Australian Warblers: Acanthizidae
AUSTRALIAN WARBLERS: AcanthizidaeYELLOW-RUMPED THORNBILL (Acanthiza chrysorrhoa): SPECIES ACCOUNTS
YELLOWHEAD (Mohua ochrocephala): SPECIES ACCOUNTS
Australian warblers tend to be small- to medium-sized birds, with an average length of 3.5 to 10 inches (9 to 27 centimeters) and a weight range of 0.25 to 2.5 ounces (7 to 70 grams). Most of the species are olive-green, somewhat drab-colored birds, but with distinctive markings on the head and face, such as light eyebrows, spots, and streaks. Some species have yellow or reddish rumps. Some of the thornbills and gerygones have yellow undersides, while the pilotbird and rockwarbler have reddish brown underside. This family of birds has slender bills. The tails of some species are cocked, tilted, regularly. Males and females are similar in appearance.
Australian warblers occur in many different habitats throughout their distribution area including, mangroves, rainforests, eucalyptus (yoo-kah-LIP-tus) forests and woodlands, shrub lands, and desert.
Most of this family captures small invertebrates, animals without backbones, from the foliage, twigs, branches, and trunks, picking their prey with their long and slender bills. They eat primarily small insects, but occasionally some species eat seeds and fruits.
BEHAVIOR AND REPRODUCTION
The Australian warbler family of birds is a very active group, hopping over the ground and through the foliage of the trees or bushes. Some species can be very mysterious in their behavior. Most species tend to be sedentary and tend to stay in the same area throughout the year with only local movement. However, one species, the white-throated gerygone does migrate into southeastern Australia in the spring. All other species are weak fliers. In song and vocalization, most species are melodious, loud, and have distinctive voices. Some are even gifted mimics, able to copy or imitate other species' calls. Others have only buzzing, trilling or rattling notes with short quiet songs. Certain species like the bristlebirds have whistling calls that are carried far in order to announce their presence.
Some species are cooperative breeders, where nonbreeding birds assist the parents with the care and protection of chicks, while in other species only parents raise their chicks. The breeding season lasts from late winter to early summer. Several breeding attempts occur each season. Nests are domed, usually placed in trees or shrubs, with some in crevices and hollows, or even on the ground. Clutches commonly include two eggs, but have been observed with as many as five. The color of the eggs comes in many forms including white, white with sparse spotting, cream or buff with widespread spotting, and chocolate. The eggs that are incubated only by the female are laid at forty-eight-hour intervals. Incubation and the independence of fledglings are both accomplished over a long period of time. Both parents, and sometimes the helpers, feed the young. Many nests succumb to predators. Bronze-cuckoos lay their eggs in some nests and kick out the young warblers. Adult survival each year is as high as 80 percent—a high percentage for birds that are so small.
AUSTRALIAN WARBLERS AND PEOPLE
Humans do not often take notice of this small, drab bird, though the songs of some species are definitely well-known. With many exhibiting such cryptic behavior, bird watching can be difficult, which is one reason that it has taken so long to identify so many of the species.
One species of gerygone, the Lord Howe gerygone was already Extinct, no longer existing, by the beginning of the twenty-first century. The Biak gerygone is Endangered, facing a very high risk of extinction in the wild; and the Norfolk Island gerygone is Vulnerable, facing a high risk of extinction in the wild. These populations have been hurt by habitat loss as well as from the introduction of predatory mammals. In 2000, the Action Plan for Australian Birds listed a large number of this family as Threatened, in danger of extinction, or Almost Threatened, close to becoming threatened. Other threats to these populations have been extensive fires and grazing from the introduced mammals. Only the Coorong subspecies remained categorized as secure on the Australian list.
Physical characteristics: Yellow-rumped thornbills average 4 inches (10 centimeters) in length, with a weight of 0.32 ounces (9 grams). They are known for their bright yellow rump—from which they derived their common name—and their black crown with white spots, and white brow.
Geographic range: Yellow-rumped thornbills can be found throughout central and southern Australia, including Tasmania, an island off the southern coast of Australia.
