Introduction

Australia's mammal fauna is rich and extremely distinctive (^{Holt et. al 2013}). It is also diminishing very rapidly (^{Burbidge and McKenzie 1989}; ^{Burbidge et. al 2009}; ^{McKenzie et. al 2007}; ^{Woinarski et. al 2011}). Recognising conservation concern about that trend, we recently undertook the first comprehensive review of the conservation status of the Australian mammal fauna (all terrestrial and marine species and subspecies in Australia, its external territories and territorial waters) (^{Woinarski et. al 2014}). In this paper, we summarise some of the main findings of that review.

As Australia is a nation occupying an entire continent, such a national conservation overview is appropriate and can be related readily to national conservation management activity and legislation. We recognise that the conservation status of Australian mammal species has been assessed recently by the IUCN as part of a broader global review (^{Hoffmann et. al 2011}; ^{Schipper et. al 2008}), however that broad assessment has had little consequence for the conservation of Australian mammal species - for example, the global review resulted in no changes in the listing of threatened species under Australian national legislation, and provided no substantial management advice for the conservation of Australia's threatened mammals. Our objectives were: to provide an explicit focus on the conservation of Australian mammals; to provide information in a manner that would be most appropriately formatted for overhaul of the now somewhat sub-optimal listing of threatened species under Australian legislation; to assess the extent to which current conservation management actions were delivering benefits to Australia's threatened mammals; to identify major factors affecting the status of Australian mammals; and to identify research and management priorities.

The approach we adopted was modelled on comparable overviews of Australian birds, that sought to provide not only an assessment of the conservation status of all taxa but also to frame and guide a coherent conservation management response (^{Garnett and Crowley 2000}; ^{Garnett et. al 2011}). Our review was also substantially informed by now somewhat dated conservation assessments for particular groups of Australian mammals, including marsupials (^{Maxwell et. al 1996}), rodents (^{Lee 1995}), bats (^{Duncan et. al 1999}), cetaceans (^{Bannister et. al 1996}) and seals (^{Shaughnessy 1999}).

More so than most other areas, the status of Australian mammals can be benchmarked to a pivotal historical event, the first settlement of Australia by Europeans in 1788. Although a rich component of the Australian mammal fauna was lost before this date - most notably the extirpation of the extraordinary Australian megafauna over the period from about 60,000 to 20,000 years ago (^{Johnson 2006}) - European settlement saw a marked environmental transformation across many areas of Australia (^{Bradshaw 2012}) and the introduction of very many plant and animal species whose environmental impacts have been profound. Accordingly, we use 1788 as a baseline from which to chart the conservation fate of the Australian mammal fauna.

Material and methods

Our objective was to assess the conservation status of all Australian mammal taxa, using IUCN criteria (^{IUCN 2001}). These criteria mostly relate to distributional extent, and population size and trends. Accordingly, we required an inventory of all Australian mammal taxa, and information on the distribution and population of those taxa.

The taxonomy of Australian mammals is unsettled, with at least 50 endemic species described since 1970. We established a checklist of species and subspecies recorded in Australia and its external territories, based on consensus among a group of taxonomists working actively with Australian mammals, and in part informed by a far more comprehensive taxonomic treatment of the Australian mammal fauna in preparation (^{Jackson and Groves in press}). As evidence of the fluid nature of this taxonomy, six species of Australian endemic mammals (three bats (Mormopterus spp.) and three dasyurids (Antechinus spp.)) and a nearly-endemic coastal dolphin, Sousa sahulensis, have been described since 2012 (^{Baker et. al 2013}; ^{Baker et. al 2014}; ^{Baker et. al 2012}; ^{Jefferson and Rosenbaum 2014}; ^{Reardon et. al 2014}). The new Mormopterus species and the Sousa species were included in our review, but the new Antechinus were not considered, because their description post-dated our assessments.

There is no comprehensive distributional or monitoring data base for Australian mammals, although The Atlas of Living Australia (http://www.ala.org.au/) now provides a reasonable and increasingly comprehensive collation of distributional records. For our review, we collated distributional records for all terrestrial Australian mammal taxa from a wide range of state conservation agency and museum sources. This database used as a foundation a previous collation of mainland non-volant mammal records developed by ^{Fisher et. al (2014}), and added to it records of bats and Tasmanian mammals, from relevant data bases maintained by state agencies and museums. All resulting maps were inspected for outlying and potentially erroneous records, with any such records then referred back to the original source for confirmation or rejection. Subsequently, we used recent (post 1992) records to calculate area of occupancy and extent of occurrence, following ^{IUCN Standards and Petitions Subcommittee (2013)}. Distributional data for marine species were too meagre to allow for such analysis.

Reliable estimates of population size are available for only a few Australian mammal species (mostly large and commercially exploited kangaroo species, a few whale species, and a small set of highly localised threatened species). However, there is some information on trends in various measures of relative abundance for more species.

