|Scientific Name:||Rhinonicteris aurantia (Gray, 1845)|
Rhinonycteris aurantius (Gray, 1845)
|Taxonomic Notes:||The population in the Pilbara exhibits some differences to the northern population (Armstrong 2002, 2005, 2006; Armstrong and Coles 2007; K.N. Armstrong unpublished data), and awaits formal description (likely as a subspecies) (Churchill et al. 2008, Armstrong 2008). Issues with nomenclature were addressed by Simmons (2005) and Armstrong (2006). Note this species is part of the family Rhinonycteridae Gray, 1866 (see Foley et al. 2015).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Armstrong, K., Reardon, T., Woinarski, J. & Burbidge, A.A.|
This species is listed as Least Concern in view of its wide distribution across multiple regions of northern Australia, presence in a range of cave-bearing rocky landscapes, and presumed large population. There are persistent mining-related threats in the Pilbara region of Western Australia that have the potential reduce the size of the population there by more than 30% in the next two decades and to cause the loss of most known underground roosts in the next 50 years in the absence of mitigation (Armstrong 2011; Woinarski et al. 2014). However, while information on population size and the location of roost sites is poorly known in this region (Cramer et al. 2016), the species as a whole is considered to be secure. For cave-roosting bats that are reliant for their survival on suitable but relatively few roosts for half of every day, the area of occupancy is best considered as the total area of its roost sites only (excluding foraging habitat), given that area of occupancy can be defined as “the smallest area essential at any stage to the survival of existing populations of a taxon”. While this area is in the order of a few square kilometres and would probably allow a match to one of the highest threatened categories under Criterion B, the total number of known and inferred roost locations is greater than 10.
|Previously published Red List assessments:|
|Range Description:||This species is endemic to Australia where it is found in the Pilbara and Kimberley regions of Western Australia, the Top End of the Northern Territory, and north-western Queensland (Armstrong 2008; Churchill et al. 2008).|
|Range Map:||Click here to open the map viewer and explore range.|
The literature contains reports of colonies ranging in size from 20 to 25,000 individuals (Churchill 1991), but the larger numbers have not been verified with a robust counting technique, nor have they been noted in recent years. Large colonies are the exception, with only two currently known, and it is very likely that they number in the low thousands. Based on captures and the non-invasive quantification of activity near roost entrances, typical colony sizes range from a few individuals up to the low hundreds (K.N. Armstrong unpublished data). Rhinonicteris aurantia can appear relatively common in a locality because they are relatively simple to detect, either by active searching with a bat detector and taking advantage of their curiosity for small light sources, or by placing unattended bat detectors at cave entrances and relying on encounters following night visitation of non-roost caves. In reality, detections across an area might derive from widely ranging individuals that originate in a one or a few local roosts (K.N. Armstrong unpublished data). Suggestions of widespread commonality have not always been underpinned by effort to locate roost sites and estimate colony sizes (McKenzie and Bullen 2009), and hence there is still a relatively poor understanding of how limiting roost sites are across regions despite widespread records (Armstrong 2001; Cramer et al. 2016). Populations have not been connected across the Great Sandy Desert for many thousands of years (Armstrong 2006; Armstrong and Coles 2007), and movement within regional populations is probably related to the availability of suitable roosts that allow individuals to saltate across otherwise inhospitable landscapes (Armstrong 2001).
|Current Population Trend:||Unknown|
|Habitat and Ecology:|
Rhinonicteris aurantia roosts in caves and old underground mine workings in colonies of a few to several thousand individuals. Physiological studies have demonstrated that this species has one of the highest measured rates of pulmocutaneous water loss of any mammal and is unable to enter torpor (Baudinette et al. 2000), and thus it has an obligate requirement for warm, humid roost microclimates that are physiologically benign (Churchill 1991; Armstrong 2001). Deeper caves and mines that have the capacity to support these conditions are relatively uncommon in most rocky northern landscapes, which limits roosting opportunity, area of occupancy, and results in aggregations in relatively few subterranean structures. In the arid Pilbara region, bats will accumulate in the deepest structures during the hottest and driest parts of the year, spreading further afield when wetter conditions provide the opportunity for shallower caves to provide humid microclimates (Armstrong 2001). In the monsoonal north, the humid conditions probably allow more shallow caves to be used, and there have been rare reports of roosting in buildings. A suggestion of tree roosting is often quoted based on the comments of Churchill (1991, 1994), but this has never been confirmed in any population. In the Northern Territory both sexes accumulate into larger colonies to mate, but later in the breeding season many females disappear from known caves, and maternity colonies have not yet been observed in this region. Females give birth to a single young and lactation occurs in the wet season when insect availability is high (Churchill 1994).
Rhinonicteris aurantia are strong and highly acrobatic fliers, in contrast to many small hipposiderids bats, and forage in the open around vegetation (Bullen and McKenzie 2002), usually within a few metres of the ground (Churchill et al. 1988). They feed on a wide variety of insects, though mainly smaller moths and beetles and occasional seasonal abundances of groups such as isopterans (Churchill 1994). There is a possibility that they feed on accumulations of small insects at cave entrances (Cramer et al. 2016), possibly accounting for their commonly observed night visitation of underground structures that are not used during the day for roosting. They are normally observed foraging in gullies, gorges and larger watercourses, as well as open woodland and over hummock grasslands (Churchill et al. 1988; Armstrong 2001).
This species is well known to be very sensitive to roost intrusions and capture at roost entrances. Individuals will often vacate a roost following a disturbance, and the default assumption is that roost abandonment leads to higher rates of mortality because alternative suboptimal roosts nearby are less likely to provide suitable microclimates. Large numbers have also been killed by inappropriate cave gating in the past. A significant proportion of museum specimens originated as road kill, owing to their relatively low foraging height and curiosity for lights, which indicates that new roads close to roosts have the potential to deplete local colonies. The greatest threat to the species is the loss of roost sites that now serve as strongholds for a large proportion of the known population through the gradual deterioration and flooding of old mines and the possibility of catastrophic losses from sudden collapses (Armstrong 2001; Woinarski et al. 2014). The growing encroachment of iron ore mining also has the potential to remove roosts and thus area of occupancy in terrains where the species roosts in natural caves. Threats to roosting colonies appear to be of lower risk in the Kimberley and Northern Territory, but there is still the potential for catastrophic loss of large numbers if known important colonies are not managed effectively. While R. aurantia has a generalist diet and appears to use a range of habitats for foraging, widespread degradation of habitat quality around a roost, such as from poor fire management, might reduce colony survivability or place a limit on its size.
It is considered to be protected and secure in numerous protected areas in the Pilbara and Kimberley regions of Western Australia, Northern Territory and north-western Queensland, though several of the largest colonies are not in protected areas. Further studies are needed into the distribution, roost site locations, abundance, biology, and threats to this species (Cramer et al. 2016). A national conservation plan, incorporating a regional approach to management in the Pilbara region, would assist both mining proponents and government land managers (Armstrong 2001, 2010, 2011), and targeted, collaborative approaches between industry and wildlife managers for active management of stronghold colonies in underground mine workings and caves with colonies of significant size would help reduce the risk of losses from both insidious and catastrophic causes.
|Citation:||Armstrong, K., Reardon, T., Woinarski, J. & Burbidge, A.A. 2017. Rhinonicteris aurantia. The IUCN Red List of Threatened Species 2017: e.T19589A21998626.Downloaded on 18 November 2017.|
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