Byron Flora and Fauna Study 1999 - Byron Shire Council

A GREENPRINT FOR A SUSTAINABLE FUTURE
Powerful Owl Ninox strenua
Regional distribution and abundance. The Powerful Owl is widely but sparsely distributed throughout northeastern
NSW (ANSWW database), which is recognised as one of the species’ population strongholds (Scotts 1996). The highest
concentrations of records occur in the high elevation escarpment forests characterised by gentle topographic relief (NSW
National Parks and Wildlife Service 1994) such as in the Washpool-Gibraltar Range and Chaelundi areas, along the
eastern edge of the New England Tablelands, on the Dorrigo and Carrai Plateaus and in the Werrikimbe and Barrington
Tops areas (ANSWW database). It is uncommon to rare in coastal areas.
General ecology (habitat, shelter, diet, territory, breeding, movements). The Powerful Owl occurs primarily in eucalypt
forests and has a preference for large unfragmented patches containing mosaics of wet and dry sclerophyll forest (NSW
National Parks and Wildlife Service 1994). The species also occurs occasionally in rainforests and eucalypt woodlands.
It is associated with high densities of arboreal marsupials, particularly the Greater Glider and Common Ringtail Possum,
which are the main prey items (Kavanagh 1988, Hollands 1991, Debus and Chafer 1994). Other arboreal marsupials
such as the Sugar Glider and Yellow-bellied Glider are also taken, as are a range of large birds such as cockatoos and
currawongs and the Grey-headed Flying-fox Pteropus poliocephalus. A relatively open forest canopy appears to be favoured
for hunting (Traill 1993, Milledge 1994).
The territory size has been estimated at 800-1000 ha, although it may be more extensive in lower quality habitat, and
territories are spaced at distances of 5 to 20 km (Fleay 1968, Schodde and Mason 1980, Kavanagh 1988).
Roosts are usually in dense understorey or sub-canopy vegetation and often in the heads of gullies (Kavanagh and Bamkin
1995). During the breeding season the female roosts in the nest hollow and the male roosts in a vegetation patch within
200 m of the nest site.
The nest is selected in a spacious tree hollow in the main trunk or in a gently sloping hollow branch next to the trunk,
usually in a mature or senescent eucalypt or occasionally a rainforest tree (Schodde and Mason 1980, Hollands 1991).
The same nest site is often used a number of years in succession and one and sometimes two young are raised (Hollands
1991).
Movements of the Powerful Owl are poorly understood but some pairs appear to be sedentary within their extensive
territories while others, perhaps non-breeding individuals, undertake wider post-breeding dispersal.
Conservation status and threatening processes. The Powerful Owl is listed on Schedule 2 of the TSC Act, 1995 as
Vulnerable. The original reasons for its listing as an endangered species were ‘population suspected to be reduced;
distribution reduced; poor recovery potential; threatening processes moderate; ecological specialist’ (NSW Scientific
Committee).
The major threats to the species are intensive forest management practices which result in the losses of large hollowbearing
trees required for nest sites and the maintenance of high prey densities (Debus and Chafer 1994), and dense
understorey patches used for roosts. Frequent burning associated with grazing leases in State Forests also leads to the
accelerated collapse of senescent trees and the loss of dense understorey patches.
Other threats to the Powerful Owl include its sensitivity to human disturbance in the vicinity of the nest (Hollands 1991)
and the predation of recently fledged young by the Fox.
Local distribution and abundance. The relatively few records of the Powerful Owl in Byron Shire are mainly confined to
the extensive, elevated forest patches in the northwestern hinterland. Pairs appear to be resident in the Whian Whian
State Forest and Mt Jerusalem National Park-Nullum State Forest areas and their large home ranges probably include
private lands at the peripheries of these blocks. There are no documented breeding records in the Shire. Immatures or
non-breeding individuals may wander more widely, although the only confirmed coastal record is in the Anderson’s
Ridges area (Kinhill 1997). An unconfirmed record exist for the Broken Head area (Araucaria Community 1997).
Local ecology and conservation significance of the study area. The tracts of forest contained in the public lands in the
Shire’s north-west and contiguous forests on private lands appear to represent part of the home ranges of at least two
pairs of Powerful Owls resident in the Nightcap and Koonyum Ranges. The Nightcap and Koonyum Ranges are an
important refuge for the species in far northeastern NSW. Although breeding has not been reported, it is likely that it
occurs in these forests and they could provide colonists for rehabilitated areas elsewhere in the Shire as stands mature.
Conservation of the Powerful Owl in Byron Shire is likely to depend on the maintenance of high diversities and densities
of arboreal marsupials, which will in turn be dependent on retaining a substantial proportion of old-growth forest
elements in existing stands. In this regard, forest in Mt Jerusalem National Park, Inner Pocket Nature Reserve and
surrounding private lands assume particular significance for the species’ long term conservation.
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