Overview

Brief Summary

Biology

Until recently very little was known about this rare Seychelles bat. Colonies roost in caves and are thought to be divided into harem groups that consist of adult females and their young and are led by a single male (2). Unlike the African sheath-tailed bat C. afra (2), the Seychelles species hangs upside down from the cave ceiling to roost. Females give birth to their offspring during the rainy season that runs from November to December (2). These bats feed exclusively on insects (3) (7) (8).
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Description

The Seychelles sheath-tailed bat is one of the world's rarest mammals. These small bats are a reddish-brown colour with paler underparts (2). The name 'sheath-tailed' refers to a membrane that extends between the hind legs and can be placed over the tail. This provides precise movement in flight between the rainforest trees of their habitat (3).
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Distribution

Range Description

This species is endemic to the Seychelles, and is currently found on the islands of Silhouette, Mahé (in the northwest of the island) and Praslin. It is thought to have become extinct on La Digue island and Praslin since 1980s (Justin Gerlach pers. comm. 2008).
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Range

Endemic to the Seychelles islands of Mahe and Silhouette in the Indian Ocean, with historical records also from Praslin and La Digue islands (4). Total numbers are thought to range between 30 and 100 individuals (5).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
This species has been recorded from coastal boulder field caves with stable cool temperatures and access into native palm woodland or marsh habitat (Gerlach and Taylor 2006). It appears to need boulder caves with horizontal ceilings; low, stable temperatures; and clear cave flyways not obscured by vegetation (Gerlach and Taylor 2006). Joubert (2004) and Gerlach and Taylor (2006) provide specific details on the ecological requirements of this rare species. Although the species has recently been recorded from three islands, the only occupied roosting localities are known at La Passe and Grande Barbe (their continued presence at this second site was recently confirmed by J. Gerlach pers. comm.), on Silhouette island (Rocamora and Joubert 2004; Gerlach and Taylor 2006), and from two sites on Mahé, the main locality of Cap Ternay containing between 20 and 30 animals, and Anse Major with one or two bats (J. Gerlach pers. comm. 2008). Abandoned roosts have been recorded from all four islands in the species historical distribution. A detailed study of the roosting site at La Passe is provided by Burgess and Lee (2004).

Systems
  • Terrestrial
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Roost sites are located in coastal boulder field caves with stable cool temperatures and access to palm woodland or marsh habitat (4) (6).
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
CR
Critically Endangered

Red List Criteria
C2a(i)

Version
3.1

Year Assessed
2008

Assessor/s
Gerlach, J., Mickleburgh, S., Hutson, A.M. & Bergmans, W.

Reviewer/s
Hutson, A.M., Racey, P.A. (Chiroptera Red List Authority) & Cox, N. (Global Mammal Assessment Team)

Contributor/s

Justification
Listed as Critically Endangered because its population size is estimated to number fewer than 250 mature individuals, with no subpopulation greater than 50 individuals, and it is experiencing a continuing decline.

History
  • 2004
    Critically Endangered
  • 1996
    Critically Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
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Status

Classified as Critically Endangered (CR) on the IUCN Red List (1).
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Population

Population
The species was noted by Wright (1868) to be 'very common in the neighborhood of the town of Port Victoria'. Joubert (2004) mentions that the species was seemingly still abundant up to the 1970s, and that the use of guano deposits as an indicator suggests that the magnitude of decline may have been as high as 90%. The global population is now clearly very small, and although the precise number is not known, it is believed to be fewer than 100 mature individuals (Rocamora and Joubert 2004; J. Gerlach pers. comm. 2008). The roosting cave at La Passe was recorded to contain 32 bats in total in 2003 (Gerlach 2004, 2008), however, more recently only 27 animals have been recorded roosting at this locality (Justin Gerlach pers. comm. 2008).

