Thick-billed grasswren (eastern subspecies) (Amytornis textilis modestus) - critically endangered species listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Thick-billed Grasswren (eastern subspecies) Amytornis textilis modestus (North, 1902) as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act, and as a consequence, to omit reference to Amytornis textilis modestus (North, 1902) from Part 1 of Schedule 1 (Endangered species) of the Act. Listing of Critically Endangered species is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Thick-billed Grasswren (eastern subspecies) Amytornis textilis modestus (North, 1902) is a small (16 cm), furtive, terrestrial, rusty brown songbird with fine white streaks on the head and body, short wings, and a long cocked tail like a fairy-wren. It is similar to other grasswrens in NSW, but lacks the facial patterns of the paler Grey and Striated Grasswrens.

2. Amytornis textilis modestus is one of three subspecies of the Thick-billed Grasswren that occur in chenopod shublands in southern arid Australia. Subspecies  A. t. modestus (North, 1902) occurs in western NSW, north-east South Australia and southern Northern Territory,  A. t. myall (Mathews, 1916) in western South Australia, and  A. t. textilis (Dumont, 1824) of Western Australia (Higgins  et al. 2001). Subspecies  A. t. modestus formerly occurred on the lower Namoi River, and in the Mossgiel-Ivanhoe area north-west to at least Milparinka and the Grey Range (McAllan 2000; Higgins  et al. 2001). The population on the lower Namoi River may have been isolated, but range limits and connectivity between populations are uncertain and distribution was patchy. Western NSW populations may have been contiguous or near-contiguous with the isolated population of  A. t.  modestus near Yunta in adjoining South Australia ( e.g. Black and Baxter 2003). The second, and larger, population of  A. t.  modestus is widespread in north-east South Australia. Recent unpublished studies and genetic data are expected to elevate this subspecies to full species rank, as  Amytornis modestus (North 1902), when published in the near future (Black 2008).

3. The size of the population in NSW is uncertain, but presumed to be extremely low and in a very highly restricted area. There have been no records in NSW since 1936 (i.e. for more than 50 years) (Black and Longmore 2009). The species may qualify for listing as Presumed Extinct (in NSW), and is assumed so by most authors ( e.g. Garnett and Crowley 2000; Higgins  et al. 2001). However, McAllan (2000) speculated that it might still occur in the Grey Range, and that its habitat has recovered in Sturt National Park following reservation and the spread of the rabbit calicivirus. Furthermore, the species is cryptic and occurred in remote, arid, sparsely human-populated areas where sufficient targeted survey may yet detect it. The South Australian population of the Thick-billed Grasswren is estimated at 20 000 birds and its status there is considered ‘Least Concern’ ( sensu IUCN 2001), although some subpopulations have disappeared (Garnett and Crowley 2000).

4. A severe population reduction is inferred from the large contraction in geographic range. There have been no records on the lower Namoi since the species’ original discovery there. It was formerly common around Ivanhoe and Mossgiel, but disappeared from there by the early 1900s (Higgins et al. 2001). There have been no records from the Grey Range since its original discovery there in 1912, but there has been no targeted survey. The population is thought to have crashed in NSW following very high stocking rates and drought in the early decades of pastoral development (McAllan 1987). The Thick-billed Grasswrens habitat is inferred to be declining in quality based on historical changes in vegetation throughout the arid and semi-arid zone.

5. The main threat to the Thick-billed Grasswren is continued habitat destruction and degradation through overgrazing by livestock, rabbits and feral goats, compounded by drought. Other threats include predation by cats and foxes and the impacts of stochastic events such as wildfire. Inland bioregions within the species NSW range (Darling Riverine Plain, Riverina) are 33-40% cleared and moderately stressed, with a landscape stress factor 2-3 out of 6 (Barrett et al. 2007). Even little-cleared bioregions farther west are moderately stressed (Mulga Lands, Broken Hill Complex with a stress rating of 4; Channel Country with a stress rating of 3: Barrett  et al. 2007). ‘Competition and grazing by the feral European Rabbit,  Oryctolagus cuniculus (L.)’, ‘Competition and habitat degradation by feral goats,  Capra hircus Linnaeus, 1758’, ‘Predation by the feral cat,  Felis catus (Linnaeus, 1758)’, and ‘Predation by the European Red Fox,  Vulpes vulpes (Linnaeus, 1758)’ are listed as Key Threatening Processes under the NSW  Threatened Species Conservation Act 1995.

6. The Thick-billed Grasswren subspecies A. t. modestus and  A. t. myall are each nationally listed as Vulnerable on the  Environment Protection and Biodiversity Conservation Act 1999.

7. Thick-billed Grasswren (eastern subspecies) Amytornis textilis modestus (North, 1902) is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the  Threatened Species Conservation Regulation 2002:

Clause 17

The total number of mature individuals of the species is observed, estimated or inferred to be:

(a) extremely low.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 31/07/09
Exhibition period: 31/07/09 - 25/09/09

References:

Barrett GW, Silcocks AF, Cunningham R, Oliver DL, Weston MA, Baker J (2007) Comparison of atlas data to determine the conservation status of bird species in New South Wales, with an emphasis on woodland-dependent species. Australian Zoologist 34, 37-77.

Black A (2008) Recent observations of grasswrens. Birds SA Newsletter 206, 5.

Black AB, Baxter CI (2003) Observations of Thick-billed Grasswrens on the North Olary Plains. South Australian Ornithologist 34, 70-74.

Black AB, Longmore NW (2009) Notes on grasswren eggs in Len Harvey’s collection, Museum Victoria. Aust. Field Ornithology 26, in press

Garnett S, Crowley G (Eds) (2000) ‘The action plan for Australian birds 2000.’ (Environment Australia: Canberra)

Higgins PJ, Peter JM, Steele WK (Eds) (2001) ‘Handbook of Australian, New Zealand and Antarctic birds (Vol. 5).’ (Oxford University Press: Melbourne)

IUCN (2008) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 7.0.’ (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland)

McAllan IAW (1987) Early records of the Thick-billed Grasswren Amytornis textilis and Striated Grasswren  Amytornis striatus.  Australian Birds 21, 33-34.

McAllan IAW (2000) On some New South Wales records of the Grey Grasswren and the Thick-billed Grasswren. Australian Bird Watcher 18, 244-246.