Rousettus obliviosus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Chiroptera Pteropodidae

Scientific Name: Rousettus obliviosus Kock, 1978
Common Name(s):
English Comoros Rousette, Comoro Rousette
French petite roussette des Comores, roussette des Comores
Taxonomic Notes: Rousettus obliviosus was previously considered to be a subspecies of R. madagascariensis (e.g., Peterson et al. 1995), but the two forms have been shown to be distinct species (Kock 1978, Goodman et al. 2010a).

Assessment Information [top]

Red List Category & Criteria: Vulnerable B1ab(iii)+2ab(iii) ver 3.1
Year Published: 2016
Date Assessed: 2016-05-30
Assessor(s): Sewall, B.J.
Reviewer(s): Mildenstein, T.
Contributor(s): Goodman, S., Van Cakenberghe, V., Granek, E.F., Mickleburgh, S., Hutson, A.M. & Bergmans, W.
The species has a limited range; both its extent of occurrence and area of occupancy are less than thresholds of 20,000 km² and  2,000 km², respectively (the minimum convex polygon including all three islands it inhabits is 9,085 km², and the total area of all three islands it inhabits is 1,783 km²). It is also known to exist at no more than ten locations (seven consistently-used roosting caves are known), and it is experiencing a continuing decline in the extent and quality of its habitat (due to increasing human pressures leading to substantial loss of native forests; ongoing loss of trees from plantations, orchards, and agroforestry areas; and increasing human disturbance at roost sites). Thus, the species is listed as Vulnerable under B1ab(iii)+2ab(iii).
Previously published Red List assessments:

Geographic Range [top]

Range Description:Rousettus obliviosus has been recorded only from the three islands of Grande Comore, Anjouan, and Mohéli of the Union of the Comoros, western Indian Ocean (Sewall et al. 2003, Louette et al. 2004, Goodman et al. 2010b). The species has been recorded from 30-1,750 m on Grande Comore, from 200 to 1,350 m on Anjouan, and from 10-700 m on Mohéli (Meirte 1984, Reason et al. 1994, Sewall et al. 2003, Goodman et al. 2010b). Since the highest points on these islands are 2,361 m, 1,595 m, and 790 m, respectively (Battistini and Vérin 1984), and since diverse canopy rainforest or cloud forest habitat is replaced by tree-fern, scrub, grassland, or heath habitat above 1,800 m on Mt. Karthala on Grande Comore (Louette et al. 2004), the bat species probably occurs from near sea level to about 1,800 m on Grande Comore, and across most of the elevational ranges of Anjouan and Mohéli. These records also suggest that the area of occupancy is less than the total area of the three islands (Sewall et al. 2003), which is 1,783 km² (Louette et al. 2004). Likewise, these records suggest that the extent of occurrence is less than the total area of the three islands and intervening unsuitable ocean habitat, which is 9,085 km². The species is apparently absent from Mayotte, the other large island in the Comoros Archipelago, as it has never been observed there despite extensive searching and trapping effort (Sewall et al. 2003, Louette et al. 2004, Goodman et al. 2010b).
Countries occurrence:
Additional data:
Estimated area of occupancy (AOO) - km2:1783Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):UnknownEstimated extent of occurrence (EOO) - km2:9085
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):Unknown
Number of Locations:7Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:UnknownLower elevation limit (metres):10
Upper elevation limit (metres):1800
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Rousettus obliviosus is rarely observed outside of research studies due to its nocturnal foraging and cryptic roosting habits. It has nonetheless been captured frequently by bat researchers (Reason et al. 1994, Clark et al. 1997, Sewall et al. 2003, Goodman et al. 2010b), and thus the species is considered fairly common (Reason et al. 1994, Louette et al. 2004, Goodman et al. 2010b). The true population size is unknown. The only abundance estimates available are from roost counts, and very few roost sites are known. Sewall et al. (2003) searched Grande Comore, Anjouan, and Mohéli and found or confirmed five permanent roosts plus a sixth that was intermittently used. They estimated that colony size at roosts ranges from around 100 to several thousand animals, and that the total population of these six sites was between 7,100 and 17,100 bats (Sewall et al. 2003). Since then, two additional roosts have been discovered, one small (~100 bats) and one mid-sized (~2,000 bats) (Hume and Middleton 2011, I. Saïd and W. Masefield pers. comm.). Thus, the current population at known roosts is estimated to number about 10,000 to 20,000 bats. Estimates of demographic parameters from genetic analyses suggest recent population stability in this species (Goodman et al. 2010a). Further, no genetic population structure is evident among the three islands, despite separation of at least 40 km of open water between adjacent islands; this indicates inter-island dispersal (Goodman et al. 2010a).
Current Population Trend:Unknown
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:The Comoros Islands harbour a distinct forest type of tropical moist broadleaf forest, part of the ‘Comoros forests’ ecoregion (Olson et al. 2001), which formerly served as the foraging habitat for R. obliviosus. However, nearly all large patches of this forest type, except in some higher elevations, have been destroyed. In parts of the remaining forest, the understory has been replaced by banana plantations, taro, or clove trees. R. obliviosus has been widely recorded as occurring in native forest, underplanted forest, and heavily-degraded forest within agricultural zones (Clark et al. 1997, Sewall et al. 2003, Goodman et al. 2010b). These records, and the presence in its diet of fruit from cultivated, non-native trees (Sewall et al. 2003), suggest that this species has thus far been able to exploit human-dominated landscapes – including agroforestry lands and orchards, as well as agricultural landscapes retaining remnant trees and forest patches – as foraging habitat. R. obliviosus has not been observed in villages or towns (Sewall et al. 2003, Goodman et al. 2010b).

