3 – The extent and adequacy of monitoring for Australian threatened mammal species^25Monitoring of extinctions in Australian mammals
Regrettably, extinction has been such a frequent occurrence in the Australian
terrestrial mammal fauna that there is value in monitoring its incidence, because
such monitoring can be informative about variation over time in the rates of
biodiversity loss, and the efficacy of conservation responses. Many measures of
environmental trends, such as State of the Environment reporting (State of the
Environment Committee 2011), use the length of lists of threatened species as a
marker of biodiversity trends. However, this tally has many constraints associated
mostly with a mismatch of unknown magnitude between the number of listed
threatened species and the actual number of species that are eligible for listing as
threatened; with this mismatch due in part to data deficiency and limited
resourcing that constrains the rate at which species can be assessed for
conservation status. To some extent, there is less interpretative uncertainty about
extinctions. However, there are some caveats even in the counting of extinction
events. Some species previously considered extinct have happily subsequently been
found to be extant (the ‘Lazarus’ phenomenon: Keith and Burgman (2004)). For
Australian mammals, there have been periods of incorrectly presumed extinctions
for at least the bridled nailtail wallaby Onychogalea fraenata, Christmas Island
shrew Crocidura trichura, Gilbert’s potoroo Potorous gilberti and Leadbeater’s
possum Gymnobelideus leadbeateri (Woinarski et al. 2014). Conversely, some
species have become extinct without such loss being recognised until long
afterwards. For example, the Capricorn rabbit-rat Conilurus capricornensis was
never reported as a living animal, but has recently been described from sub-fossil
material that probably post-dated European settlement (Cramb and Hocknull
Fig. 3.1. Monitoring extinction: the cumulative loss by decade (in the 10 years following the date shown) of
Australia’s terrestrial mammal species. Note that this graph excludes three species (Bettongia pusilla,
Conilurus capricornensis, Pseudomys glaucus) for which so little information is available that the decade of
extinction cannot be reliably estimated. Graph modified from Woinarski et al. (2014).