Sheath-tailed bat, the rarest bat in the world

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.

Sheath-tailed bat © Sinclair Laing

It was once commonly found in Seychelles, but the species has undergone a dramatic decline in population during the mid to late 20th century.  At present it is listed as Critically Endangered on the IUCN Red List. Without urgent conservation measures, this species will become extinct.

Little known

Very little is known about the bat’s ecology, habitat, roost, and behaviour. Several possible causes for its decline have been forwarded, including predation by barn owls, roost disturbance, habitat loss and declines in insect availability resulting from use of pesticides.

This bat feeds on insects at night time using echolocation calls to detect objects and navigate. Its biology is mostly unknown.  The weight of the bat is approximately 10.2g for males and 11.1 for females, with a forearm length of c. 53.9 and 55.6 respectively.  The bat echolocates at frequencies of 32-40kHz when commuting and feeding outside the cave, and at much lower, audible frequencies (15-20kHz) within the cave.

What needs to be done

Bats are often extremely good indicators of environment quality, thus their presence is related to the health of the habitat.  Decline in bats thus could suggest furthermore widespread concerns.   More research and studies are urgently needed to understand more about this species, and develop an action plan to save this rarest bat. Public awareness and education is also a possible way to improve the conservation status of the species.

Are we too late?

Biologists cannot determine a particular size in which the population of this species is no longer at risk of extinction, but many believe that for stable populations in stable environments, 500 individuals may be sufficient to guarantee long-term persistence of the population.  Is this possible for the Seychelles sheath-tailed bat to increase its population up to 500 individuals?

What has been done

Recent work under a project initiated by Nature Seychelles and implemented in collaboration with a group of universities in the United Kingdom confirm that previous populations of the sheath-tailed bat on Praslin and La Digue now appeared not to be present. However, the group has also discovered two previously unknown roosts. This study was able to present evidence that the sheath-tailed bat prefers mature tree stands for foraging.

The study reveals that habitat loss is not the only contributor to the decline of the species. This leads to the question of pesticide use and its’ link with prey availability.  The results also underline the importance of roosts and roost protection in bat conservation, as they represent not only shelter, but a conduit for social interactions, and an important foraging area. Therefore it is not simply the roost itself that needs to be protected but also the habitat surrounding each roost.

The result of the research will be published soon. Nature Seychelles is seeking for more funding to continue this study with the hope to reverse its fatal decline.