Ringtail Possums will use nest boxes wint entrance diameters up to about 90mm. However they are safer sleeping in nest boxes with smaller entrances – that Brushtail Possums (a competitor and predator species) can’t enter. This nest box design is for the minimum entrance that a Ringtail Possum will use, however you may choose to make this nest box with an entrance of 70, 75, 80, 85 or 90mm. Just beware, a small Brushtail Possum can access a nest box with an entrance of 90mm.
I have heard queries about Ringtail Possums regarding potential difficulty accessing nest boxes with these smaller entrances, when carrying young. However at my place near Canberra, both of the nest boxes that are occupied by Ringtail Possums year-round, are occupied by female Ringtails, who for part of the year are carrying young. They could choose to sleep in nest boxes with larger entrances, but have decided that (can just squeeze into) the 70mm entranced nest boxes are the safest ones to use. I have footage of them carrying the young on their bellies when entering the nest boxes – their bottoms (hips) are the biggest challenge to squeeze into the nest box entrace.
Here is a diagram with key design features for all nest boxes.
Here is some information on the different materials to use, or not to use when making your nest box.
