The Australian boobook (Ninox boobook ), which is known in some regions as the mopoke, is a species of owl native to mainland Australia, southern New Guinea, the island of Timor, and the Sunda Islands. Described by John Latham in 1801, it was generally considered to be the same species as the morepork of New Zealand until 1999. Its name is derived from its two-tone boo-book call. Eight subspecies of the Australian boobook are recognized, with three further subspecies being reclassified as separate species in 2019 due to their distinctive calls and genetics.
The smallest owl on the Australian mainland, the Australian boobook is 27 to 36 cm (10.5 to 14 in) long, with predominantly dark-brown plumage with prominent pale spots. It has grey-green or yellow-green eyes. It is generally nocturnal, though is sometimes active at dawn and dusk, retiring to roost in secluded spots in the foliage of trees. The Australian boobook feeds on insects and small vertebrates, hunting by pouncing on them from tree perches. Breeding takes place from late winter to early summer, using tree hollows as nesting sites. The International Union for Conservation of Nature has assessed the Australian boobook as being of least concern on account of its large range and apparently stable population.
The smallest owl on the Australian mainland, the Australian boobook is 27 to 36 cm (10.5 to 14 in) long. The nominate subspecies is the largest. It has short, rounded wings and a short tail, with a compact silhouette in flight. Australian boobooks on the Australian mainland follow Bergmann's rule, in that birds from cooler and more southerly parts of the range tend to be larger. Thus, birds from the Canberra region weigh around 300 g (11 oz) while those from the Cape York Peninsula and Broome are around 200 g (7.1 oz). Females tend to be a little larger and heavier than males, with males weighing 146–360 g (5.1–12.7 oz) and females 170–298 g (6.0–10.5 oz).
The Australian boobook has generally dark brown head and upperparts, with white markings on the scapulars and spots on the wings. Its head lacks tufts common in other owls and has a paler facial disk, with a white supercilium (eyebrow) and dark brown ear coverts and cheeks. The brown feathers of the upper forehead, above the supercilium, and sides of the neck have yellow-brown highlights. The feathers of the lores, chin and throat are white with black shafts. The feathers of the underparts are mostly brown with white spots and dark blue-grey bases. The upper tail is dark brown with lighter brown bars and a grey fringe at the end, while the undertail is a lighter grey-brown. The female tends to be more prominently streaked than the male overall, though this is inconsistent and wide variation is seen. The eyes have been described as grey-green, green-yellow, or even light hazel. The bill is black with a pale blue-grey base and cere. The feet are greyish to pinkish brown with dark grey to blackish claws. The underparts are pale, ranging from buff to cream, and are streaked with brown. The overall colour is variable and does not appear to correspond to subspecies or region. In northern and central Australia, Mayr found that the colour of the plumage appears to correlate with the rainfall or humidity, paler birds being found in three disjunct areas, each around 1,600 kilometres (990 mi) away from the other two: the western Kimberley and Pilbara, Sedan on the Cloncurry River, and around Ooldea, with darker birds found on Cape York and Melville Island.
Young Australian boobooks are usually paler than adults and do not attain adult plumage properly until their third or fourth year. Juveniles (up to a year old) have whitish underparts and foreneck, a larger and more prominent pale eyebrow and larger whitish spots on their upperparts. The tips of their feathers are white and fluffy, remnants of the nestlings' down. These are worn away over time, persisting longest on the head. The feathers of the head, neck and underparts are fluffier overall. Immatures in their second and third year have plumage more like adults, though their crowns are paler and more heavily streaked.
The Australian boobook is found across mainland Australia, although it is scarce in more arid regions such as western New South Wales, southwestern and western Queensland, much of South Australia away from the coast and interior Western Australia and Northern Territory. In drier areas, it is generally found along watercourses such as the Darling and Paroo Rivers, and Lake Eyre Basin. It is found on numerous offshore islands such as Groote Eylandt, Melville Island, Mornington Island in the Gulf of Carpentaria and many islands off eastern Australia. It is found in southern New Guinea, Timor and surrounding islands in Indonesia. It is found in a wide range of habitats, from forest and open woodland to scrubland and semidesert areas. In Australia, it resides in mainly eucalypt forests. It has adapted to landscapes altered by human activity and is found in farmland and suburban areas as long as some scattered trees are present.
The Australian boobook is a mainly nocturnal species, though it may be active at dawn and dusk. It is heard much more commonly than seen, being particularly vocal in the breeding season. The characteristic two-note boo-book call or hoot can be heard up to 1 km (0.6 mi) away, the second note generally lower in pitch than the first. Calling takes place from sunset through dawn, generally with a peak in the two hours after dusk and just before dawn. It can continue for several hours. The male's hooting is higher pitched and of shorter duration, and is heard much more commonly than that of the female. He uses it as a contact call and to advertise his territory to females, as well as when bringing food to his mate or even before mating. Birds give a harsher version of the call when mobbing intruders. Both sexes, though mainly the female, give a single monosyllabic hoot as an alarm call or warning. Australian boobooks also make a repetitive croaking or grunting call while courting, mating, or greeting, or as a response to other boobooks hooting. Birds may switch from croaks to hoots seamlessly. Males generally croak at the beginning of the evening, and when arriving at the nest with food. A purring or braying call is used by both sexes as a contact call around the nest and (more quietly) when bringing food to nestlings, or by the female to beg for food from the male. The female makes a low trill during courtship and nesting. Growls, high-pitched yelps, and screeches can be made when attacking intruders.
