Powerful or Great Hawk Owl

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Image:Powerful.JPG

Common Name: Powerful or Great Hawk Owl
Scientific Name: Ninox strenua

Size: Males 19 - 25 ½ inches (48-65 cm) Wingspan: 45 - 53 inches (115-135 cm)

Habitat: Australia. This species occurs in open forest and woodlands in eastern Australia, from south-west Victoria to at least Eungella, and possibly Bowen, Queensland. Large areas of the species' range are now unsuitable as a result of clearing for agriculture and pastors, although the species now occupies suburban Brisbane, Sydney and Melbourne.

Found in typically wet and hilly sclerophyll forest with dense gullies adjacent to more open forest. Will also occur in smaller, drier forest, provided that there are some large tree hollows and an adequate supply of prey.

Status: Least Concern. Global population: 3,300 to 4,250. Although densities in remaining forest may eventually be affected by a reduction in the availability of suitable nest hollows and den sites as a result of intensive forestry practices, studies indicate birds persist in mosaics of unlogged forest, in which they nest, and logged forest, in which they forage. There was no difference in density between heavily logged, lightly logged and unlogged forest. Intense wildfire can result in local loss but, if suitable habitat remains nearby, they may return to forage. Poisoning, disturbance and predation by foxes may also cause nest failure and some mortality, but are unlikely to be significant. The Powerful Owl is listed as threatened on the Victorian Flora and Fauna Guarantee Act (1988) and listed as “Vulnerable” on the list of threatened vertebrate fauna in Victoria.

Diet: Slow-moving arboreal mammals and large birds. Most hunting is done at dusk and dawn from perches. Large prey is often not eaten until the night after capture and Owl roosts with one foot on prey which is draped over branch.

Nesting: Males are larger than females. Breeds during winter, with each female typically laying on almost the same date each year. Most eggs are laid from the second week in May to the third week June. Males begin calling in late February or early March. Around this time, pairs begin to roost closer together, at first in same tree and then on same branch, often still some distance from the potential nest site. The nest is a large hollow, nearly always in the trunk or broken off top of a big eucalypt. In tall forest this is usually at the head of a gully or on a hillside at heights from 20-45 meters (65.5-147.5 feet). Where tall trees are not available, the nest may be in open forest or among part-cleared timber at levels as low as 6 meters (19.5 feet). Usually 2 eggs, rarely 1, are laid at 4 day intervals. They are almost spherical and are dull white, measuring 49-56mm (1.9-2.2") by 43-46mm (1.7-1.8"). Incubation is about 38 days with the male rarely visiting the nest after laying - the female leaves the hollow to take food from him. The young have first and second downs of white, becoming stained in the nest. The Beak and feet seem disproportionately huge in early weeks. They are brooded constantly by the female until about 4 weeks when she abruptly ceases to brood by day and her visits become progressively shorter at night. First flight is at 7 to 8 weeks while still partially downy. After fledging, the young remain with their parents for weeks or months, roosting near or with one of them, sometimes remaining with parents in late autumn and this may inhibit them from breeding in the following season. Powerful Owls have always been thought to be shy and not aggressive at the nest but this needs considerable qualification. Females are certainly shy and may desert a nest after minimal human disturbance, particularly early in the season. Some males, however, may be extremely aggressive in the breeding season, attacking humans with great ferocity even at a considerable distance from the nest. This is most likely when there are young in the nest but may occur even before laying and occasionally when juveniles are roosting nearby.

Cool Facts: Lives permanently in pairs. Roosts by day singly, in pairs or in family groups of 3-4, in foliage or open tree in forest or woodland. They will often roost with the remains of prey clutched in their talons. May be easily approached during the day, but is shy and difficult to observe at night.

Found in Songbird ReMix Owls of the World Volume 1 and Songbird ReMix Australia Volume III

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