Chestnut-rumped Thornbill

The Chestnut-rumped Thornbill (Acanthiza uropygialis) is a small, unassuming passerine bird, a member of the Acanthizidae family. It is distinguished by its pale-chestnut rump, a feature that has inspired its scientific name from the mediaeval Latin 'uropygium', meaning the rump. This bird is a plain, pale thornbill with pale eyes, and it exhibits no sexual dimorphism nor seasonal variation in plumage.

Identification Tips

Adult Chestnut-rumped Thornbills measure approximately 9.8 cm in length, with a wingspan of about 15.5 cm, and weigh around 6 grams. They possess a pale grey-brown upper body, a rich chestnut rump, and a mostly black tail with pale tips. Their ear-coverts are mottled, and there is a rufous suffusion on the forehead and crown. The underbody is plain whitish. Juveniles are similar to adults but plainer, with a duller head pattern and pale buff tail tips.

Habitat

These birds inhabit dry woodlands and shrublands, particularly favoring mulga and mallee eucalypts. They can also be found in thickets, saltbush, bluebush, lignum, and open pastoral country. Their range extends across arid and semi-arid zones to temperate and subtropical regions.

Distribution

The Chestnut-rumped Thornbill is endemic to mainland Australia, with its presence widespread throughout inland areas, west of the Great Dividing Range to the West Australian coast. However, it is notably absent in the far north and humid southwest of Western Australia.

Behaviour

Chestnut-rumped Thornbills are gregarious and typically seen in small flocks, pairs, or trios. They are active and restless, foraging in shrubs and trees, flitting and hopping in foliage and low branches. Their flight is characterized by low undulating dashes from cover to cover.

Song & Calls

The voice of the Chestnut-rumped Thornbill is penetrating, with a far-carrying song composed of similar phrases. This bird is also known to mimic the calls of other bird species.

Breeding

Breeding typically involves pairs, but there are instances of cooperative breeding. Nests are small, neat, and domed, constructed from dried grass, bark strips, and other materials, and lined with feathers, wool, or fur. The breeding season spans from June to December, with the potential for multiple broods.

Similar Species

The Chestnut-rumped Thornbill can be confused with other thornbills that have a rufous-brown rump patch, such as the Brown Thornbill (A. pusilla), Inland Thornbill (A. apicalis), and Slaty-backed Thornbills (A. robustirostris).

Diet and Feeding

Primarily insectivorous, the Chestnut-rumped Thornbill also occasionally consumes seeds. They forage by gleaning from leaves, twigs, branches, and the ground, as well as by probing into bark. They are often seen feeding in mixed-species flocks.

Conservation Status

The Chestnut-rumped Thornbill is classified as Least Concern by the IUCN. Despite a decreasing population trend, the species does not meet the thresholds for a more threatened category. However, it is listed among declining woodland birds, with habitat loss and degradation being potential threats to its population.