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Threatened Species of the Northern Territory

SLENDER-BILLED THORNBILL (western subspecies) Acanthiza iredalei iradalei

Conservation status : Vulnerable Northern Territory: Extinct

Photo: G. Chapman

Description The slender-billed thornbill is a small bird, with head and body length of 9-10 cm. The upperparts are light olive-grey to dark olive-brown. The rump and base of tail are buff-yellow to yellow-olive. The forehead and cheeks are scalloped and flecked pale to deep cream. The underparts are uniformly cream-white to cream-buff. The bill is dark and the eye pale.

Distribution The slender-billed thornbill is endemic to Australia and occurs as three subspecies Known locations of the slender-billed thornbill across the semi-arid of the southern half of the from the Carnarvon Conservation reserves where reported: bioregion in to the South None. Australia- border. Only one subspecies has been recorded for the Ecology Northern Territory (NT). The slender-billed thornbill occurs in In the NT, the slender-billed thornbill is shrubland, typically in areas of saltmarsh known from a single specimen collected by S. dominated by samphire, bluebush (Maireana) A. White on the lower on or saltbush (Atriplex) around salt lakes or low Idracowra Station on 21 1913 (Storr heath on sandplain (Schodde and Tidemann 1977). There have been no records of the 1986; Schodde and Mason 1999). It feeds on species in the NT since this time. A potential invertebrates, mostly insects and spiders, that sighting from Barrow Creek in 1942 was it captures amongst the foliage of shrubs. It assessed as “…too doubtful to be considered rarely feeds on the ground despite the further” (Parker 1971). openness of its foraging habitat.

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The species is usually seen in pairs or small lower risk, least concern. No threatening flocks of 8-10 birds. The breeding runs processes have been positively identified. from July to November. Pairs form between Habitat degradation as a result of grazing by August-October and a small domed nest, sheep and rabbits is a potential threat in some constructed of grasses, bark strips and parts of its range cobwebs, with a side entrance is built in a low shrub. Up to three eggs are laid. Conservation objectives and management Conservation assessment The slender-billed thornbill is unlikely to still There is no existing management program for occur in the NT. It is known from only one this species in the NT. Any reliable potential record on Idracowra Station and that was in sightings of the species should be followed-up as soon as possible. 1913. The original label notes from the specimen indicate the species was “plentiful” Compiled by at that time (Parker 1971). The Idracowra locality was searched by Shane Parker and Chris Pavey David Howe during May 1970 without Simon Ward success, although Parker (1971) noted that [updated December 2012] extensive areas of suitable habitat occur in References the vicinity. Surveys in 2001 of the Finke bioregion, including Idracowra Station, did not Garnett, S.T., and Crowley, G.M. (2000). The find any evidence of the species (Pavey and Action Plan for Australian Birds, 2000. Joseph 2004). Therefore, the western (Environment Australia, .) subspecies of the slender-billed thornbill is Parker, S.A. (1971). Critical notes on the classified as in the NT. However, Extinct status of some central Australian birds. given the amount of suitable habitat Emu 71, 99-102. remaining in the southern NT, it is puzzling that the species has been located at only one Pavey, C. R., and Joseph, L. (2004). The site. In 2003, the specimen from Idracowra occurrence of the slender-billed thornbill Station (now housed in the American Museum Acanthiza iredalei in the Northern of Natural History, New York) was re- Territory. South Australian Ornithologist examined and found to have been correctly 34, 170-175. identified (Pavey and Joseph 2004). Therefore, the slender-billed thornbill is the Schodde, R., and Mason, I.J. (1999). The only bird species considered to have become directory of Australian birds: passerines. extinct in the NT since European settlement. (CSIRO Publishing, .) Schodde, R., and Tidemann, S.C. (eds) (1986). Threatening Processes Reader’s Digest Complete Book of The western subspecies of the slender-billed Australian Birds. 2nd edition. (Reader’s thornbill, to which the NT record belongs, Digest, .) occupies a 400 000 km2 area of southern Australia and has an estimated breeding Storr, G.M. (1977). Birds of the Northern population of 100 000 (Garnett and Crowley Territory. (Western Australian Museum, 2000). Indeed, Garnett and Crowley ). suggested that the subspecies should have a status of

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