The Sheath-Tailed Bat of Seychelles

The Seychelles sheath-tailed bat is one of the world's rarest mammals. The Sheath-tailed bat 'Coleura Seychellensis' is one of only two mammals endemic to the Seychelles; this means that it cannot be found anywhere else in the world. Yet it is possibly the rarest bat in the world with only about 30-100 individuals left in Seychelles. It is one of the most endangered animals; fewer than 100 are believed to exist in the world. Very little is known about the bat’s ecology, habitat, roost, and behaviour. It has suffered from habitat deterioration due to the effects of introduced plant species.   'Coleura Seychellensis' is a sac-winged bat and occurs in the central granitic islands of the Seychelles Islands north of Madagascar. It probably was abundant throughout the Seychelles in the past, but it has declined drastically during the mid to late 20th century and is now extinct on most islands. The reasons for its decline are unknown. It has been suggested that the barn owl, 'Tyto Alba', introduced in 1949, may be responsible and also possibly predation by barn owls, roost disturbance, habitat loss and declines in insect availability resulting from use of pesticides. In the 1800s it was described as being common on Mahé but declined throughout the 1900s.  Today the known roost sites on Praslin and La Digue have all been abandoned.  The largest surviving roost is on Silhouette Island where two caves have been located.  These caves are part of a single system of passages in a boulder field.  Three small roosts on Mahé have been located.   At present it is listed as Critically Endangered by IUCN. It is the 25th EDGE (Evolutionarily Distinct and Globally Endangered) species listed by the Zoological Society of London. It is a trigger species for the Alliance For Zero Extinction highlighting the importance of Silhouette Island for the conservation of the species. If urgent conservation measures are not implemented soon, this species will become extinct.   The Silhouette roosts have been monitored by the Nature Protection Trust of Seychelles since 1997 and a study of the roost in 2003 recorded 32 bats.  This is the highest count of this species ever recorded in a roost and the low figure is an indication of the precarious status of this bat.  A second roost complex was discovered in 2005.   NPTS has installed an infra-red CCTV system into one roost so that monitoring can continue without disturbance to one of the world's rarest and least-known mammals. This is revealing important new information on the behaviour and ecology of this threatened species   This bat feeds on insects at night time using echolocation calls to detect objects and navigate. Its biology is mostly unknown. The bat echo locates at frequencies of 32-40kHz when commuting and feeding outside the cave, and at much lower, audible frequencies (15-20kHz) within the cave.   The weight of the bats averages about 11.1 g for parous females and 10.2g in adult males with a forearm length of about 55.6 and 53.9 respectively   Bats in the genus Coleura usually do not roost upside down but generally crawl into caves and houses, in crevices and cracks and press their undersides flat against stone walls. In the 1860's, it 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. It is insectivorous and colonies of bats are apparently divided into harem groups. It lives in both the Madagascar and Indian Ocean Islands Biodiversity Hotspot (Cons. Intl. 2005) and the Seychelles and Mascarene Islands Forests Global 200 Ecoregion. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)   The name "sheath-tailed" refers to the juxtaposition of the tail and the membrane that stretches between the hind legs, whereby the last half of the tail protrudes free from the membrane.  By adjustment of the hind legs in flight, the membrane can be lengthened or shortened as it slips over the tail, giving these bats precise manoeuvrability in flight.  They utilize acrobatic flight as they fly within the under story of the rain forest hunting both airborne and foliage-clinging insects. (Bonaccorso 1998) It has been the focus of recent intensive research which has determined that it is a species associated with small clearings in forests 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. The birth season occurs during the November - December rainy season. Relevant publications: Matyot, P. 1995  The sheath-tailed bat Coleura seychellensis Peters, 1868 (Chiroptera: Emballoneuridae) rediscovered on Silhouette island.   Phelsuma 4; 67-69 Rocamora, G. & F. Joubert 2004  Coleura seychellensis: monitoring.   Phelsuma 12 Joubert, F.  2004  Investigation into the ecology of the Seychelles sheath-tailed bat.   Phelsuma 12 Burgess, H. & N. Lee 2004  A behavioural study of the Silhouette sheath-tailed bat.   Phelsuma 12 Gerlach, J.  2004 The bats of Silhouette island, Seychelles.  Phelsuma 12 Gerlach, J.  2005  Invertebrates associated with the Seychelles sheath-tailed bat Coleura seychellensis.  Phelsuma 13 Gerlach J & Taylor, M. 2006 Habitat as a critical factor in the decline of the Seychelles Sheath-Tailed Bat Coleura seychellensis. Acta Chiopt.. 8; 129-139.