Brown Thornbill: Art of Survival in Dry Woods into the Wild
Family: Brown Thornbill (Acanthiza pusilla) belongs to the family Acanthizidae and is a member of the order Passeriformes and the genus Acanthiza.
Habitat: Brown thornbills can be found in rushes and bracken along rivers and streams, coastal dune thickets, shrublands, rainforests, and dry woods with high undergrowth, all at heights up to 1,200 m (3,900 ft). Ranging across much of southern Australia and the inland, Brown Thorn bills are sedentary birds in a variety of habitats, from rainforest to arid Mulga Acacia woodland. The thornbills are not spread evenly through their vegetation but occur in pockets, common to all of which are taller, close shrub layers one to five meters high. When not breeding, established pairs advertise with regular singing even when they are not holding territories of a quarter to five hectares there, though not as regularly. Young forage with their parents at family parties in the months after breeding but are expelled from the territory during autumn and early winter.
Identification: Both adult sexes are similar. The upper parts are generally rich olive-brown to brownish grey, according to race; the rump is more rufous-brown or rich russet in the grey race. The wings are dark grey-brown, with paler edges. The tail is dark grey-brown with a black subterminal band and grey-buff to white tips on the inner webs of all but the central pair of feathers. The face is flecked olive- to pale-grey, scalloped russet to white on the forehead. The underparts are cream to pure white, grading to olive-brown, grey, or yellowish on the flanks and undertail. The throat and breast are too heavily streaked grey-black. The eyes are red. The bill is black. The feet are dusky brown. The immature bird (as adults) is duller and more lightly streaked on the breast. The eyes are brown. The adult plumage is gained at the general body molt in the first autumn.
Life Span: Many wander into unusual habitats and most perish. Those who survive to find a territory of their own may live for 10 years or more.
Behavior: Day by day, Brown Thornbills spend most of the morning and afternoon foraging through the mid- and upper strata of their shrubberies, infrequently coming close to the ground. They hop glean briskly among foliage and along twigs, working through one bush before flitting jerkily to the next. Outside the breeding season, Brown Thornbills join mixed feeding flocks of other species, particularly White-browed Scrubwrens, buff-rumped thornbills, and striated thornbills, within the vicinity of their territories. Only the female builds and incubates, but the male commonly sings nearby in territorial defense. Then, in excitement, the birds will cock and flush their tails like wrens, particularly the inland race. Both Horsfield’s and Golden Bronze Cuckoos and, occasionally, Fantailed Cuckoos parasitize them.
Vocalizations: The beautiful Brown Thornbill produces a greater variety of calls than any other thornbill, even though they never dominate the sounds of the bush. The grey broad-tailed race inland is particularly varied in its voice, whistling and chipping in contact, churring harshly in alarm, and giving protracted trills and whistles in song, with perhaps occasional mimicry.
Brown thornbill call is soft chips and a plaintive whistle; seee (inland race only) in contact; harsh staccato buzzing and churring in alarm. The song consists of a series of whistled twitterings, ending in a short swirled metallic trill; mimicry is often interwoven and more varied and protracted in the inland grey race. When a raptor is coming, the adult bird can imitate other birds’ alarm calls, such as the New Holland honeyeater’s, to warn other predators—including pied currawongs—against attacking their nests.
Diet: The primary food source is insects. The bird consumes grasshoppers, ants, spiders, beetles, and lerps. Insects, and occasionally seeds, are picked from leaves, under bark, and sometimes from the ground. The birds also take advantage of flowers, such as those on the spikes of grass trees (Xanthorrhoea). Working its way up a spike, each bird inserts its bill into each flower and holds it there for several seconds, probably taking nectar.
Nesting and Breeding: Brown thornbill nesting and breeding occur in June–December; in colder areas, they start as late as September. Nestle in an untidy dome with a slightly hooded side entrance near the top. The nest is made of shreds of bark, coarse grasses, and ferns bound with a little cobweb. Also, the nest is lined with finer grasses, fur, and feathers; built-in low branches, shrubberies, fern thickets, or under tussocks on the edge of banks.
Eggs: The bird lays two, usually three eggs; white to pale flesh, liberally speckled and blotched with red-brown, mostly at the large end; oblong-oval, about 16 x 12 mm. The incubation period is about 18–21 days for females. The young fledge in about 14–15 days.
Distribution: Brown thornbill is found in shrubberies, from under rainforest to arid zone woodland, throughout the southern and inland mainland north to 20°S, and also Tasmania and other offshore islands.
Races: There are seven races: five olive-brown with russet frons scalloping around the coastal mainland, King Island, and Tasmania. Also, one grey with white frons scalloping throughout the inland and southern Mallee; one intermediate on Kangaroo Island, South Australia. Often regarded as a separate species, the greyer ‘Inland’ or ‘Broad-tailed’ thornbill of the arid zone is now treated as a race of the Brown.
First to propose this were the ornithologists Ernst Mayr and D.L. Serventy in 1938, partly because olive-toned Brown Thornbill-like birds with russet scalloping on the forehead in extreme southwestern Australia intergraded there with greyer, russet-rumped birds of the inland type, with white scalloping on the frons.
Mayr and Serventy’s suggestion was not followed at the time because it was thought that the two forms did not intergrade where they met in the east. Recently, it has been found that they do, wherever they come into contact along the western watersheds of the Great Dividing Range: at Tenterfield, Cobbora, and Temora, New South Wales; in the Big Desert, Victoria; and in the upper South-East and Adelaide Plains, South Australia.
Alternative Names: The bird has several other names and is known as Inland Thornbill, Broad-tailed Thornbill, Red-rumped Thornhill, Whitlock’s Thornhill, Brown Tit, Whitlock’s Tit, Tanami Tit, Whitescaled Tit, Lake Way Tit, Brownrumped Tit, Browntail, Scrub Thornhill, and Tit-bat.
Size: The brown thornbill measures about 100–110 mm in length, it is relatively small, and typically weighs 7 grams.
Status: The population is widespread, hence classified as least concern on the list of IUCN.