Sooty Owls and their prey
by Rohan Bilney

The Sooty Owl ( Tyto tenebricosa ) is a versatile hunter, consuming any small mammal up to 1kg in size, catching prey in trees and on the ground. With such a broad diet, a dietary analysis can be used as an effective technique for surveying mammals. Sooty owls, like all owls cannot digest bones and fur of their prey, and these are regurgitated back through their mouth. This regurgitated undigested material forms tight pellets (about 60mm x 30mm in length) and is found beneath owl roosts. These pellets can be collected and analysed, and the bones inside can be identified to determine the mammal species that the owls have consumed. These owls can also roost in caves, and the regurgitated pellets can accumulate, forming piles of bones, as the fur eventually breaks down. This process can occur for tens of thousands of years, so a detailed picture can emerge of the historic diet of these owls, as well as telling us what species of mammal previously occurred in a certain area.	Eastern Quoll
Conilurus	I have been studying the diet of the Sooty Owl in the Gippsland Lakes catchment for the past 18 months, and have come across a few of these old bone deposits that date back many thousands of years. As this is an ongoing study, I am yet to fully excavate these sites, to determine the total mammal species present in these deposits. An analysis of the modern fauna (possibly less than 150 years) from the top of these deposits has shown that the owls used to consume 22 native species of mammal, and many of these species no longer occur in the area, or are completely extinct. Some of these species include the White-footed Rabbit Rat, Eastern Quoll , Leadbeater's Possum and even the Hastings River Mouse, which are all species that have disappeared from the area since European Settlement. An analysis of almost 500 freshly regurgitated pellets shows that the owls now only consume 5 common species of mammal, with a preference for Sugar gliders and Greater Gliders, with barely any ground mammals being consumed (2 species now, compared with 13 historically). Some of these species of ground dwelling mammal may still occur in the area, but they are just not in the numbers they once were, and therefore not as easily accessible to owls. So there has been a massive decline in the abundance of individuals of certain ground dwelling mammal species since European Settlement in this area, be it from clearing, competition and predation from exotic species, as well as disease, or a combination of all these factors.

If any one knows the location of any Sooty Owls, or Barking Owls in Gippsland, could you please contact me.

Thanks,

Rohan Bilney

5156 9314
rjbil@deakin.edu.au