A rare animal that appears to be common

The Powerful Owl (Ninox strenua) is a large nocturnal predator of forest country which feeds principally on possums and gliders.  Pairs will create nests in hollows of mature or dead trees to raise two or three chicks which take two years or more to reach maturity.  They are found throughout Victoria in areas where the rainfall exceeds 600 mm a year and where there is existing forest vegetation - there are no records on the south-western volcanic plains or the treeless areas of South Gippsland.  The Powerful Owl is classified as vulnerable in Victoria, it is listed under the Flora and Fauna Guarantee Act (FFG) and is classified as Least Concern in the IUCN Red Book.

The distribution map below shows the geographic range of the Powerful Owl to be about half of the state.  Most of the records are recent and many of them represent at least potentially breeding pairs.  This range, and the total number of recorded sightings, is similar to that for other forest birds such as the Australian King Parrot and the Crescent Honeyeater, species for which there is no conservation rating.  Why then is the Powerful Owl considered to be threatened when the others aren't?

There are several answers to this question, not all of which are related to each other, but most stem from the fact that Powerful Owls are large birds of prey that feed on possums. 

Animals that feed on other animals generally need larger areas to service their diet than those that feed on plants.  If the predator is big and needs warm-blooded prey, then its requirement for a home range will be considerably greater than that for a small species that feeds on insects.  This means that while the map showing the geographic range of the Powerful Owl could represent two thousand animals or less, the very similar map for the Crescent Honeyeater might represent 10-20 times that number of individuals.  The fact that there are almost as many individual records for the Powerful Owl as Crescent Honeyeater across this range is more a reflection of the huge survey effort that has been put into finding the relatively elusive nocturnal species rather than an indication of a true similarity in abundance.  Indeed it is probable that most of the records for Powerful Owls in any locality will represent multiple sightings of one or two birds.  For example, there are 68 records, over a five year period, listed for Powerful Owls in a 100 ha area of the Yellingbo Wildlife Reserve, about 50 km east of Melbourne.  Given that the owls live for a decade or more and normally need a home range in excess of 1000 ha, the likelihood that these records represent more than an single breeding pair, and perhaps offspring, is very low.

Large birds of prey tend to be more sedentary than smaller insectivorous and herbivorous birds who are often periodically nomadic when food becomes scarce. Once a pair of Powerful Owls establish a home range they will usually hold on to it for many years, which means that they must get everything they need from that area.  A limiting factor to owl breeding is the availability of tree hollows in which to nest.  The hollows need to be large to accommodate an adult and at least two chicks, and these are usually only found in trees that are 120 years old or more.  Unsurprisingly, timber harvesting has been cited many times as a major threat to Powerful Owls because of the reduction of mature trees and hence tree hollows.  Some biologists have argued that if a few mature trees are left in a forest logging coup then that should cover the breeding requirements for the small number of owls that live there.  This argument is offset, however, by the fact that many of the owl's prey are arboreal species that also require hollows for shelter and breeding.  Whatever the specific arguments, there can be little doubt that timber harvesting is an activity that is present almost throughout the range of the Powerful Owl and it is one of the primary reasons that the vulnerable classification has been assigned.

The words, 'large bird of prey', carry with them at least a small thrill of excitement that can't be matched by terms like 'small brown frog' or 'burrowing lizard', many of which are much less common than Powerful Owls and yet are not even regarded as rare.  But predators are the stars of the animal world and consequently more people care about them and worry about their safety than any other groups.  Powerful Owls are found from Victoria to Queensland and there may be in excess of 6000 individual animals in the wild, of which about 4000 constitute breeding pairs.  The current evidence is that the numbers have declined since European settlement, perhaps by as much as 30%, but that decline appears to have slowed, and there are many well-known populations across the species range that are within parks and conservation reserves.  For these reasons, and others, the IUCN classification is at the lowest end of threatened and the EPBC has not listed the species at all. 

Despite the apparently comfortable status of the Powerful Owl across Australia, the Victorian, NSW and Queensland governments have all classified the species as vulnerable at the state level, and have management plans in place for its long-term survival.  Compare this to the case of Victoria's Helmeted Honeyeater, where the population decline of this species was watched for nearly 100 years, and the numbers dropped to less that 50 individuals, before active steps were taken.  And this is for a popular bird which is one of the state's faunal emblems.  Reptiles and amphibians which are classified as vulnerable in Victoria (there are 12 species) mostly have known populations that number in their tens rather than thousands with the single exception of the largest reptile in the state, and its largest native predator, the Lace Goanna.

When it comes to predators our conservation strategies appear to much more careful than when dealing with smaller, less harmful animals, although this general rule does break down in the case of large, venomous snakes.