Habitat: Yellow-rumped thornbills inhabit open woodland areas and edges, farmland, grassland that has trees or bushes sparsely located throughout the area, parks, and gardens.
Diet: Yellow-rumped thornbills are omnivores, eating both animals and plants. They eat primarily insects and other invertebrates, and occasionally, seeds. The birds forage the ground for the most part, but will sometimes forage on shrubs and low trees.
Behavior and reproduction: Yellow-rumped thornbills live in family groups or small flocks with others thornbills. They tend to be active, noisy, and sing with twittering melodies and calls. Their yellow rumps are easy to spot while in flight but they virtually disappear when the birds land. Generally they only move locally, and tend to be non-migratory, sedentary.
The breeding season is from July to December, and sometimes goes later. The nest is domed, built in a bush or sapling, and is made of grass, lichen, and other plant fibers. The side entrance is concealed by a hood. A false cup-shaped nest is put on the top, probably to confuse predators or cuckoos. Both males and females build the nest. Each clutch has two to four lightly speckled, pink eggs. Only the female incubates the eggs, which is a period of eighteen to twenty days. The fledging period lasts seventeen to nineteen days. The parents often have the assistance of helpers. Many nests do not survive predators or the parasites of the bronze-cuckoos.
Yellow-rumped thornbills and people: People are well-acquainted with this colorful bird, and it is particularly familiar to those who live in the country.
Conservation status: This species is not threatened with extinction. ∎
Physical characteristics: Yellowheads measure 6 inches (15 centimeters) in length, and weigh 0.7 ounces (20 grams). Their uppersides are olive with a bright yellow head and yellow breast.
Habitat: Yellowheads inhabit forest areas, especially those that are dominated by beech trees.
Diet: Yellowheads forage throughout the day in the shaded canopy, the upper layer of the forest, or upper subcanopy, layer just below the canopy. They are primarily insectivores, insect eaters, picking insects from the foliage, branches, and trunks, and sometimes even dead wood. Yellowheads prefer larvae, the newly hatched, wingless forms of insects. They sometimes eat fruit, flowers, and fungi.
Behavior and reproduction: During the non-breeding season, yellowheads form large flocks, and are joined by other bird species. During the breeding season, yellowheads live in pairs or trios and are distributed over a large home range. Their mechanical-like call is varied, with six to eight notes repeated rapidly.
The yellowhead engages in cooperative breeding, and is possibly polygamous (puh-LIH-guh-mus), having more than one mate. They breed from October to February. They build cup-shaped nests in holes. Clutch sizes are typically three to four eggs that are pinkish with reddish brown blotches. They are incubated only by the female for a period of eighteen to twenty-one days. The young fledge at twenty-one days. Two or three adults continue to feed them after fledging for up to fifty-five more days.
Yellowheads and people: There is no known significance between people and yellowheads.
Conservation status: Yellowheads have been declared Vulnerable. Their population has declined significantly due to loss of forest, and their habit of avoiding edges, stunted, and regrowth forests. They are not as vulnerable to nest predators as many New Zealand birds because they nest in holes, but the young birds that are newly fledged often face risk from predators. ∎
FOR MORE INFORMATION
Campbell, Brude, and Elizabeth Lack, eds. A Dictionary of Birds. Vermillion, SD: Buteo Books, 1985.
Higgins, P. J., and J. M. Peter, eds. Handbook of Australian, New Zealand & Antarctic Birds. Vol. 6, Pardalotes to Shrike-Thrushes. Melbourne: Oxford, 2002.
Hvass, Hans. Birds of the World, in Color. New York: E. P. Dutton & Company, Inc., 1964.
Simpson, Ken, and Nicolas Day. The Birds of Australia, A Book of Identification. Dover, NH: Tanager Books, 1984.
"Australo-Papuan Warblers, Acanthizidae." Bird Families of the World. http://www.montereybay.com/creagrus/auz_warblers.html (accessed on June 17, 2004).