Australian boobook

The Australian boobook (Ninox boobook), 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 sometimes it is 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 km (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.

On mainland Australia, it could be confused with the barking owl or the brown boobook (Ninox scutulata), a rare vagrant to the northwest, although the Australian boobook is easily distinguished by its squat posture and distinctive pale border to its face mask. The Tasmanian boobook has been recorded from southern Victoria, with one record from New South Wales. It has darker and more reddish upperparts with brighter white dots, with more prominent white dots and a yellow-brown tinge to the underparts. It has pinkish grey feet and golden eyes.