Population Trend
Decreasing
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Threats

Major Threats
Gerlach and Taylor (2004) report that the most catastrophic decline of this species probably occurred in the late 1800s and early 1900s when lowland forests were cleared, converting the mosaic of woodland and open gaps to intensively managed coconut plantations with no shrub layer to support the invertebrate diet of this species. Invasive plants including the Kudzu vine (Pueraria phaseoloides) and coconut scrub from abandoned plantations threaten remaining suitable habitat for this species. Kudzu vine threatens to overgrow roost cave entrances or to change the temperature gradient within caves (Gerlach and Taylor 2004). The species is sensitive to disturbance of roosting caves and this remains a threat to any active roost sites. Other suggested threats have been the predation of bats by the barn owl, Tyto alba, introduced in 1949, and feral cats.
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The Seychelles sheath-tailed bat has been lost from the majority of islands where it was originally found. The precise cause of this dramatic decline is unclear; it has been speculated that introduction of the predatory barn owl (Tyto alba) and declines in insect availability resulting from use of pesticides may be involved (3). However, the recent discovery of a second roost near marshes on Silhouette showed that the bats here feed on different insects than those eaten by roosts that forage in palm woodlands elsewhere (4). It has therefore been argued that this variability in the diet demonstrates that food is not a limiting factor for the species, and the decline in the species may rather be attributable to habitat alteration caused by invasive plants obstructing roost entrances (4).
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Management

Conservation Actions

Conservation Actions
Rocamora and Joubert (2004) recommend annual census of individuals along established transects; regular sensitive visits to all known roosting localities with additional surveys to locate any additional sites; reevaluation of the species distribution every three or four years; legal protection of all known roosting sites and their immediate surroundings; control of introduced predators (barn owl Tyto alba and cats); habitat protection within known feeding areas; public awareness campaigns; ongoing and additional research into the distribution, ecology and threats to this species. Gerlach and Taylor (2006) also outline the importance of removing invasive vegetation from existing and abandoned roost sites, and restoring lowland forests through the control of coconut and cinnamon, and replanting native vegetation.
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Conservation

The Nature Protection Trust of the Seychelles has monitored the known population of Seychelles sheath-tailed bats since 1997 (5) (6). As with other bats, the protection of roosts and foraging habitat are of great importance. Existing roosts must be preserved, not only from human disturbance, but also from introduced plant species that smother the cave entrances (4). To this end, one roost site had the invasive Kudzu vine Pueraria phaesolides cut back from its entrance in 2001 and 2004, and ongoing management aims to completely remove the species from the area (4). It is hoped that removal of invasive creepers from existing and abandoned roost sites will help to increase the desperately low numbers of this critically endangered bat to more sustainable levels.
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Wikipedia

Seychelles sheath-tailed bat

The Seychelles sheath-tailed bat, Coleura seychellensis, is a sac-winged bat. It occurs in the central granitic islands of the Seychelles. It was probably abundant throughout the Seychelles in the past[citation needed], but it has declined drastically and is now extinct on most islands.

It is one of the most endangered animals, fewer than 100 are believed to exist in the world. The Seychelles sheath-tailed bat has suffered from habitat deterioration due to the effects of introduced plant species. The largest surviving roost is on Silhouette Island, although small roosts do exist in Mahé and also Praslin and La Digue islands. Its lifespan is 20 years and also its length is 55–65 millimetres (2.2–2.6 in).[citation needed] It finds its mates by fighting with another male bat in front of the females.

The weight of Seychelles sheath-tailed bats averages about 10–11 grams (0.35–0.39 oz). Bats in this genus generally roost in caves and houses, in crevices and cracks. In the 1860s, the Seychelles sheath-tailed bat was reported to fly around clumps of bamboo towards twilight, and in the daytime to be found roosting in the clefts of the mountainside facing the sea and with a more or less northern aspect. These hiding places were generally covered over with the large fronds of endemic palms. The Seychelles sheath-tailed bat is insectivorous. Its colonies are apparently divided into harem groups.

It has been the focus of recent intensive research, which has determined that it is a species associated with small clearings in forest where it feeds on a wide variety of insect species. Observations of coastal or marsh feeding are thought to be bats that have been forced into feeding in unusual situations due to habitat deterioration. Although the species is not a specialist and has a high reproductive potential it is very vulnerable to disturbance and requires several roost sites within healthy habitat.

References[edit]

  1. ^ J. Gerlach, S. Mickleburgh, A. M. Hutson & W. Bergmans (2008). "Coleura seychellensis". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved June 1, 2012. 

Further reading[edit]

  • Burgess, H. & N. Lee (2004). "A behavioural study of the Silhouette sheath-tailed bat (Coleura seychellensis)". Phelsuma 12: 69–77. 
  • Gerlach, J. (2004). "The bats of Silhouette Island, Seychelles". Phelsuma 12: 78–90. 
  • Gerlach, J. & M. Taylor (2006). "Habitat as a critical factor in the decline of the Seychelles Sheath-Tailed Bat Coleura seychellensis". Acta Chiopterologica 8: 129–139. 
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