Monitoring of nest boxes

Nest boxes are generally deemed a useful tool in the reintroduction, conservation and monitoring of many hollow-dependent species, particularly birds. The usefulness of nest boxes for the reintroduction of western ringtail possums is however questionable. The only study so far indicated that translocated possums rarely ever used nest boxes in bush environments and that they provided no real benefits. (Moore et al, 2010)

The study was however only conducted over one season and with a small sample size. Nest box use might be a seasonal feature and/or their usefulness limited to areas with lack of other denning opportunities and/or drey building options.  

Any investigation into this topic would necessitate strategic monitoring of the boxes which is a problematic feature in itself as checking involves some invasive actions that might drive the animals away and distort the results. 

Physical checking is labour intensive and therefore expensive particularly as the boxes have to be placed high up in the tree. Low placement could significantly reduce the uptake rate.
To gain a clear picture of uptake frequency the boxes would need to be checked daily but this constant disturbance would most likely lead to the animals’ avoidance of the box.

Glass or transparent plastic bottoms have been trialled but the box would have to be kept clear of any padding material (leaves!) and not be attractive to possums. If a box was accepted the animals tend to bring leaves and twigs into their resting quarters and obstruct the view. Identification to species level would be impossible.
The bottom would also be slippery for clawed feet and drainage hole would be difficult to apply.

In order to avoid opening a hinged lid – another major disturbance - mirrors can be inserted through the entrance hole. This would still necessitate climbing a ladder which usually causes branch movements and noise and therefore disturbance to the animal. Even if the animal does not stir, it is hard to identify a species by inserting a small mirror into a darkish space and pointing it at a curled up fur-ball at the bottom of the box.

Cameras, placed opposite the box, cause no disturbance and the species is usually easy to identify from a photo. However, in order to attract animals to use it, the box would have to be nestled in a leafy, well protected place and the movement of the surrounding foliage will trigger the camera too. Camera-monitoring boxes usually produces thousands of photos per week – sometimes without a single sighting of a ringtail. Going through the footage can be very time-consuming.

Another fairly non-invasive way is to place double sided sticky tape around the entrance hole. The collected hair samples can be identified under the microscope by a well-trained person. Laypeople would hardly be equipped and able to identify the species with any certainty though.
This method would also not reveal whether the box was truly used or whether an animal only checked it out. The tape also deteriorates fast, particularly in wet conditions.

Research on captive ringtails has shown that temperature data loggers in nest boxes are useful remote-monitoring tools. Cheap (approximately A$30 each) iButtons® or Thermochrons® can be taped to the inside floor of a box and will then record temperature in the box at set intervals for long periods of time. The difference between the ambient temperature and the box with a warm animal inside showed not only that the box was occupied but also for how long without causing disturbance to the animal. (Moore et al, 2010)

This way of monitoring is relatively easy to conduct but will most likely still be limited to serious research projects. The nest box design and the size of the box that might allow an animal to stay away from the logger, its thermal properties and whether the box might heat up in summer without an animal inside and distort the results, would all have to be factored into the analysis which would probably go beyond the capacity of a community project. 
Temperature data loggers would however allow insights into more than whether a nest box was accepted by the target species. We could investigate possible seasonality of boxes and which environmental conditions would increase or decrease box occupancy.