The very last Xmas island Pipistrelle bat was heard on 25 August 2009 with no further ‘sightings’ (hearings) despite intensive efforts to locate the species.
At 3 g it was/is the smallest bat in Australia. Writing in January 2009 Dr Lindy Lumsden noted:
“Surveys undertaken in the mid-1980s found it to be common and widespread across the island (Tidemann 1985). However, by the mid-1990s there had been a marked reduction in abundance and a westward range contraction (Lumsden and Cherry 1997, Lumsden et al. 1999). 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 (James and Retallick 2007, Lumsden et al. 2007). Long-term monitoring using ultrasonic bat detectors indicates this species has undergone a 99% decline in relative abundance since 1994 (James and Retallick 2007, Lumsden et al. 2007, Parks Australia North Christmas Island unpublished data…
…A reassessment of the number of individuals remaining in January 2009 suggests there could be as few as 20 individuals left. The only known communal roost contains only four individuals. Three years ago there were 54 individuals in this colony and there were several other known, similar-sized colonies.
“It is critical therefore that a captive breeding program is established immediately 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). An emergency rescue program has been proposed that will attempt to catch the remaining individuals to form the basis of a captive colony. It is essential this is undertaken within the next 3 months (i.e. by March 2009) – leaving it any longer than this there is a risk there will be so few animals left that it will not be possible to catch them.” http://batcall.csu.edu.au/abs/ChristmasIsland/PipistrellusmurrayiJan_09.htm
Lumsden predicted that the bat would be effectively extinct in June 2009. Possible causes of the decline include predation or disturbance by the Common Wolf Snake (Lycodon aulicus capucinus); predation by the introduced Black Rat (Rattus rattus), Feral Cat (Felis catus) or Nankeen Kestrel (Falco cenchroides); predation and/or disturbance by the Yellow Crazy Ant (Anoplolepis gracilipes) (or even pesticides used to control them); predation and/or disturbance by the Giant Centipede (Scolapendra morsitans); predation by endemic predators; habitat loss; habitat alteration; loss of roost sites; prey availability; climatic conditions; vehicle-related mortality; introduced disease and stochastic effects from decreasing population size.
Urgent efforts to establish a captive breeding campaign took until August 2009 to negotiate bureaucratic permissions. Despite their intensive efforts teams found 1 bat left, but unfortunately it vanished one night and was never heard again.
When asked what she felt about never hearing the last bat again Dr Lumsden said: “all of my predictions have come true…in January  I said it would be totally gone by June… my gut feeling was just telling me: that’s it, it’s gone” (For more on the story (and other bat stories) see the 360 degree radio composition: Give a bat a bad name http://www.abc.net.au/rn/360/stories/2010/2953118.htm)
It is still listed as critically endangered on the Commonweath EPBC Act site http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=64383 but the pipistrelle bat would seem to be the first Australian mammal known to have become extinct since the crescent nail-tail wallaby in 1956.