Survey guidelines for Australia’s threatened non-flying mammals

Arnhem Land rock rat

Zyzomys maini

States and territories: Northern Territory.

Regions: Localised in Kakadu National Park and other locations in the sandstone massif of western Arnhem Land, Top End of the Northern Territory.

Habitat: The primary habitat is patches of floristically-rich monsoon rainforest with thick leaf litter often where there is seepage amongst boulders on steep slopes at the base of cliff lines and boulder beds of gorges within the Arnhem Land Plateau (Woinarski & Fleming 2008). Typically it occurs in terrain where there are many caves, crevices or boulders and may also be found in adjacent habitats such as sandstone heathlands and hummock grasslands (Woinarski et al. 1992). However, it is absent from many monsoon rainforest patches due various factors, including a lack of suitable food trees, absence of rocky habitat or possibly as a result of unknown interrelationships with adjoining habitats that may form important secondary habitat. The Arnhem Land rock rat also occurs in the wetter, more heavily vegetated parts of sandstone areas with scattered eucalypts (Woinarski & Fleming 2008).

Habit: Ground-dwelling (possibly shelters in rock crevices).

Avg. body weight: 94 g (Woinarski & Fleming 2008).

Activity pattern: Nocturnal.

Diet: Predominantly feeds on the seeds of various species of rainforest trees and perennial grasses (Begg & Dunlop 1980). Larger hard-shelled seeds are collected on the ground and carried to crevices in rocks where they are consumed (Begg & Dunlop 1980).

Breeding: Breeds throughout the year, with a peak of pregnant and lactating females between March and May (Begg 1981a). Litters comprise two or three young and most females only breed once per year (Begg 1981a). Reproductive output is reduced for at least a year following fire (Begg et al. 1981).

Description

The Arnhem Land rock rat was formerly considered to belong to the same species as the Kimberley rock rat Zyzomys woodwardi until a taxonomic revision recognised the Arnhem Land rock rat as a separate species (Kitchener 1989). It is one of three species of large rock rats that occur in the monsoonal tropics of northern Australia, with this species confined to the Arnhem Land Plateau of the Northern Territory. The extent of occurrence is unknown and within its range the species appears to be highly fragmented and very patchily distributed (Woinarski 2000). This distribution pattern is partly a result of its preferred monsoon rainforest habitat being patchy (Russell-Smith et al. 1993) and the topographic complexity of the deeply dissected western Arnhem Land Plateau. Even within patches of its preferred habitat this species may be absent. Within its patchy distribution, it occurs in sub-populations with very little genetic exchange between locations (Woinarski 2006). Long-term monitoring indicates that this species has significantly declined by as much as 83 per cent in some areas, which may be related to the increasing incidence of broad-scale ‘hot’ fires on the Arnhem Land Plateau (Woinarski et al. 2002; Watson & Woinarski 2003, 2004).

Survey methods

On the basis of previous surveys, the following survey techniques are recommended to detect the presence of the Arnhem Land rock rat in areas up to 5 hectares in size:

• 
  daytime searches for potentially suitable habitat resources such as rock overhangs, crevices and boulders with a floristically-diverse monsoon overstorey and dense leaf litter cover (description of the survey technique and recommended effort is provided in Section 3.1)
  
• 
  collection of predator scats, owl casts or remains in predatory bird/mammal nests/dens (description of the survey technique and recommended effort is provided in Section 3.2)
  
• 
  daytime searches for signs, particularly of partially chewed seed husks under rock crevices, overhangs and boulders (description of the survey technique and recommended effort is provided in Section 3.2)
  
• 
  Elliott A trapping surveys conducted according to the technique description and recommended effort provided in Section 3.3.8. However, Zyzomys species are particularly susceptible to tail stripping when trapped, and should be handled with care. Such surveys could also be conducted with a combination of cage (description of the survey technique and recommended effort is provided in Section 3.2) and Elliott traps, and
  
• 
  placement of baited camera traps (same as for predator pads) in suitable habitat, particularly in remote locations (description of the survey technique and recommended effort is outlined in Section 3.3.6).
  

