Data Zone
Justification of Red List category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence under 20,000 km² combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (under 10,000 mature individuals with a continuing decline estimated to be over 10% in ten years or three generations, or with a specified population structure). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (over 30% decline over ten years or three generations). For these reasons the species is evaluated as Least Concern. The status of this species was recently reassessed against the IUCN Red List criteria at national level for the Action Plan for Australian Birds 2020 (Garnet and Baker 2021), and not found to approach or meet the thresholds for threatened status, thereby supporting its continuing treatment as globally Least Concern.
Population justification
Garnett and Crowley (2000) estimated the population size as follows: approximately 100,000 individuals of subspecies liredalei, approximately 10,000 individuals of subspecies rosinae and approximately 24,000 individuals of subspecies hedleyi, giving an overall total of 134,000 individuals. (Garnett and Crowley 2000). This population is suspected to be in decline owing to ongoing habitat destruction caused by over-grazing by introduced rabbits and sheep (Garnett and Crowley. 2000).
Trend justification
This population is suspected to be in decline owing to ongoing habitat destruction caused by over-grazing by introduced rabbits and sheep (Garnett and Crowley. 2000).
This species is endemic to South Australia and Western Australia, Australia. The nominate subspecies is widespread through the arid and semi-arid regions of both states. Although there has been a recent contraction in the east of its range, its extensive range outside the agricultural zone appears to be unaffected. Subspecies rosinae has a very restricted distribution, with three principle populations along the northern shore of the Gulf of St Vincent, from St Kilda to Ardrossan. Subspecies hedleyi has a fragmented distribution, primarily across Big and Little Deserts, Victoria, and Ninety Mile Plain, South Australia.
Much of the chenopod shrublands used by iredalei are degraded by grazing sheep and rabbits. However, a reduction in grazing on the Nullarbor of both sheep and rabbits may be allowing some recovery of habitat. Subspecies rosinae is threatened by recreational and industrial use of saltflats, and future coastal developments. Clearance for agriculture has affected hedleyi in South Australia, particularly in the 1980s, but has now largely ceased, though large-scale fires are frequent and may be affecting abundances. Its populations in the Big and Little Deserts appear fragmented despite large areas of protected, suitable habitat (Garnett and Crowley 2000).
Text account compilers
Rutherford, C.A.
Contributors
Garnett, S.
Recommended citation
BirdLife International (2024) Species factsheet: Slender-billed Thornbill Acanthiza iredalei. Downloaded from
https://datazone.birdlife.org/species/factsheet/slender-billed-thornbill-acanthiza-iredalei on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.