The Australian boobook maintains and defends a territory in the breeding season; whether this continues for the rest of the year is unclear. It retires to densely foliated spots in trees in the daytime, each individual often having several roosting sites. Caves or ledges are alternative roosting sites if no suitable trees are available. Although unobtrusive, it may give itself away by droppings or pellets on the ground beneath. The Australian boobook is mobbed by passerines if discovered. It may allow people to approach to within 1 to 3 m (3.5 to 10 ft).
The maximum age recorded from banding has been 15 years 11 months, in a bird caught and later caught again on Black Mountain in the Australian Capital Territory.
The Australian boobook generally preys on mice, insects, particularly nocturnal beetles and moths, and birds the size of a house sparrow (Passer domesticus ). A higher proportion of its diet is invertebrates compared with other Australian owls. Fieldwork in the vicinity of Canberra found that vertebrates made up more of the diet in autumn and particularly in winter. Although more invertebrates were eaten than vertebrates (even more so in autumn), they made up only 2.8% of the biomass consumed. Mammals were the predominant prey species, especially the house mouse (Mus musculus ), and also black rat (Rattus rattus ), bush rat (R. fuscipes ), and Gould's wattled bat (Chalinolobus gouldii ). Birds including common starling (Sturnus vulgaris ), house sparrow, red-browed finch (Neochmia temporalis ), common myna (Acridotheres tristis ), red-rumped parrot (Psephotus haematonotus ), and white-browed babbler (Pomatostomus superciliosus ), and invertebrates including grasshoppers, crickets, beetles, cockroaches, moths, wolf spiders, and huntsman spiders were also consumed. A study in Victoria found that larger animals were eaten, including Baillon's crake (Porzana pusilla ), common ringtail possum (Pseudocheirus peregrinus ) and feral rabbit (Oryctolagus cuniculus ).
Using a fence, branch, or telegraph pole as a perch or vantage point from which to hunt, the Australian boobook pounces on prey then retreats to a tree or elevated place to eat it. It often hunts in open areas near trees, and also where prey is likely to congregate, such as mice near haystacks or barns, or flying insects near street- or house-lights.
Across Australia, breeding takes place from July to February, though peaks in October, and is generally earlier in more northern areas. Eggs are laid from August to October in Queensland, from September to November in New South Wales and southern Western Australia, July to September in central and northern Western Australia, in October and November in Victoria, and in September to December in South Australia.
The Australian boobook nests in holes in trees between 1 and 20 m (3–70 ft) above the ground. The holes are generally vertical, and mostly in eucalypts, though other trees such as coast banksia (Banksia integrifolia ) have been recorded. Some sites are reused by the species for up to 20 years, especially if broods have been successfully raised in them before. Boobooks may also evict other birds such as galahs (Eolophus roseicapillus ) to use their hollows, and have used sites abandoned by babblers, crows, and ravens. The male does more of the site preparation, such as lining the base of the hollow with leaves.
Two or three oval, white eggs, laid two to three days apart, are most commonly laid in a clutch, though one to five may be seen. They average 41.6 mm long by 35.5 mm wide and are finely pitted. The female alone incubates the eggs, during which time she is fed by the male. She does leave the nest at dusk for around half an hour, sometimes to bathe. Incubation takes 30–31 days, with the young often hatching at the same time. Occasionally, the time between the first and the last eggs hatching can be a few days.
Newly hatched chicks are covered with whitish down, and are blind and largely helpless (nidicolous). Their eyes begin to open on day 6 and are fully open by day 15. The juvenile feathers begin growing through the down from days 7 to 10, covering the baby owls by two weeks of age. Their mother broods them continuously for the first week, then only in the day until the third week. Her partner brings food to the nest, which she tears into pieces before feeding the nestlings. The young regurgitate pellets and defecate in the nest, which becomes quite smelly. They leave the nest 5–6 weeks after hatching, by which time they are fully feathered, with downy head and underparts and short tails. The tail reaches its adult length by 65 to 70 days. Young boobooks then live in their parents' territory for a further 2–4 months before dispersing, losing the remainder of their downy feathers by around 5 months of age.
Brushtail possums (Trichosurus spp.) and introduced cats and rats raid the nests for nestlings and eggs, and raptors such as the brown goshawk (Accipiter fasciatus ), grey goshawk (Accipiter novaehollandiae ), Australian masked owl (Tyto novaehollandiae ), and probably powerful owl (Ninox strenua ) seize young birds. Juvenile Australian boobooks are at greater risk after bushfires and have perished after being tangled up in dodder (Cassytha ) or bidgee-widgee (Acaena novae-zelandiae ).
A widespread and generally common species, the Australian boobook is listed as being a species of least concern by the International Union for Conservation of Nature, on account of its huge range and stable population, with no evidence of any significant decline. Like most species of owl, the Australian boobook is protected under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) meaning the international import and export of the species (including parts and derivatives) is regulated. A decline has occurred on the Swan Coastal Plain north of Perth. There, Australian boobook owls are dying after eating the rodents people have killed with second-generation anticoagulant rat poison. Older poisons such as warfarin or coumatetralyl were unlikely to affect owls.
