Description

The Pacific Sheath-tail bat is a medium sized bat with body size (nose tip – anus) ranging from 41-48 mm in males; and 44.4-45.5 mm in females. This species is sexually dimorphic, with females being larger than males. Their fur is brown in colour. The Pacific Sheath-tail bat can easily be distinguished from other bats in Fiji in that it has a very small tail, only just projecting from the flight membrane

Distribution

In the Pacific Region, this species is found in Palau, the Marianna Islands, Caroline Islands, Tonga, Samoa, American Samoa, and Fiji (including Rotuma). The subspecies E. s. semicaudata is restricted to Fiji, Samoa and Tonga. In Fiji,  the Pacific sheath-tail bat has been recorded from Rotuma, Ovalau, (Lomaiviti), Vatuvara Lakeba, Nayau, Cicia, Vanua Balavu (Lau), Yaqeta Island (Yasawas) as well as  Taveuni, Vanua Levu and Viti Levu.

Habitat Ecology and Behaviour

There is limited ecological data available for this bat simply because it has been very little studied The Pacific sheath-tail bat or Bekabeka, as it is known locally, is an insectivorous, nocturnal bat that roosts colonially in caves. They usually share their roosting caves with White rumped swiftlets (Aerodramus spodiopygius). The Pacific sheath-tail bats leave their caves in the hundreds at sunset to forage under forest canopy. Some Pacific sheath-tail bats have been observed foraging in village areas. Pacific sheath-tail bats, like other insectivorous bats use echo-location to catch their prey and navigate through obstacles at night. These bats can determine the size and nature of objects in front of them just by analysing the sonar echoes they receive from the objects.

Threats

The threats causing the decline of this bat across the Pacific are not well understood. Feral cats are a known predator, human visitation to caves is clearly another, forest loss and indiscriminate insecticide use may be another. Feral cats (Felis catus) are one of the main predators of the Pacific sheath-tail bat, and these have been observed waiting at the entrances of Pacific sheath-tail bat caves to intercept the bats as they leave the roosting caves. Inside the caves cats jump up and take bats from low roosting sites. Because of the Pacific sheath-tail bat’s dependence on native forest for food, the persistence of a population is threatened by deforestation, especially on small islands. The Pacific sheath-tail bat tends to forage under forest canopy which offers them protection against strong winds. Without forest protection, the bats are easily blown away from their foraging habitat (and food) by strong winds. The increased use of insecticides in forests and plantations reduces the availability of prey and increases mortality in these insectivorous bats (through consumption of sprayed insects). Increasing visits by people to caves is another significant problem and there is a low level of awareness of the vulnerability of these bats by those who start new ecotourism ventures and the like. The surviving populations in Fiji today can only be found in relatively inaccessible caves, highlighting the negative impact of human visitation to bat caves. Bats generally have a slow reproductive rate, meaning that there is a slow recruitment of the new, young bats into the current population. Slow reproductive rates combined with the threats of feral cats, deforestation and increased disturbance to add to the risk of extinction of these distinctive bats.

Conservation Status

The subspecies E. s. semicaudata, which is restricted to Fiji, Samoa and Tonga, is on the verge of extinction in the Samoas, while there is no recent information from Tonga. In Fiji, the Pacific sheath-tail bat is declining rapidly; it may already be lost from Viti Levu (last observed in 1979), Kadavu, and some smaller islands in the Fiji group. The Fiji Pacific sheath-tail bat populations have probably been in decline since the late 1950s. Caves that were occupied by these bats between 1960 and 1973, had low populations by 1978, and were empty by 2005. As mentioned above, these surviving populations are restricted to relatively inaccessible caves.

Remarks and Cultural Significance

The subspecies E. s. semicaudata, which is restricted to Fiji, Samoa and Tonga, is on the verge of extinction in the Samoas, while there is no recent information from Tonga. In Fiji, the Pacific sheath-tail bat is declining rapidly; it may already be lost from Viti Levu (last observed in 1979), Kadavu, and some smaller islands in the Fiji group. The Fiji Pacific sheath-tail bat populations have probably been in decline since the late 1950s. Caves that were occupied by these bats between 1960 and 1973, had low populations by 1978, and were empty by 2005. As mentioned above, these surviving populations are restricted to relatively inaccessible caves.

References

Flannery (1995);
Gilbert (1984);
Palmeirim et al. (2005);
Palmeirim et al. (2007);
Tarburton (2002);
Watling and Pernetta (1978).

Front Page Photo: Paddy Ryan