The mountain thornbill (Acanthiza katherina) is endemic to Australia and is a member of the family Acanthizidae. A montane rainforest in northeastern Queensland is its habitat. This species is the link between Australian brown thornbills and New Guinea’s only thornbill. In the cloud forests of that island, there is also a Mountain thornbill with cream-colored eyes. A small warbler-like bird lives in the canopy of the rainforest’s mid- and upper levels.
Usually, in small groups of two to eight or more, it hops briskly among the branches at a height of five to twenty-five meters. This bird feeds on foliage and twigs, darting between trees in short, undulating dashes. Throughout their movements, the birds keep in constant communication by twittering.
There is an altitude range of 400 to 1200 meters. Lower hills are occupied by Mountain Thornhills and Brown Gerygones, two small foliage-gleaning insects. Most of the time, it resides in the upper strata of the forest, above 15 meters. It is unclear whether this has anything to do with their polymorphic plumage changes.
A Mountain Thornbill at a lower elevation tends to be brighter green above and yellower below than one at a higher elevation. Mountain Thornbills measure about 100–110 mm in length. There is no difference between the sexes as adults. The upper parts are green-olive, the lower back is brighter, and the upper tail coverts are tawny. Tail feathers are grey-brown, with white inner webs and dusky outer feathers.
Grey-brown wing quills with green-olive edges. Buff scallops on the forehead. The chin, throat, and upper breast are cream, and they are lightly scaled with grey; the sides of the face are cream-grey, and the rest of the underparts are cream-washed lemon. The eyes are white to cream in color. Black is the color of the bill. Grey-brown is the color of the feet. The immature bird is as dull as an adult.
Brown Thornbill’s voice is similar to Mountain Thornhill’s. An alarm buzzes chaah, chaaah, chaaah as single chips make contact. In contrast, Mountain Thornhill’s song is composed of sweet, short metallic trills, often preceded by several short, falling whistles.
September, December, and January are the nesting and breeding seasons. Grass and tendrils are interwoven into a bulky dome with a hooded side entrance. Nests are covered with green moss, lined with finer material, and slung from leafy branchlets or under banks 5–15 m above ground.
Two pinkish-white eggs, often spotted and blotched with brown, red-brown, and underlying grey, are laid by the bird. Approximately 17 x 12 mm in size, the eggs are oval-shaped. Between Cooktown and Paluma Range, QLD, it is found in mountain rainforests above 350 meters.
