost site for the daytime. A number of animals collect at these roost sites, but they are highly vagile, and move often from roost to roost, often over large distances and for a variety of reasons, such as prevailing wind, food availability, stage of the reproductive cycle (bachelor roosts are described, and separate roosts for mothers and young). In Mauritius, the roosts in the north-west are much more heavily used during the dry season.So although roosts are often historic and used over many years, the number and composition of bats involved can fluctuate markedly (and may be none for part of the year), and historic roosts are often deserted after a major disturbance. Thus, although the roost sites are very important for conservation, and should be treated with reference to their contribution to the maintenance of the population as a whole, for the most part, they cannot be treated as individual units for the purpose of a Red List assessment. Robin (2007) grouped the roosts into North, East and West, which may have been partly due to their association with three principal mountain ranges, although it seems to have been principally for reasons of easing targeting of surveys; and Sookhareea (2011) separated the island into four regions: N,E,S,W, but also for purely practical reasons for survey purposes. In view of the nature of the major threats and the way the bats use the island, including the roost sites, and hence the inability of defining any number of discrete locations within Mauritius, it is considered that the number of locations for this species is one, corresponding to the island of Mauritius.
The results of molecular genetic studies of other island pteropodids shows they are panmictic and there is little evidence of population structuring.
Half the plant species that have been identified as contributing to the diet of the species are native and half exotic (Nyhagen 2004, Nyhagen et al. 2005). The bats turn to cultivated fruits when natural food sources are in short supply, particularly in the dry season (September to December). Without the mix of natural food sources and some exotic food sources it is likely that the population and breeding success of the bats would suffer to some degree. Thus there is a strong reliance on forest, both for roosting and for foraging. Foraging also takes place in plantations (orchards), small holdings and gardens when suitable fruit is available.
Like other Pteropus species in the region, this species is threatened by cyclones, the loss of roosting and feeding trees, and by persecution and/or hunting. Although no major cyclone has affected bats on Mauritius in recent years, the risk remains high and climate change forecasts suggest that there will be an increase in the frequency and intensity of cyclones in this region. Cyclone damage can result in high levels of starvation and mortality, as well as loss of roost trees. Elsewhere, such cyclones have caused massive declines (up to 99%) in island fruit bat populations. In the previous 10 years six intense tropical cyclones had affected Mauritius. Note that, for example, a cyclone in the 1970s reduced the population of the endemic fruit bat on the neighbouring island of Rodrigues to less than 1% of its current population (Powell and Wehnelt 2003). Similarly a cyclone in 1988 has been suggested as the cause of a decline of over 99% in the population of the endemic fruit bat of Christmas Island in the eastern Indian Ocean, but where, perhaps from a combination of factors, there has been little recovery since (Richards and Hall 2012).
Forest habitat suitable for roosting and important for feeding, particularly at certain times of year, have seen major decline of what is already a habitat much depleted in both area and quality (15-20% decline in the 10 years to 2005). While the significant holdings by government have shown little decline in recent years, private holdings have seen the majority of the declines, and that decline is likely to continue.
Page and D’Argent (1977) demonstrated that less than 2% of Mauritius’ native forest remained, and this was recognized in the Ministry of Environment and Sustainable Development’s 2006 Pocketbook of Environmental Statistics. Forest areas currently occupy about 25% of the total land area, but many of these areas are heavily invaded by exotic vegetation. A report Economic and Social Indicators, Environment statistics 2009, from the Central Statistics Office (quoted in National Economic and Social Council Report 17, 2011, Maintaining the Green Cover of Mauritius) identifies a loss of forest area amounting to a change of 5.1% of the total land area over the period 1995 to 2005. From the figures given, currently half the forest area is privately owned. The report identified loss to state owned forest of 1.5%, but a loss of 27.6% of privately owned forest. Very little change was identified for the four following years to 2009. The same report quotes from Digest of Environment Statistics 2009, CSO, giving a loss of forest, shrubs and grazing land of 10,000 ha (17.2%) between 1995 and 2005. The data suggests that the government is maintaining its own holdings, indeed Appendix 3 to this report identified a number of government initiatives for the maintenance, restoration and creation of forest areas, but at present these are mainly new and small initiatives and in no way compensate for the losses to privately owned forest.
Even if foraging area has increased following the wider introduction of fruit farms, especially for litchi, longan and mango, these are only available for a short period of the year and it is believed that there are times of year when the bats would not survive well without forest foraging.
Although protected, there is currently a level of control and sport hunting that is likely to be sustainable. However, there is increased pressure to reduce populations, through conflict with fruit growers at certain times of year. Any significant increase in the take of fruit bats is likely to have serious impact on the populations and combined with the other major threats described above could threaten the survival of this endemic species.
Estimates of existing levels of take for sport or as measures for pest control are given at about 2,000 bats per year. This is between 4 and 10% of the recent population estimates. Any introduction of a cull that would significantly reduce fruit bat damage to fruit (mainly litchi, longan and mango) must similarly impact on the bat population. Since the species is currently listed by IUCN as Vulnerable and is protected under Mauritian law (Wildlife and National Park Act 1993, currently under revision), the introduction of a cull is likely to result in the species being removed from the protected list and would be aimed at making a significant impact on the population, but is also very likely to increase the exploitation for sport and for unmanaged control. Hence, the moment a cull were introduced, it would immediately trigger the need for a re-evaluation of the status of the species. While no full analysis of sustainable take is available for such fruit bats it is widely considered that a take of 10% per year will result in significant population decline (e.g. Pierson and Rainey 1992).
There are no data on specific threats to specific roost sites, but the threats to bats at roost sites in Mauritius (principally deforestation, hunting and cyclones) can impact a number of roosts at one time and in no particular pattern. In the case of a larger cyclone a very large number of roosts can be damaged at the same time and which roosts are damaged will depend on details of the movement of the cyclone and its strength. These cyclones also affect the foraging of the bats, both around the roost site and elsewhere and there are many examples of where cyclone damage has resulted in high levels of starvation and mortality, in addition to damage to roost trees, in island-dwelling fruit bat species.
|Conservation Actions:||The species became a protected species in 1993 on Mauritius (Nyhagen et al. 2005). It is reported to occur in protected areas, including the Black River Gorges National Park (Nyhagen 2004), nature reserves and mountain reserves. This species is listed on Appendix II of CITES. There is a clear need to maintain monitoring of the population size, population dynamics, response to cyclones, assess fruit predation in relation to other predators and to the bats contribution to ecoservices, roosting habitat requirements, the impact of culling on this species, and the effectiveness of fruit protection to prevent foraging.|
|Citation:||Hutson, A.M. & Racey, P.A. 2013. Pteropus niger. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 10 December 2013.|
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