Similar species in range

The Arnhem Land rock rat overlaps in range with the common rock rat Zyzomys argurus from which it can be distinguished by its larger size (the average weight of the common rock rat is 36 g [Fleming 2008]); the tail length, which is about the same as head body length rather than noticeably longer (average 146 millimetres in Z. maini compared to 108 millimetres in Z. argurus); denser fur; more extensive occurrence of long hairs on the tail; colour (more grey than brown); and, where the two species occur in sympatry, the Arnhem Land rock rat primarily occurs in the wetter, more heavily vegetated terrain (Woinarski & Fleming 2008).

References

Begg, R.J. 1981a. The small mammals of Little Nourlangie Rock, NT. IV. Ecology of Zyzomys woodwardi, the Large Rock-rat and Z. argurus, the Common Rock-rat (Rodentia: Muridae). Australian Wildlife Research 8: 307-321.

Begg, R.J. 1981b. The small mammals of Little Nourlangie Rock, NT. II. Ecology of Antechinus bilarni, the Sandstone Antechinus (Marsupialia: Dasyuridae). Australian Wildlife Research 8: 57-72.
Begg, R.J. and Dunlop, C.R. 1980. Security eating, and diet in the Large Rock-rat, Zyzomys woodwardi (Rodentia: Muridae). Australian Wildlife Research 7: 63-70.
Begg, R.J., Martin, K.C. and Price, N.F. 1981. The small mammals of Little Nourlangie Rock, NT. V. The effects of fire. Australian Wildlife Research 8: 515-527.
Fleming, M.R. 2008. Common Rock-rat Zyzomys maini. In ‘The Mammals of Australia’ (Eds. S. Van Dyck and R. Strahan) pp. 652-654. (Reed New Holland: Sydney).
Kerle, J.A. and Burgman, M.A. 1984. Some aspects of the ecology of the mammal fauna of the Jabiluka area, Northern Territory. Australian Wildlife Research 11: 207-222.
Kitchener, D.J. 1989. Taxonomic appraisal of Zyzomys (Rodentia, Muridae) with descriptions of two new species from the Northern Territory, Australia. Records of the Western Australia Museum 14: 331-373.
Menkhorst, K.A. and Woinarski, J.C.Z. 1992. Distribution of mammals in monsoon rainforests of the Northern Territory. Wildlife Research 19: 295-316.
Russell-Smith, J., Lucas, D.E., Brock, J. And Bowman, D.M.J.S. 1993. Allosyncarpia-dominated rain forest in monsoonal northern Australia. Journal of Vegetation Science 4: 67-82.
Watson, M. and Woinarski, J. 2003. Vertebrate monitoring and resampling in Kakadu National Park 2002. Report to Parks Australia North. Parks and Wildlife Commission of the Northern Territory, Darwin.
Watson, M. and Woinarski, J. 2004. Vertebrate monitoring and resampling in Kakadu National Park 2003. Report to Parks Australia North. Parks and Wildlife Commission of the Northern Territory, Darwin.
Woinarski, J.C.Z 2000. The conservation status of rodents in the monsoonal tropics of the Northern Territory. Wildlife Research 27: 21-35.
Woinarski, J. 2006. Threatened Species Information Sheet: Arnhem Rock-rat, Zyzomys maini. Department of Natural Resources, Environment and the Arts, Darwin.
Woinarski, J.C.Z., Braithwaite, R.W., Menkhorst, K.A., Griffin, S., Fisher, A. and Preece, N. 1992. Gradient analysis of the distribution of mammals in Stage III of Kakadu National Park, with a review of the distribution patterns of mammals across north-western Australia. Wildlife Research 19: 233-262.
Woinarski, J., Watson, M. and Gambold, N. 2002. Vertebrate monitoring and resampling in Kakadu National Park. Parks and Wildlife Commission of the Northern Territory, Darwin.
Woinarski, J.C.Z. and Fleming, M.R. 2008. Arnhem Land Rock-rat Zyzomys maini. In ‘The Mammals of Australia’ (Eds. S. Van Dyck and R. Strahan) pp. 654-656. (Reed New Holland: Sydney).