Rousettus obliviosus is a cave-roosting species that is only known to roost in caves and shallow rock shelters in areas infrequently visited by people (Sewall et al. 2003). The species appears to be selective in roost sites, as it has been found in <20% of surveyed caves (Middleton 1998, 1999; Sewall et al. 2003; Hume and Middleton 2011; Middleton, pers. comm.; BJS, pers. obs.). Roosting habitat is either large lava tubes that are difficult to access or cave localities or shallow rock overhangs associated with streams or waterfalls in remote areas with steep terrain or dense vegetation (Sewall et al. 2003). Availability of such roosting habitat appears critical for this species. The lack of suitable roosting habitat on Mayotte may explain the absence of this species there (Goodman et al. 2010b) even though the species is capable of traversing open water over distances equal to that between Mayotte and its nearest neighbour, Anjouan (Goodman et al. 2010a).
Continuing decline in area, extent and/or quality of habitat:Yes
Movement patterns:Not a Migrant
Congregatory:Congregatory (year-round)

Use and Trade [top]

Use and Trade: Infrequent hunting has been recorded.

Threats [top]

Major Threat(s): Rousettus obliviosus has a limited range; its area of occupancy is less than the total area of the three islands (Sewall et al. 2003), which is 1,783 km² (Louette et al. 2004), and its extent of occurrence (including unsuitable ocean areas between the islands) is less than 9,085 km². It is therefore susceptible to single threatening processes, like cyclones, that could simultaneously or rapidly affect its entire range.

The major threat to the species within this range appears to be disturbance at roost sites. The bats appear highly susceptible to human disturbance, and infrequent hunting and rock falls in unstable lava tubes have been recorded at roost sites (Middleton 1998, 1999; Sewall et al. 2003). Additionally, cave surveys between 2000-2005 revealed the bats were absent from three caves where they apparently formerly occurred (Sewall et al. 2003, W. Masefield, pers. comm.), though it is unclear whether this suggests intermittent use of some roost sites or abandonment after disturbance.

Over the last few decades, the Comoros have undergone a sustained, rapid deforestation, resulting in the loss of nearly all its native forests. During the past 20 years alone, the country has lost 75% of its remaining forests, the fastest rate of any country in the world (UNDP 2013). Human pressures on native forests are expected to continue, as the growth rate of the human population remains high at 2.5% (UNDP 2013). Because R. obliviosus is regularly recorded in human-modified landscapes, loss of foraging habitat via deforestation is possibly not a major threat (Bergmans 1994). However, even human-modified landscapes containing non-native and remnant native trees are disappearing in the Comoros to make room for ground crops (FAO 2010, BJS pers. obs.); thus food resources for this species have probably been declining in recent years. Further, the loss of natural and underplanted forests may reduce its ability to cope with droughts and cyclones, and may limit its access to food resources when fruit from horticultural species is unavailable (Sewall et al. 2003). In addition, the replacement of native forests with agricultural land on Anjouan and Mohéli may render formerly inaccessible roost sites on Anjouan and Mohéli more easily reached, possibly exposing roosts to increased levels of human disturbance. Finally, the loss of native forests has resulted in impermanence or complete drying of nearly all rivers on Anjouan and most on Mohéli (Louette et al. 2004). R. obliviosus roosts on those islands are typically near waterfalls, and it is unclear whether that is simply where suitable caves and rock shelters occur or if the bats benefit from the adjacent water source. The species could benefit from an adjacent water source if, for instance, local humidity reduces evaporative water loss in the normally hot climate of the Comoros. If so, then it is possible the seasonal or year-round loss of water flow could affect this species on Anjouan and Mohéli as well.

Conservation Actions [top]

Conservation Actions: Rousettus obliviosus receives the highest level of legal protection available in the Union of the Comoros. It is listed as an ‘integrally-protected species’ (list 1 of RFIC 2001), which prohibits the capture or detention of R. obliviosus individuals without a permit. This law also expressly prohibits the killing of members of the Family Pteropodidae (flying foxes); transport, purchase, sale, export or re-export of living or dead individuals or their body parts; all disruption during the period of reproduction and raising of young; and the destruction of roosts (RFIC 2001). The Union of the Comoros also ratified the Convention on Biological Diversity in 1994, and in response has developed a National Biodiversity Conservation Strategy (Roby and Dossar 2000). This strategy highlights the importance of, threats to, and conservation recommendations for fruit bats of the Union of the Comoros (Sewall and Granek 2000). In practice, however, there are currently no direct conservation actions in place for R. obliviosus, and no formal terrestrial protected areas in the country.

The national Conservation Action Plan for Pteropus livingstonii (Sewall et al. 2007), another threatened pteropodid from the Comoros, includes an appendix for the conservation of Rousettus obliviosus. This appendix addresses current and potential emerging threats to R. obliviosus, and recommends five targeted conservation actions for R. obliviosus. Specifically, it recommends (1) protection of roost caves, especially the caves with the largest known colony on each island (these are now thought to be Panga Chilamouinani near Fassi on Grande Comore, Bakomdrundru near Ndrondroni on Mohéli, and Mangua Mitsano near Limbi on Anjouan); (2) discouraging, through environmental education, the hunting of all fruit bats; (3) conducting a comprehensive field search for more roost sites; (4) providing incentives to individuals owning land near roost sites to conserve caves and bats; and (5) devising a suitable population monitoring protocol and conducting regular visits to all known roost sites to track population changes (Sewall et al. 2007). Other key actions for this species include efforts to prevent further native forest habitat loss and additional studies designed to track the species’ population and inform its management (Sewall et al. 2003).

Citation: Sewall, B.J. 2016. Rousettus obliviosus. The IUCN Red List of Threatened Species 2016: e.T19757A101292795. . Downloaded on 19 September 2018.
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