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SOUTHERN BOOBOOK OWL

Ninox  novaehollandiae

(other names Spotted Owl, Mopoke)

Image by Sharon McGrigor

Importance of tree hollows

By Danielle Davis


The diminutive little Southern Boobook is a nocturnal raptor (bird of prey) and the smallest and most abundant of our Australian owls. The name boobook comes from the Eora Aboriginal tribe, who were the original inhabitants of the Sydney region. It is also known as the "mopoke", due to its distinctive call which sounds like 'mo-poke'. They are part of the Ninox or ‘hawk owl’ group of owls due to the shape of their face and beak, being ‘hawk like’ in appearance, as opposed to the Tyto or ‘heart like shaped’ face group of owls, such as the Barn Owl, Grass Owl, Sooty and Masked Owl.

The Southern Boobook can live in most types of country ranging from dense forest to desert but are mainly found in wooded habitats throughout mainland Australia and Tasmania, and on some coastal islands. They are also often seen in towns and suburbs with abundant trees. Closely related species are found in New Zealand, New Guinea and Indonesia. If not seen, however the chief evidence of their presence is their characteristic call but with a good eye they can be spotted roosting through the daylight hours singly in tree hollows or dense foliage.
A mere 25 – 36 cm  long, with the female being slightly larger, they are identified by their plumage, which is dark chocolate-brown above and rufous-brown below, heavily streaked and spotted with white. The bill is grey with a darker tip, and the feet are grey or yellow (3 toes forward, 1 toe backward each with a strong talon claw). The facial disc is chocolate brown and the eyes are huge and yellow. Cape York birds in the far north are larger and have a darker brown colour where as Tasmanian birds are smaller and are more heavily spotted with white. Immature juveniles are almost entirely buff-white below, with conspicuous dark brown facial discs. Chicks are covered in thick white-downy feathers with powder blue eyes.
The call for birds of both sexes is often observed while they perched on an open branch or tree-top, emitting a distinctive 'boo-book' or 'mo-poke' through closed beak which can carry for a kilometer or more. Also low ‘trilling’ calls for contact and screams in aggression. Immature birds beg with whistling cricket-like trill.
Their diet, comprising of mainly insects & invertebrates(which they eat more of than any other owl), small mammals (such as the House Mouse Mus musculus), birds, frogs, and lizards.

Nnocturnal like all owls, although on dull days they will hunt crepuscularly, it is superbly adapted for night time and stealth hunting. Its soft leading edge feathers are so effective at eliminating noise, allowing it to swoop and hunt unsuspecting prey, that they have almost near silent flight. Most prey is detected by listening and watching from a suitable tall perch. Once detected, flying prey, such as moths and small bats, are seized in mid-air, while ground-dwelling preys are pounced upon. Although their main hunting technique is perch and pounce, they are agile birds with swift wing action and the ability to maneuver rapidly when pursuing prey or hawking for insects.

Owls, like many nocturnal animals, have very good night vision, but rely also on their excellent hearing - up to four times better than any other animal tested - which allows some to hunt in complete darkness. Because their left and right ears are placed at different levels on their heads there is a slight difference in the time taken for a particular sound to reach each ear. This time-lag enables the owl to pinpoint the source of the sound more accurately. The higher ear has an opening facing downwards and is more sensitive to sounds from below. Feathers within the characteristic facial disc are positioned so as to funnel sound to the ears. Stiff feathers bordering the ear slits are attached to moveable flaps so an owl can change the shape of its ear opening and focus its hearing. 

 

When swooping on its prey one of the owl's outer toes can be brought around so the four talons grip from four different directions. Large amounts of indigestible fur, feathers and bones are swallowed but once or twice a day these items are regurgitated, in tightly-packed pellets. Researchers can often learn a lot about animals living in a particular area by examining these pellets; bones of the rarely-trapped prehensile-tailed rat are the only indication that it is more common than sightings would suggest.
In addition to their excellent hearing, owls have, like other birds of prey, much better vision than humans. The owl's eye is packed with rod cells which are sensitive to low light levels and its large pupil means that an image is about two and a half times brighter to an owl than to a human. Hawk owls, such as the Boobook Owl, have incomplete facial discs and very large eyes, and so have relatively better night vision than hearing (Compared to the heart/disc shape faced owls). They hunt by perching, looking and diving, then carrying their prey in their talons and tearing it up before eating.

Because insects form a large part of its diet, nesting begins in spring which can be any where from August till February, although most activity occurs during October. As breeding time approaches, pairs of boobook's establish their nesting territory with much territorial hooting, particularly after dusk and before dawn. Like other Ninox owls, each mated pair courts side by side on a perch, bubbling, purring, nibbling and preening one another. The nest, normally built by the male and attended to by the female, is a living or dead tree hollow 3 – 25 m above the ground, which is usually sparsely lined with wood shavings, leaves and small twigs, but may be left bare as well. It should always be remembered that dead trees are as important as live ones, as they are the home for a wide range of mammals and birds. Once cleared, it may take hundreds of years for a tree to form such hollows.


 Having only one brood per season the female lays 2 – 5 (usually 2-3) round pale white eggs at 2 – 3 nightly intervals. She alone incubates the eggs for 26 – 33 days being fed by her mate, but after the chicks have hatched both sexes, and sometimes a second female helper, will feed the young birds, who are born altricial and are completely dependant on their parents. The baby birds stay in the nest until they are five or six weeks old when they fledge and leave the nest but will remain with their parents being fed for another 2 – 3 months when they are ready to hunt on the own.
There are twenty four diurnal raptor and ten owl species native to Australia.  Whilst owls are not taxonomically classed with the diurnal raptors, or birds of prey, they share many of the physiological characteristics, requirements and traits of diurnal raptors.  They have hooked bills, are carnivorous and, most significantly, use their powerful feet to catch and kill their prey.  They fill an equivalent niche in the environment, and for all practical intents and purposes may be considered "raptorial" by nature.

Images by Melanie Barsony & Alicia Carter

Reference:

Reader's Digest Complete Book of Aust. Birds

www.wildlifeaustralia.com

www.amonline.net.au

www.birdsinbackyards.net

 

Updated March 18, 2017  

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