Weebill

The weebill (Smicrornis brevirostris) is a species of bird in the family Acanthizidae. It is an insectivorous passerine that is found throughout mainland Australia. At 8 to 9 cm (3.1 to 3.5 in) long, it is Australia's smallest bird. It was originally described by John Gould in 1838, and four subspecies are recognised. The weebill's plumage is nondescript, with olive-grey upperparts and paler, more yellowish underparts. It grades from more brownish plumage in the southern regions of Australia to more yellow in tropical areas.

The weebill is Australia's smallest bird at approximately 8 to 9 cm (3.1 to 3.5 in) long and weighing an average of 6 grams (adult bird). Wingspan is approximately 15 cm (5.9 in).

Weebills have inconspicuously coloured plumage ranging from yellowish-grey (front) to olive-brownish-grey (back). The two main feather pigments involved in this variation are yellow (phaeomelanin) and olive-brown (eumelanin). There is geographical variation in plumage across the four subspecies.

Adults have pale yellow eyes and a faint cream coloured supercilium. The throat feathers are grey, often with striation, and the flight feathers on the wings are pale brown. The tail feathers are brown with a black bar and white spot on the tip of all the rectrices, except the central pairs, which are completely dark. Both sexes are monomorphic in plumage colouration.

The bill is short and pale grey. The stubby bill of the weebill assists in distinguishing it from thornbills. The legs and feet of the weebill are grey, and like all passerines, their toe arrangement is anisodactyl for perching.

Juveniles have a similar plumage to adults, but can be identified by a brighter, yellow bill and greyer eye.

Four subspecies of weebill are currently recognised and exhibit slight variation in feather pigmentation, dependent on distribution. In the south and east of Australia, subspecies occidentalis and brevirostris are light brown; in the southwest, the subspecies occidentalis exhibits greyer plumage; while subspecies flavescens in northern and inland Australia is paler and more yellow. Additionally, the Northern Australian weebills are smaller than those in the south.

The voice of the weebill is a loud, clear, musical pee-pee p'wee, wee bit or wee willy weetee, often heard from a considerable distance.