Banding and radio-tracking juvenile powerful owls in Melbourne, Victoria : trials and tribulations

The Powerful Owl (Ninox strenua) is Australia's largest owl. Considering their large size they are a very cryptic species, with limited sexual dimorphism, silent fight and a highly camouflaged presence amongst secluded canopy vegetation. These features enable Powerful Owl presence to often go unnoticed and even for the trained eye, extremely difficult to study. Our research has focused on monitoring the behaviour of individual Powerful Owls in urban Melbourne, Australia.<br />The leg banding of Powerful Owls is a somewhat contentious issue in Australia and here we report on the suitability of different types of legs bands placed on the tarsus of juvenile Powerful Owls. There has been some debate over the band size that should be used and the consequent effects bands may pose for the owls as they mature. We also investigate the usefulness of bands as a technique to identify Powerful Owls once they have dispersed from the natal territory.<br />Radio-tracking juvenile Powerful Owls was also undertaken during this study, primarily to determine individual behaviour from post fledging until dispersal. This is the first study in Australia to attempt radio-tracking juvenile Powerful Owls and the results from this research highlight behavioural characteristics, mortality rates post fledging and dispersal movements for the twelve months post fledging.<br />Overall we found that aluminium legs bands are a useful tool for individual identification of juvenile Powerful Owls post fledgling, however, their presence is somewhat difficult to determine on mature adults as the tarsus feathers tend to cover the band and make vision from the ground difficult. Aluminium leg bands are also useful as an identification tool for deceased birds. Leather leg bands are more suitable than aluminium bands when attaching radio-transmitters as these provide more flexibility and can be removed by the owl if they become irritating.<br />Radio-tracking juvenile Powerful Owls provided invaluable information relating to juvenile behaviour and movements, showing that juveniles actually remain in territories adjacent to their natal territory for the twelve months post fledging. This information is vital for the successful conservation of this species, particularly in relation to habitat conservation and home-range modelling.<br />