Based on this compilation of relevant conservation parameters, we assessed all taxa using IUCN criteria, as either Extinct, Critically Endangered (Possibly Extinct), Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern or Data Deficient. We allocated some taxa to Near Threatened (Conservation Dependent), a category no longer used by IUCN, but which is available under Australian legislation. These assessments related only to the Australian range of (the minority of) species that were not Australian endemics. This draft assessment and a detailed account were then widely distributed to additional relevant experts, and the assessments and accounts were reviewed in response to feedback. More than 200 experts provided such reviews. We used a cut-off date of December 2012 for all assessments, and also provided retrospective assessments (based on currently available information) of the conservation status of all taxa 10 and 20 years earlier. For extinct species, we documented the most recent record, and estimated the decade of extinction.

In addition to compiling information on these conservation parameters, we documented information on threatening factors for all taxa assessed as threatened or Near Threatened, rating threats according to the extent over which they operated (in relation to the distribution of the considered species), the intensity of their impact, and whether the threats were historical, current or projected.

Results

There is a marked distinction between the conservation status of Australian terrestrial and marine mammals (Table 1). Of 272 terrestrial Australian-endemic mammal species extant in 1788, we considered 28 are now extinct (Table 1, Table 2). A recent unsuccessful search for the highly localised (known only from a 5 ha cay) Bramble Cay melomys Melomys rubicola suggests that the number of extinctions is now 29, with that loss sometime since its last record, in 2009. In addition, the Christmas Island shrew Crocidura trichura was considered Critically Endangered (Possibly Extinct): with no records since 1985, it is likely now also to be extinct. Hence, in the 236 years since initial European settlement of Australia, more than 10 % of the endemic land mammal fauna has been rendered extinct. Our assessment concluded that the first post-1788 extinction was around the 1840s, and that the rate of extinction (of 1-2 species per decade) has continued unabated since then, with two species lost in the last 10 years (the Bramble Cay melomys and Christmas Island pipistrelle Pipistrellus murrayi).

Table 1 Tallies for the Australian conservation status of mammal taxa occurring in Australia. Conservation status codes: EX extinct; CR(PE) Critically Endangered (Possibly Extinct); CR Critically Endangered; EN Endangered; VU Vulnerable, NT(CD) Near Threatened (Conservation Dependent), NT Near Threatened; LC Least Concern; DD Data Deficient. 

* excludes DD taxa

Table 2 List of Australian mammal species assessed as extinct, threatened or Near Threatened in current review (MAP = Mammal Action Plan), ordered by conservation status. The conservation status (as at 2012) according to Australian legislation (EPBCA) and IUCN Red List is also given. Note that the Australian listing does not include a Near Threatened category. For MAP and EPBCA, the conservation status assigned relates (for non-endemic species) to only that part of their population in Australia or Australian waters. Conservation status: EX Extinct, CR(PE) Critically Endangered (Possibly Extinct), CR Critically Endangered, EN Endangered, VU Vulnerable, NT (CD) Near Threatened (Conservation Dependent), NT Near Threatened. 

* For both subspecies I. a. auratus and I. a barrowensis; ** as R. p. 'large form'; *** contested taxonomy, with some recent treatment as an endemic Australian species, C. dingo (Crowther et. al 2014); **** now recognised as S. sahulensis Australian Hump-backed Dolphin, but with unchanged conservation status in Australian range.

Our review assessed a further 55 Australian endemic land mammals as threatened (i.e. Critically Endangered, Endangered or Vulnerable), and a further 42 species as Near Threatened - i.e. 46 % of the Australian endemic terrestrial mammal species present in 1788 is now extinct, threatened or Near Threatened (Table 1, Table 2). The dominant trend for the threatened and Near Threatened species (for which such information was available) was for ongoing decline (with 38 terrestrial mammal species considered to have worsened conservation status over the period 1992 to 2012 and 11 species showing an improved conservation status over this period). Many species are now reduced to very small population sizes (e.g. nine species now have populations of fewer than 1000 individuals), or ranges that are now a minute proportion of their former distributions.

As recognised previously (^{Burbidge 1999}), islands have made a notable contribution to the conservation of Australia's mammals: seven species that have been lost from all of their former extensive mainland ranges have survived solely because subpopulations have persisted on continental islands. However, the fate of Australian mammals restricted to oceanic islands has been far less good: for these six species (five species endemic to Christmas Island and one to Lord Howe Island), four are now extinct, one is Critically Endangered (Possibly Extinct) and the remaining species (the Christmas Island Flying-fox Pteropus natalis) is Critically Endangered.

Also, as recognised previously, the fate of Australian mammals has varied between different taxonomic groups, sizes, ecologies and distributions (^{Burbidge and McKenzie 1989}; ^{Burbidge et. al 2009}; ^{Cardillo and Bromham 2001}; ^{Chisholm and Taylor 2007}; ^{Fisher et. al 2014}; ^{Johnson and Isaac 2009}; ^{Murphy and Davies 2014}). Medium-sized (ca. 35 g to 5.5 kg) mammals (such as larger dasyurids, larger rodents, smaller macropods, potoroids and bandicoots) have been most affected, arboreal species less affected, and declines and extinctions have occurred mostly in semi-arid, arid and temperate areas, with notable chronological variation. Previously considered relatively stable, the mammal fauna of much of northern Australia is now undergoing rapid and severe decline (^{Woinarski et. al 2011}).

