in preference to nesting boxes, wouldn’t it be better that, if hollow bearing trees are being cleared, the hollows themselves be collected and relocated in adjacent woodlands.

If someone could please detail how to hang a section of trunk with a hollow big enough for an owl, etc, in a living tree, that would be much appreciated. I have cotemplated it a few times, but seeing how such a section can weigh >50kg, I can't see how its physically possible from an OH&S point of view, engineering practicality, or in terms of the impact on the structural integrity of the host tree.

I vaguely recall seeing pictures of nest boxes I think intended for Glossy Black Cockatoos mounted on poles - possibly within a powerline - in either a brochure for an electricity company, or as part of an EIS - in Qld.

Erin said:

"I've recently been involved in a project where we have re-designed the development so that the removal of large hollow-bearing trees, which could potentially be used by large forest owls, is unnecessary."

But did the owl habitat or human activity around these trees change significantly as a result of the proposed development? If so, the habitat may be sufficiently degraded or human disturbances sufficiently increased to deter the owls from using the large hollow-bearing trees for nesting.

Nick, I see your point, but I doubt very much that many tree hollow-dependent bird species in Australia, especially owl species would use artificial nest sites (either boxes or hollow tree limbs/logs) mounted on a pole. Location and orientation of hollows in trees, as well as sizes of the entrance and the inside of the hollow, are extremely important.  For starters, artificial nest sites mounted on poles are likely to be more visible to predators and subject more to weather elements.

Liz, you're right that the nest box design may be inadequate for Powerful Owls. However, there are some owl species in Europe & North America that readily use nest boxes, particularly those that have been placed in conifer forests. Equally so, there are other owl species in those continents that don't use nest boxes of any material, shape, size, location or orientation. It could be that most owl species in Australia also belong to that latter category, or that we have not yet found that magic formula.

I think there are some questions confounded here - it may not be that Powerful Owls are precious about using nest boxes or that the habitat is no longer suitable, but that the design of the boxes is inadequate.

Yes that is one main point. Even if hollow logs are used as potential nest sites, the area in which they would be located would be degraded (land cleared or modified) and possibly subject to disturbances (e.g. excessive noise, lighting, impacts from other human activities, etc.). 

Secondly, there have been no studies that show that Powerful Owls (or other Australian owls) readily take up residence in artificially-placed tree hollows. As Rod Kavanagh says, there is a need for these types of studies, but I would add that they have to be done in a carefully controlled scientific (experimental) manner rather than in ad hoc or opportunistic ways. Without these studies it is unacceptable to assume that provision of nest boxes or hollow logs for owls would be effective mitigation measures for developments.

Stephen et al. I’m guessing there is no published literature on this but, in preference to nesting boxes, wouldn’t it be better that, if hollow bearing trees are being cleared, the hollows themselves be collected and relocated in adjacent woodlands. This does cross over with the issue of securing them to trees ("How to erect nesting boxes" - forum discussion) and ensuring that this does not reduce the health of those plants. I’m guessing that, with reference to Stephen Debus' comment’s, even if this was done and the site cleared the extent of foraging resources would be reduced, thereby causing any owls (and other hollow utilising species) to disperse from the area.

Some additional comments from Stephen Debus, University of New England, Armidale:

"There's really nothing I can add to Rod's comments, with which I agree; he's being suitably cautious. I've said as much in my owl book (just out). You can pass my comment on to the forum if you like, but I think there's nothing else to say until someone does some proper, scientifically based tests of nest-box use and breeding productivity in owl habitats lacking natural hollows. And developments probably remove foraging habitat as well as nest sites, so one would need to control for foraging habitat and food supply while testing nest-box use. Owls may well acceptboxes if there's plenty of food, but not if there's little food."

The publication that Stephen refers to in his email is:

Debus, S.J.S. (2009). The Owls of Australia: A Field Guide to Australian Night Birds (Envirobook, Canterbury, NSW).