Tiny Australian bat to go extinct within a year

The Christmas Island Pipistrelle at risk of extinction within one year

Courtesy of the Australasian Bat Society

The Christmas Island Pipistrelle, Pipistrellus murrayi, at just 3 g is one of Australia's smallest bats, and also one of its rarest. It is endemic to Christmas Island in the Indian Ocean, and is the only species of microbat on the island. Its distribution and abundance have declined dramatically in recent years, and as a result it was listed as ‘Critically Endangered' in 2006. Surveys undertaken in the mid-1980s found it to be common and widespread across the island. However, by the mid-1990s there had been a marked reduction in abundance and a westward range contraction. This decline continued at a rapid rate and the species is now confined to the far west of the island, no longer occurring across most of its former range.

99% decline since 1994 - Extinct within 1 year?
Long-term monitoring using ultrasonic bat detectors indicates this species has undergone a 99% decline in relative abundance since 1994. The number of individuals remaining is unknown, however based on recent observations it is possible there are less than 50 bats left. The monitoring data suggest that, if the current rate of decline continues, this species is likely to be extinct within the next year! If this occurs it will be the first Australian mammal extinction in 50 years. Australia has the worst record of mammal extinctions in the world: we do not want to add anther species to this list.

Cause of decline in unknown
The cause of this rapid decline remains unknown, despite the identification of a range of potential threatening processes. Extensive areas of habitat are available, with 75% of the island covered by primary or secondary rainforest. The pipistrelle is a generalist aerial insectivore and as there is an abundance of nocturnal flying insects, lack of food is unlikely to be the cause. Predation or disturbance at roost sites is considered one of the most likely threats to the survival of the species. Individuals roost in colonies under exfoliating bark on dead trees, many of which are heavily decayed and collapsing.

Possible threats - Yellow crazy ants?
Currently only one breeding roost site is known. A number of introduced species may be preying on, or disturbing bats from within their roosts, e.g. Common Wolf Snake Lycodon aulicus capucinus, Feral Cat Felis catus, Black Rat Rattus rattus and Giant Centipede Scolapendra morsitans. Although not considered the primary cause of decline, the recent explosion of Yellow Crazy Ants Anoplolepis gracilipes is likely to have exacerbated the situation. It is also possible that some form of disease may be contributing to the decline, however, with the exception of individuals having low white blood cell counts, there is little evidence for this.

Management actions - Little benefit so far
A range of management actions are currently being undertaken to monitor the population and control threatening processes, including installing protective barriers around the base of known roost trees, and establishing bat boxes in an attempt to provide additional roost sites. However, despite these efforts the population continues to plummet to a critical level.

Captive breeding potential
Recent reports have recommended the urgent establishment of a captive breeding program as insurance against further decline in numbers and as a source of individuals to re-establish wild populations once the cause of decline has been identified and controlled (James and Retallick 2007, Lumsden et al. 2007). In addition, it is critical that further studies are undertaken concurrently to determine the cause of the decline and to investigate management actions that can be undertaken now to slow the rate of decline.

One important management action is to ensure that Yellow Crazy Ant supercolonies are controlled in the remaining pipistrelle roosting and foraging areas. Particularly urgent is the location of more roosting sites to enable these trees to be protected from potential predators.

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