Although individual species have differed in the pattern and cause of their decline (or extinction), and many factors may have contributed, the factor that has contributed (and continues to contribute) most to declines for terrestrial species has been predation by two introduced species, the European red fox Vulpes vulpes and feral cat Felis catus (^{Woinarski et. al 2014}). Other major factors implicated in decline include changed fire regimes, habitat loss and fragmentation, and habitat degradation due to introduced livestock and feral herbivores. The role of introduced disease is generally largely unknown, but there is some strong circumstantial evidence for some species (^{Abbott 2006}), and a particularly unusual (and currently untreatable) disease is entirely responsible for the current rapid decline of Tasmanian devil Sarcophilus harrisii, the largest remaining marsupial carnivore (^{McCallum et. al 2009}). Climate change has not yet had a major impact, but is projected to cause substantial declines for some species in some areas (particularly in tropical mountain rainforests and alpine areas; ^{Williams et. al 2003}).

In many cases, individual mammal species are, or have been, affected by multiple threatening factors operating synergistically at any one location, or differently across different parts of the species' range, or at different times. For example, in northern Australia, recent research has indicated that predation by feral cats has greater impact in areas exposed to more frequent and/or extensive fires (^{McGregor et. al 2014}). In south-western Australia, concerted management action has led to some benefit through reduction in the abundance of the European red fox, but that change in abundance has now led to increased impacts of predation by feral cats (^{Marlow et. al 2015}). Many species now face multiple threats: for example, the koala Phascolarctos cinereus is affected by disease (including Chlamydia and a retrovirus), predation by feral (and stray) dogs, timber harvesting, changed fire regimes, road traffic, habitat loss and fragmentation, drought and days of extreme heat.

Largely because of the identification and effective management of factors responsible for decline, some threatened terrestrial mammal species have shown some recovery over the last few decades. The most notable of these successes have involved translocation of individuals from remnant populations to islands or to intensively managed mainland areas (notably predator-proof exclosures) and broad-scale control of foxes (^{Woinarski et. al 2014}). Notwithstanding these efforts, the conservation status of only six terrestrial mammal species was considered to have been improved over the last 20 years.

For Australian marine mammals, the conservation status and outlook is far less clear. Only one species, the Australian sea lion Neophoca cinerea, is endemic to Australian waters. Of 58 species recorded from Australian waters, the information base for conservation parameters in these waters is so meagre for 35 species that no categorisation other than Data Deficient is justifiable. Many of these species may be imperilled or otherwise declining, but the evidence base is inadequate to demonstrate this. Several previously highly threatened species, most notably the Humpback Whale Megaptera novaeangliae, are recovering (and their conservation status was assessed as improving) in Australian waters following cessation of hunting (whaling or sealing). However, a wide range of threats - notably mortality from fisheries interactions, pollution, acoustic disturbance and habitat degradation - continues to affect most marine mammals in Australian waters, and it is likely that climate change and ocean acidification will lead to further declines.

Discussion

This review highlighted the disintegration of a diverse and highly distinctive mammal fauna over a period of little more than two centuries, and - alarmingly - concluded that the rate of loss is unabated. The number of extinct species is appreciably higher than previously recognised under Australian national legislation (where 20 Australian mammal species are currently listed as extinct) or from the most recent global assessment (22 Australian mammal species are currently categorised as extinct in the IUCN Red List). No other country has suffered such a high number of mammal extinctions over recent centuries. Many of the now-extinct mammal species were widespread, abundant and had broad habitat ranges at the time of European settlement (^{Hanna and Cardillo 2013}): they were unlikely candidates for extinction.

The Australian mammal fauna has shown a susceptibility to the impacts of introduced species, particularly two predators, that is characteristic of the frailty of island biodiversity generally (^{Alcover et. al 1998}). To some extent, conservation managers have now developed and implemented approaches that provide some control for one of these introduced predators, the European red fox, and sustained and large-scale conservation effort directed at this threat is achieving some impressive reversals of previous declining trends for some threatened species (^{Morris et. al 2003}). But to date there has been no successful landscape-scale control of the almost pervasive feral cat. The only remedial actions that have had some success against this threat have been localised and expensive predator-proof exclosures or translocations to cat-free islands.

Other intensive remedial conservation management has helped stave off extinctions for some high profile Australian mammal species faced with a range of sometimes idiosyncratic threats (^{McCallum et. al 2009}). However, much of the current decline in the Australian mammal fauna involves poorly-known low profile terrestrial species occurring in remote and ostensibly little modified areas, or is occurring largely unreported but incrementally for marine species, and there is little management attention to, or public awareness of the plight of, these species. Currently, there is insufficient knowledge of the status of many of these species, of the extent to which different threats are driving decline, or of management options to counter these threats. There are insufficient resources to manage the range of threats, and there is no coherent or consolidated response to address this crisis. Without major change in resourcing, management, policy and accountability, it is highly likely that this mammal fauna will continue to substantially erode.